সোমবার, ২৩ জুন, ২০২৫
শনিবার, ২১ জুন, ২০২৫
1 Hour Timer
A simple battery operated one hour timer device with an audible warning. May be used as a parking meter timer.
Circuit Notes:
This circuit uses just two CMOS IC's, a 4011 quad 2 input NAND gate, and a 4020 14-stage ripple binary counter. At switch on R2 and C2 provide a brief reset pulse, which will ensure the output pin Q1 of the 4020 is high. Gates U1 and U2 form a simple astable R1 and C1 determining the timing period. The tolerances of capacitors vary widely, so for more control, you may use a 470n capacitor for C1 and use a fixed 3.3M resistor in series with a 250k preset for R1. A timing period of just less than 1.76seconds is required.
The output of the oscillator at U2 drives the input of the 14-stage ripple counter, U3.
The outputs divide sequentially by two and the output signal is taken from Q13, requiring 2048 input pulses before the signal becomes high.
When the ouput Q13 goes high, the output sounder will become active. Gate U4 of the 4011 is used to "modulate" the output sounder. As U4 is also connected to the output of U2, the output sounder will turn on and off at the same rate as the oscillator.
Suitable output sounders can be found at Maplin Electronicspart code KU56L or CR34M. These are self contained DC piezo buzzers, requiring 10mA at 12V DC but work with supply voltages from 3 to 15 Volts DC.
The graph below is from the simulation version of this circuit. In the simulated version I have tapped the output of the CMOS4020 at Q5, therefore only 8 input pulses from the oscillator (shown in green trace) are required before the Q5 output switches to high (shown as blue trace).
The top waveform in red, is the output across the output sounder. As can be seen, this output is switched on and off as long as the output pin, Q5 is active. To simulate the sounder, I have used a fixed resistor.
Calibration:
Here comes the maths. One hour or 3600 seconds divided by 2048 pulses (Q13) requires a timed period of 1.7578 seconds. The timing for a CMOS oscillator, varies with supply voltage, but is approximately 1.1 RC. To acheive the timed period, C1 is 0.47u and R1 is made from a fixed 3.3M resistor in series with a 250k
preset.
To adjust this value, connect a low current LED and dixed 2.2k resitor to the output of IC2. The LED should illuminate on each pulse. Adjust the 250k preset until the LED flashes about 34 times per minute (60/34 = 1.76s). If you would like to use this a parking meter timer, then set the unit to trigger before the hour is up or start the timer before you feed the meter to allow extra time.
Simple variable frequency oscillator
This is a very simple circuit utilising a 555 timer IC to generate square wave of frequency that can be
adjusted by a potentiometer.
With values given the frequency can be adjusted from a few Hz to several Khz.
To get very low frequencies replace the 0.01uF capacitor with a higher value.
The formula to calculate the frequency is given by:
1/f = 0.69 * C * ( R1 + 2*R2)
The duty cycle is given by:
% duty cycle = 100*(R1+R2)/(R1+ 2*R2)
In order to ensure a 50% (approx.) duty ratio, R1 should be very small when compared to R2. But R1
should be no smaller than 1K. A good choice would be, R1 in kilohms and R2 in megaohms. You can then
select C to fix the range of frequencies.
এটি একটি খুব সহজ সার্কিট যা 555 টাইমার আইসি ব্যবহার করে ফ্রিকোয়েন্সির বর্গাকার তরঙ্গ তৈরি করে যা
একটি পোটেনশিওমিটার দ্বারা সামঞ্জস্য করা যেতে পারে।প্রদত্ত মান অনুসারে ফ্রিকোয়েন্সি কয়েক Hz থেকে কয়েক Khz এ সামঞ্জস্য করা যেতে পারে।
খুব কম ফ্রিকোয়েন্সি পেতে 0.01uF ক্যাপাসিটরকে একটি উচ্চ মানের সাথে প্রতিস্থাপন করুন।
ফ্রিকোয়েন্সি গণনা করার সূত্রটি নিম্নরূপ:
1/f = 0.69 * C * ( R1 + 2*R2)
শুল্ক চক্র নিম্নরূপ:
% শুল্ক চক্র = 100*(R1+R2)/(R1+ 2*R2)
50% (প্রায়) শুল্ক অনুপাত নিশ্চিত করার জন্য, R2 এর তুলনায় R1 খুব ছোট হওয়া উচিত। কিন্তু R1
1K এর চেয়ে কম হওয়া উচিত নয়। একটি ভাল পছন্দ হবে, R1 কিলোহমে এবং R2 মেগাওহমে। তারপর আপনি
ফ্রিকোয়েন্সির পরিসর ঠিক করতে C নির্বাচন করতে পারেন।
Time Delay Relay
When activated by pressing a button, this time delay relay will activate a load after a specified amount of
time. This time is adjustable to whatever you want simply by changing the value of a resistor and/or
capacitor. The current capacity of the circuit is only limited by what kind of relay you decide to use.
Parts:
C1 See Notes
R1 See Notes
D1 1N914 Diode
U1 4011 CMOS NAND Gate IC
K1 6V Relay
S1 Normally Open Push Button Switch
MISC Board, Wire, Socket For U1
Notes:
1. To calculate the time delay, use the equation R1 * C1 * 0.85=T, where R1 is the value of R1 in Ohms,
C1 is the value of C1 in uF, and T is the time delay in seconds.
2. S1 may be replaced with an NPN transistor so the circuit can be triggered by a computer, other circuits,
etc.
3. Most any 6V relay will work for K1. If you use a large relay, you my need to add a transistor to the
output of the circuit in order to drive the larger load.
সময়। এই সময়টি আপনি যা চান তা কেবল একটি রেজিস্টার এবং/অথবাক্যাপাসিটরের মান পরিবর্তন করে সামঞ্জস্য করতে পারেন। সার্কিটের বর্তমান ক্ষমতা কেবলমাত্র আপনি কোন ধরণের রিলে ব্যবহার করবেন তার উপর সীমাবদ্ধ।
দ্রষ্টব্য:
১. সময় বিলম্ব গণনা করতে, R1 * C1 * 0.85=T সমীকরণটি ব্যবহার করুন, যেখানে R1 হল Ohms-এ R1-এর মান,
C1 হল uF-এ C1-এর মান, এবং T হল সেকেন্ডে সময় বিলম্ব।
২. S1-কে একটি NPN ট্রানজিস্টর দিয়ে প্রতিস্থাপন করা যেতে পারে যাতে সার্কিটটি একটি কম্পিউটার, অন্যান্য সার্কিট,
ইত্যাদি দ্বারা ট্রিগার করা যায়।
৩. বেশিরভাগ 6V রিলে K1-এর জন্য কাজ করবে। আপনি যদি একটি বড় রিলে ব্যবহার করেন, তাহলে বৃহত্তর লোড চালানোর জন্য আপনাকে সার্কিটের
আউটপুটে একটি ট্রানজিস্টর যুক্ত করতে হবে।
Periodic Timer
Notes:
This timer circuit is similar to the 5 to 30 minute timer except that when switch S1 is closed, the on/off
action of the circuit will continue indefinately until S1 is opened again. A 7555 time and low leakage type
capacitor for C1 must be used. The 6 way rotary switch S3 adds extra resistance in series to the timing
chain with each rotation, minimum resistance point "a" maximum point "f". The 7555 is wired as an equal
mark/space ratio oscillator, the timing resistor chain R1 to R6, being connected back to the output of the
timer at pin 3.The output pulse duration is defined as:-
T = 1.4 R1 C1
This gives on and off times of about 379 seconds for postion "a" of S3 (just over 6 minutes), to about 38
minutes at point "f". The times may of coourse be varied by altering R1 to R6 or C1.
1KHz Sinewave Generator
Simple circuitry, low distortion, battery operated
Variable, low impedance output up to 1V RMS
Circuit diagram
Parts:
R1 5K6 1/4W Resistor
R2 1K8 1/4W Resistor
R3,R4 15K 1/4W Resistors
R5 500R 1/2W Trimmer Cermet
R6 330R 1/4W Resistor
R7 470R Linear Potentiometer
C1,C2 10nF 63V Polyester Capacitors
C3 100µF 25V Electrolytic Capacitor
C4 470nF 63V Polyester Capacitor
Q1,Q2 BC238 25V 100mA NPN Transistors
LP1 12V 40mA Lamp (See Notes)
J1 Phono chassis Socket
SW1 SPST Slider Switch
B1 9V PP3
Clip for 9V PP3 Battery
This circuit generates a good 1KHz sinewave using the inverted Wien bridge configuration (C1-R3 & C2
R4). Features a variable output, low distortion and low output impedance in order to obtain good overload
capability. A small filament lamp ensures a stable long term output amplitude waveform. Useful to test the
Audio Millivoltmeter, Audio Power Meter and other audio circuits published in this site.
Notes:
The lamp must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term
stability and low distortion.
Distortion @ 1V RMS output is 0.15% with a 12V 40mA lamp, raising to 0.5% with a 12V 100mA one.
Using a lamp differing from specifications may require a change in R6 value to 220 or 150 Ohms to ensure
proper circuit's oscillation.
Set R5 to read 1V RMS on an Audio Millivoltmeter connected to the output with R7 fully clockwise, or to
view a sinewave of 2.828V Peak-to-Peak on the oscilloscope.
With C1,C2 = 100nF the frequency generated is 100Hz and with C1,C2 = 1nF frequency is 10KHz but R5 is
needing adjustment.
High gain transistors preferred for better performance.
সহজ সার্কিট, কম বিকৃতি, ব্যাটারি চালিত পরিবর্তনশীল, 1V RMS পর্যন্ত কম প্রতিবন্ধকতা আউটপুট সার্কিট ডায়াগ্রাম অংশ: R1 5K6 1/4W রেজিস্টর R2 1K8 1/4W রেজিস্টর R3,R4 15K 1/4W রেজিস্টর R5 500R 1/2W ট্রিমার সার্মেট R6 330R 1/4W রেজিস্টর R7 470R লিনিয়ার পটেনশিওমিটার C1,C2 10nF 63V পলিয়েস্টার ক্যাপাসিটর C3 100µF 25V ইলেক্ট্রোলাইটিক ক্যাপাসিটর C4 470nF 63V পলিয়েস্টার ক্যাপাসিটর Q1,Q2 BC238 25V 100mA NPN ট্রানজিস্টর LP1 12V 40mA ল্যাম্প (নোট দেখুন) J1 ফোনো চ্যাসিস সকেট SW1 SPST স্লাইডার সুইচ B1 9V PP3 ক্লিপ 9V PP3 ব্যাটারির জন্য এই সার্কিটটি ভালো একটি উত্পন্ন করে ইনভার্টেড উইয়েন ব্রিজ কনফিগারেশন (C1-R3 এবং C2 R4) ব্যবহার করে 1KHz সাইনওয়েভ। ভালো ওভারলোড ক্ষমতা অর্জনের জন্য একটি পরিবর্তনশীল আউটপুট, কম বিকৃতি এবং কম আউটপুট প্রতিবন্ধকতা রয়েছে।
একটি ছোট ফিলামেন্ট ল্যাম্প একটি স্থিতিশীল দীর্ঘমেয়াদী আউটপুট প্রশস্ততা তরঙ্গরূপ নিশ্চিত করে। এই সাইটে প্রকাশিত অডিও মিলিভোল্টমিটার, অডিও পাওয়ার মিটার এবং অন্যান্য অডিও সার্কিট পরীক্ষা করার জন্য দরকারী।
দ্রষ্টব্য:
ভালো দীর্ঘমেয়াদী স্থিতিশীলতা এবং কম বিকৃতি পেতে ল্যাম্পটি অবশ্যই একটি কম কারেন্ট টাইপ (12V 40-50mA বা 6V 50mA) হতে হবে। 12V 40mA ল্যাম্পের সাথে 1V RMS আউটপুট @ বিকৃতি 0.15%, 12V 100mA ল্যাম্পের সাথে 0.5% পর্যন্ত বৃদ্ধি পায়। স্পেসিফিকেশন থেকে ভিন্ন ল্যাম্প ব্যবহার করার জন্য সঠিক সার্কিটের দোলন নিশ্চিত করতে R6 মান 220 বা 150 Ohms এ পরিবর্তন করতে হতে পারে। R7 সম্পূর্ণ ঘড়ির কাঁটার দিকে আউটপুটের সাথে সংযুক্ত একটি অডিও মিলিভোল্টমিটারে 1V RMS পড়ার জন্য R5 সেট করুন, অথবা অসিলোস্কোপে 2.828V পিক-টু-পিক সাইনওয়েভ দেখুন। C1,C2 = 100nF এর সাথে উৎপন্ন ফ্রিকোয়েন্সি 100Hz এবং C1,C2 = 1nF এর সাথে 10KHz কিন্তু R5 এর সমন্বয় প্রয়োজন। উন্নত কর্মক্ষমতার জন্য উচ্চ লাভ ট্রানজিস্টর পছন্দনীয়।
NE555 Basic Monostable
otes:
Here the popular 555 timing IC, is wired as a monostable. The timing period is precise and equivalent to:-
1.1 x R1 x C1
With component values shown this works out at approximately 1.1msec.The output duration is independant
of the input trigger pulse, and the output from the 555 is buffered and can directly interface to CMOS or
TTL IC's, providing that the supply voltages match that of the logic family.
The timing diagram above shows the output pulse duration, the trigger input and the output at the
discharge terminal of the IC.
Downed Model Locator
If you know people who fly slope gliders frequently, you probably know someone who has lost a glider in
the weeds or bushes. Here is a circuit I've shamelessly swiped from George Steiner's book "A to Z - Radio
Control Electronic Journal" that may help you find your glider. I modified the circuit to use parts currently
available at your local Radio Shack store, and modified it to decrease false triggering from low voltage
spikes in the on-board power system when full sized or higher torque servos are used.
Your transmitter sends a set of pulses to your receiver every 20 milliseconds, and your receiver in turn
sends an individual pulse to each of your servos at the same interval. This circuit is a pulse omission
detector--an alarm sounds when the pulses, originating from your transmitter, are no longer present. By
plugging this circuit into an unused servo socket on your receiver, you can turn on the alarm by turning off
your transmitter.
The first capacitor C1 filters out DC voltage, preventing an aggressive automatic gain control of some
current receivers from shutting off the alarm even when your transmitter is off. The first transistor Q1
serves to flip the pulse to negative modulation that the 555 needs. The C2 capacitor and the R4 resistor
establish the time interval--if no pulse is received in the time it takes to charge the capacitor through the
resistor, the alarm sounds. The interval is the resistance multiplied by the capacitance: 1uF x 47k =
0.000001F x 47000 ohms = 0.047sec = 47msec which is a little over twice the standard 20msec R/C frame
rate--this device uses a little longer interval than the frame rate to prevent false triggering. The other
capacitor C3 smoothes the control voltage on the 555, preventing false triggering from spikes in the supply
voltage. Unless a pulse opens the Q2 transistor to drain the C2 capacitor before the capacitor is fully
charged, the pin 6 threshold senses a high voltage and triggers the output pin 3 to go low, sinking current
across the buzzer and making noise. With the reset pin 4 high, the discharge pin 7 drains the capacitor,
and the cycle starts again.
The circuit draws 1mA (!) when idle and 4 mA when buzzing. I've been using large peizo buzzers (see part
numbers below) because they are light and loud, and the 6 volt electromagnetic buzzer where weight is not
so much of a concern.
The circuit uses your receiver battery for power. For the ultimate in reliability, you can use an additional
battery to supply the alarm as follows. Connect only signal and negative leads to your receiver socket, and
connect the second battery positive to positive circuit lead and negative to negative circuit lead. You will
need to put some kind of switch in series with the second battery to keep it from running the alarm when
you are not flying. With the extra battery, you will still be able to find your plane if your plane went down
380
because of a receiver battery failure, or if your receiver battery fell out in the crash. You can use a nine
volt battery for this, but be careful to NOT connect the nine volt battery to your receiver--or you will smoke
your receiver. Note: Do NOT solder to a button battery--they explode.
Here are few Radio Shack parts numbers. You can substitute other types of capacitors; tantalum capacitors
are just physically smaller. Polarity of the tantalum capacitor probably does not matter at this low voltage
(compared to the rated maximum voltage), but to be particular, the positive lead would be directed toward
the input signal lead and away from the negative side. Power in this circuit is minimal and you can use the
smallest resistors you can get your hands on (get 1/8 watt if you can, but any power rating will work).
273-065 peizo buzzer
273-054 electric buzzer
276-1604 2N3906-type PNP transistors, 15 per
276-2016 2N3904 NPN transistor
276-1723 LM555 timer IC
272-1434 1uF tantalum capacitor
271-xxx 1/4 watt resistors (10k, 47k, 4.7k, 5 per)
George Steiner's book, crammed with cool R/C radio info, can be had for $19.95 postage paid from the
Adjustable High/Low Frequency Sine wave generator
This circuit uses the versatile MAX038 function generator. Although in this circuit some of the advanced
characteristics of this IC are disabled, you can generate Sine, Triangle, Square waves (adjusting A0 and A1
pins see datasheet on www.maxim-ic.com if you want other waves, use a switch).
The signal is amplified through a TCA0372 (from ONSEMI) Power opamp with current capability up to 1A
and bandwitch up to 1 MHz.
I selected this particular frequency (122 Khz) because i needed a cheapo ESR-o-meter for my electrolytic
capacitors to monitor their health as they have to discharge tens of amperes in less than 2 ms. At 122 KHz
capacitive reactance is very low, and inductive reactance isn't so high, so forcing a current (es 200mA,
using a precision resistor) through a capacitor and reading AC voltage drop accross it gives me an
estimation of ESR (Vdrop/current). Of course inductive and capacitive reactance are still present, but
negligible.Let's back to the circuit.
peration:
The 122 khz 2V p-p sine wave is generated by the MAX038 IC, its frequency can be calculated by the
formula Freq (MHz) = Iin(uA) / C6 (pf) Iin = 2,5V / R1 (25Kohm default). So the freq is 0,122 MHz . The
resistor is for small adjustments, don't go under 10000 Kohm or above 40000 Kohm because the accuracy
will drop. If you want multifrequency just use the multiposition switch with 820 pF, 8,2 nF , 82nF , 820 nf
for 122Khz range 12,2Khz range 1220 Hz and 122 Hz. Fine tuning can be done adjusting R2 , the
frequency can vary from 1,7x (Vfadj = -2,4) to 0,3x (Vfadj = 2,4) of the main frequency (when fadj is at
0V).
The sine wave output is feed into a TCA0372 1/2 opamp to achieve a gain from 1 to 5 (2V p-p, 10 V p-p),
adjust the potenziometer and into a TCA0372 2/2 opamp buffer stage also present on the same IC.
Important:
Adjusting the frequency needs a frequency counter, so this circuit should be used on conjunction with a
freq couter. The max current is 1A, but i would suggesto to not go above 0,5A to remain accurate. Needs a
computer power supply with 12V,5V,-5V,-12V,GND to be operated, if you don't have one just use a
multivoltage mains transformer (15 watt is enough) diode bridges (low current 1-2 Amps), smoothing
capacitors 10000uF 16V, and voltage regulators such as LM7905 and LM7912.
CAR Headlights Timer
ushbutton activated
Very simple circuitry
R1 4K7 1/4W Resistor
R2,R3 1K 1/4W Resistors
C1 100µF 25V Electrolytic Capacitor (See Notes)
D1 1N4002 100V 1A Diode
Q1 BC547 45V 100mA NPN Transistor
Q2 BC327 45V 800mA PNP Transistor
P1 SPST Pushbutton
RL1 Relay with SPDT 10A min. switch
Coil Voltage 12V. Coil resistance 150-600 Ohms
Comments:
This device is a simple timer, allowing to keep on the headlights of your vehicle for about 1min. and
30sec., e.g. when accessing some dark place, without the necessity of coming back to switch-off the lights.
Circuit operation:
Pushing on P1 allows C1 charging to full 12V battery supply. Therefore Q1 is driven hard-on, driving in turn
Q2 and its Relay load. The headlights are thus activated by means of the Relay contact wired in parallel to
the vehicle's headlights switch. RL1 remains activated until C1 is almost fully discharged, i.e. when its
voltage falls below about 0.7V.
The timing delay of the circuit depends by C1 and R1 values and was set to about 1min. and 30sec.
In practice, due to electrolytic capacitors wide tolerance value, this delay will vary from about 1min. and
30sec. to 1min. and 50sec.
An interesting variation is to use the inside lamp as a command source for the timer. In this way, when the
door is opened C1 is charged, but it will start to discharge only when the door will be closed, substituting
pushbutton operation.
To enable the circuit acting in this way, simply connect the cathode of a 1N4002 diode to R1-C1 junction
and the anode to the "live" lead of the inside lamp.
This lead can be singled-out using a voltmeter, as it is the lead where a 12V voltage can be measured in
respect to the vehicle frame when the lamp is on.
Notes:
The Relay contact must be rated at 10A or more.
Timings obtained trying different tolerance electrolytic capacitors for C1:
100µF = 1'30" to 1'50"
47µF = 0'45" to 1'05"
220µF = 3'15" to 4'15"
Pulse-Generator & Signal-Tracer
Dual-purpose test-instrument
Very simple circuitry, 1.5V Battery-operated
Parts:
R1 1M 1/4W Resistor
R2,R4 2K7 1/4W Resistors
R3 150K 1/4W Resistor
C1 2n2 630V Ceramic or Polyester Capacitor (See Notes)
C2,C3 4n7 63V Ceramic or Polyester Capacitors
D1 1N4148 75V 150mA Diode
Q1 BC547 45V 100mA NPN Transistor
Q2 BC557 45V 100mA PNP Transistor
SW1 SPST miniature Slider Switch (See Notes)
J1 Stereo switched 3mm. Jack socket (See Notes)
Probe Metal Probe 3 to 5 cm. long
Clip Miniature Crocodile Clip
B1 1.5V Battery (AA or AAA cell etc.)
Device purpose:
This simple circuit generates narrow pulses at about 700-800Hz frequency. The pulses, containing
harmonics up to the MHz region, can be injected into audio or radio-frequency stages of amplifiers,
receivers and the like for testing purposes. A high-pitched tone can be heard from the speaker of the
device under test when all is working properly. The clip must be connected to the ground of the device
under test, touching with the probe the different stages of the circuit, starting from the last stage and
going up towards the first. When the tone is no longer heard, the defective stage has been found.
Connecting an earclip or headphone to J1, the circuit will automatically change into a two-stage amplifier
and any audio signal coming from the device under test and picked-up by the probe will be heard through
the headphones. The testing of a circuit should be made in the reverse manner, i.e. starting from the first
stage and going down until the last stage. When nothing is heard, the defective stage has been found.
Circuit operation:
Q1 & Q2 form a complementary astable multivibrator, whose operating frequency is set mainly by R3, C2 &
C3 values. Output pulses are taken at Q2 Collector and applied to the probe by means of decoupling
capacitor C1. D1 provides a symmetrical shape for the output waveform.
If an earclip or headphone jack is plugged into J1, the connection from Q2 Collector and C1-C2 is broken
by the switch incorporated into J1: in this case the circuit becomes a two-stage amplifier.
Notes:
If you intend to use the circuit to test valve operated devices C1 must be a 630V type. Working with low
voltage supply transistor devices the voltage of C1 can be lowered to 63 or 100V.
If instead of a short probe, you intend to connect the circuit to the device under test by means of a piece of
wire longer than a few centimeters, a small ceramic capacitor (470 to 1000pF) should be added in parallel
to D1 to prevent unwanted RF oscillation.
Current drawing when in Pulse-Generator mode is about 60µA and 1.2mA when in Signal-Tracer mode
operation. Therefore SW1 can be omitted, provided that the earclip or headphones are unplugged when the
circuit is unused.
J1 is a stereo switched jack socket wired to obtain a series connection of the two earpieces forming a
stereo headphone. In this manner the circuit is loaded with a higher impedance and sensitivity will be
improved.
Therefore, the higher the load impedance the more sensitive the Signal-Tracer. In any case, common 32
Ohm impedance mini-headphones suitable for walkman sets will work fine.
A crystal (high impedance) earpiece is a good solution, provided you substitute J1 with a mono switched
jack socket.
The entire circuit can be easily fitted into a pen-like enclosure, with the probe protruding like a nib.
Ultrasonic Dog Whistle
venerable 555, of course) with a variable pitch and a relatively loud 82 dB miniature piezo beeper. The
circuit is very simple and can be easily assembled in half an hour. Most of the components are not really
critical, but you should keep in mind that other values will probably change the operating frequency.
Potentiometer determines the pitch: higher resistance means lower frequency. Since different dogs react to
different frequencies, you'll probably have to experiment a bit to get the most out of this tiny circuit. The
circuit is shown below:
Circuit diagram
Despite the simplicity of the circuit, there is one little thing. The 10nF (.01) capacitor is critical as it, too,
determines the frequency. Most ceramic caps are highly unstable and 20% tolerance is not unusual at all.
Higher capacitance means lower frequency and vice-versa. For proper alignment and adjustment, an
oscilloscope would be necessary. Since I don't have one, I used Winscope. Although it's limited to only 22
kHz, that's just enough to see how this circuit works. There is no need to etch a PCB for this project, perf
board will do. Test the circuit to see how it responds at different frequencies. A 4k7 potentiometer in
conjunction with a 10nF (or slightly bigger) capacitor gives some 11 to 22kHz, which should do just fine.
Install the circuit in a small plastic box and if you want to, you can add a LED pilot light. Power
consumption is very small and a 9V battery should last a long time. Possible further experimentation: I'm
working on an amplified version of the whistle to get a louder beep. All attempts so far haven't been
successful as high frequency performance tends to drop dramatically with the 555. Perhaps I could use a
frequency doubler circuit - I just don't know and I've run out of ideas. One other slightly more advanced
project could be a simple "anti-bark" device with a sound-triggered (clap) switch that sets off the ultrasonic
buzzer as soon as your dog starts to bark
এটা সকলেই জানেন যে অনেক প্রাণীই উচ্চ-ফ্রিকোয়েন্সি শব্দের প্রতি বিশেষভাবে সংবেদনশীল যা মানুষ
শুনতে পারে না। এই নীতির উপর ভিত্তি করে অনেক বাণিজ্যিক কীটপতঙ্গ নিবারক পাওয়া যায়, যার বেশিরভাগই
30 থেকে 50 kHz এর মধ্যে কাজ করে। তবে, আমার লক্ষ্য ছিল একটি সামান্য ভিন্ন এবং কিছুটা বেশি শক্তিশালী
অডিও ফ্রিকোয়েন্সি/আল্ট্রাসনিক শব্দ জেনারেটর ডিজাইন করা যা কুকুরদের প্রশিক্ষণের জন্য ব্যবহার করা যেতে পারে। সম্ভাবনাগুলি কল্পনা করুন -
আপনি রাতের মাঝখানে আবার ঘেউ ঘেউ করার আগে আপনার পোষা প্রাণীকে দুবার ভাবতে বাধ্য করতে পারেন অথবা এমনকি শত্রু
কুকুরদের দমন করতে পারেন (এবং আমার ধারণা চোররা এটি পছন্দ করবে!)। আমি যা পড়েছি তা থেকে, কুকুর এবং একই আকারের অন্যান্য স্তন্যপায়ী প্রাণী
পোকামাকড়ের চেয়ে অনেক আলাদা আচরণ করে। তারা 15 থেকে 25 kHz এর মধ্যে ফ্রিকোয়েন্সিতে সবচেয়ে ভালো সাড়া দেয়
এবং বয়স্করা উচ্চ স্বরের প্রতি কম সংবেদনশীল। এর মানে হল যে একটি সাধারণ কীটপতঙ্গ নিবারক
কাজ করবে না কারণ কুকুর এটি শুনতে পায় না। অতএব, আমি একটি নতুন সার্কিট তৈরি করার সিদ্ধান্ত নিলাম (অবশ্যই
পূজনীয় 555 এর উপর ভিত্তি করে) যার একটি পরিবর্তনশীল পিচ এবং তুলনামূলকভাবে জোরে 82 dB ক্ষুদ্র পাইজো বিপার থাকবে।
সার্কিটটি খুবই সহজ এবং আধ ঘন্টার মধ্যে সহজেই একত্রিত করা যাবে। বেশিরভাগ উপাদানই আসলে
গুরুত্বপূর্ণ নয়, তবে আপনার মনে রাখা উচিত যে অন্যান্য মান সম্ভবত অপারেটিং ফ্রিকোয়েন্সি পরিবর্তন করবে।
পটেনশিওমিটার পিচ নির্ধারণ করে: উচ্চতর প্রতিরোধের অর্থ কম ফ্রিকোয়েন্সি। যেহেতু বিভিন্ন কুকুর
বিভিন্ন ফ্রিকোয়েন্সিতে প্রতিক্রিয়া দেখায়, তাই এই ক্ষুদ্র সার্কিট থেকে সর্বাধিক সুবিধা পেতে আপনাকে সম্ভবত কিছুটা পরীক্ষা করতে হবে।
সার্কিটটি নীচে দেখানো হয়েছে:
সার্কিটের সরলতা সত্ত্বেও, একটি ছোট জিনিস রয়েছে। 10nF (.01) ক্যাপাসিটরটিও গুরুত্বপূর্ণ কারণ এটি
ফ্রিকোয়েন্সি নির্ধারণ করে। বেশিরভাগ সিরামিক ক্যাপ অত্যন্ত অস্থির এবং 20% সহনশীলতা মোটেও অস্বাভাবিক নয়।
উচ্চতর ক্যাপাসিট্যান্স মানে কম ফ্রিকোয়েন্সি এবং তদ্বিপরীত। সঠিক সারিবদ্ধকরণ এবং সমন্বয়ের জন্য, একটি
অসিলোস্কোপ প্রয়োজন হবে। যেহেতু আমার কাছে একটি নেই, আমি Winscope ব্যবহার করেছি। যদিও এটি মাত্র 22
kHz-এর মধ্যে সীমাবদ্ধ, এই সার্কিটটি কীভাবে কাজ করে তা দেখার জন্য এটি যথেষ্ট। এই প্রকল্পের জন্য PCB খোদাই করার প্রয়োজন নেই, পারফ
বোর্ডটি করবে। বিভিন্ন ফ্রিকোয়েন্সিতে এটি কীভাবে প্রতিক্রিয়া দেখায় তা দেখার জন্য সার্কিটটি পরীক্ষা করুন। 10nF (অথবা সামান্য বড়) ক্যাপাসিটরের সাথে
সংযোগে একটি 4k7 পোটেনশিওমিটার প্রায় 11 থেকে 22kHz দেয়, যা ঠিকঠাক কাজ করবে।
একটি ছোট প্লাস্টিকের বাক্সে সার্কিটটি ইনস্টল করুন এবং আপনি যদি চান, আপনি একটি LED পাইলট লাইট যোগ করতে পারেন।
বিদ্যুতের ব্যবহার খুব কম এবং একটি 9V ব্যাটারি দীর্ঘ সময় ধরে চলবে। সম্ভাব্য আরও পরীক্ষা: আমি
জোরে বীপ পেতে হুইসেলের একটি পরিবর্ধিত সংস্করণে কাজ করছি। এখন পর্যন্ত সব প্রচেষ্টা সফল হয়নি কারণ ৫৫৫ এর সাথে উচ্চ ফ্রিকোয়েন্সি কর্মক্ষমতা নাটকীয়ভাবে হ্রাস পায়। সম্ভবত আমি একটি
ফ্রিকোয়েন্সি ডাবলার সার্কিট ব্যবহার করতে পারি - আমি জানি না এবং আমার কোনও ধারণা নেই। আরেকটি সামান্য উন্নত
প্রকল্প হতে পারে একটি সাধারণ "অ্যান্টি-বার্ক" ডিভাইস যার একটি শব্দ-ট্রিগার (তালি) সুইচ রয়েছে যা আপনার কুকুর ঘেউ ঘেউ শুরু করার সাথে সাথে আল্ট্রাসনিক
বাজারটি বন্ধ করে দেয়।
A circuit diagram that can be used for the generation of CW Morse code is shown here.
This circuit can be very useful those who would like practice Ham Radio.
The circuit is nothing but an astable multivibrator based on NE 555.
The frequency of oscillations of the circuit depends on the components R1,R2 & C1.
The circuit can be powered from a 9V PP3 battery.
Notes.
• The POT R2 can be used for frequency adjustments.
• POT R3 can be used for volume adjustments.
• The switch S1 can be a Morse code key.
বর্ণনা।
CW মোর্স কোড তৈরির জন্য ব্যবহার করা যেতে পারে এমন একটি সার্কিট ডায়াগ্রাম এখানে দেখানো হয়েছে। যারা হ্যাম রেডিও অনুশীলন করতে চান তাদের জন্য এই সার্কিটটি খুবই কার্যকর হতে পারে। সার্কিটটি NE 555 এর উপর ভিত্তি করে একটি আশ্চর্যজনক মাল্টিভাইব্রেটর ছাড়া আর কিছুই নয়। সার্কিটের দোলনের ফ্রিকোয়েন্সি R1, R2 এবং C1 উপাদানগুলির উপর নির্ভর করে। সার্কিটটি 9V PP3 ব্যাটারি থেকে চালিত হতে পারে।
বিঃদ্রঃ। • ফ্রিকোয়েন্সি সমন্বয়ের জন্য POT R2 ব্যবহার করা যেতে পারে। • ভলিউম সমন্বয়ের জন্য POT R3 ব্যবহার করা যেতে পারে।
LASER Transmitter/Receiver
This set of two circuits from the basis for a very simple light wave transmitter. A LASER beam is modulated
and then aimed at a receiver that demodulates the signal and then presents the information (voice, data,
etc..). The whole thing is very easy to build and requires no specialized parts execpt for the LASER itself.
LASERs are available from MWK Industries.
Parts:
C1, C2 0.1uf Ceramic Disc Capacitor
C3 100uf 25V Electrolytic Capacitor
R1 100K Ohm 1/4W Resistor
R2 1M Ohm 1/4W Resistor
R3 10K Pot
Q1 NPN Phototransistor
U1 741 Op Amp
U2 LM386 Audio Amp
SPKR1 8 Ohm Speaker
T1 8 Ohm:2K Audio Transformer
MISC Wire, Board, Knob For R3, LASER Tube and Power Supply
1. In the transmitter schematic, no ballast resistor is shown because most small LASER power supplies
already have one built in. Yours may differ, and a resistor may be needed.
2. The receiver should be kept away from bright lights. You may want to put a piece of wax paper in front
of Q1 to keep the LASER from swamping it.
3. In order to get any decent amount of modulation, you may need to drive T1 with more then a watt.
4. The circuit can be made to transmit computer data with the use of two modem chips.
Magnetic-Radiation Remote-Control
Short-range 35KHz operation, single-channel unit
Simple circuitry, no outer antennas required
Transmitter circuit diagram:
C1 4n7 630V Ceramic or Polyester Capacitor
C2 60-80pF 63V Ceramic Trimmer
C3 100µF 25V Electrolytic Capacitor
Q1 BC337 45V 800mA NPN Transistor
Q2 BD139 80V 1.5A NPN Transistor
L1 500 turns on a 10mm. diameter, 10cm. long ferrite rod.
Enameled wire diameter: 0.2mm.
The tap is made after 200 turns, ground side
P1 SPST Pushbutton
B1 6-9V Battery (4 to 6 AA 1.5V Cells in series, see Notes)
IR Remote Control Extender Circuit
Description:
This is an improved IR remote control extender circuit. It has high noise immunity, is resistant to ambient
বৃহস্পতিবার, ১৯ জুন, ২০২৫
The Output Adjustable Flyback Converter
Description
A high voltage step-up DC power supply using adjustable flyback conversion.
Specification
Vin = 220Vac +-10% @ 50/60Hz
Vout =0~600Vdc @ 0.25A
Switching Frequency: 70~100KHz
Design Guidelines
DCM mode, output power is 200W
The input RMS current in worse condition with discontinuous current mode may be calculated as:
If the optimum operating duty cycle is set at D=0.35, then input peak current can be found as:
Therefore the voltage sensing limit voltage level from the FAN7554 data sheet is 1.5V
Supply Voltage Indicator
Description
A novel supply voltage monitor which uses a LED to show the status of a power supply.
Notes
This simple and slightly odd circuit can clearly show the level of the supply voltage (in a larger device): as
long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted (for the naked eye)
yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get
slower and slower if the voltage drops further - giving very clear and intuitive representation of the
supply's status. The blinking will stop and LED1 will finally go out at a little below 9 volts.
On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at
14 V.
The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4.
The base-emitter diode of T2 basically just stands in for a zener diode. The emitter-collector path of T1 is
inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will
be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so
low that it no longer can cause breakdown along the emitter-collector path.
Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but
many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or
546
two more. If experimenting, be careful not to punch a hole through the device under test: they oscillate at
9-12 V or not at all.
Soft Start PSU
Description
Two soft start power supplies. The output voltage slowly increases to the desired output.
544
Notes
The output voltage rises slowly and reaches 15 V in 5 seconds.
In order to perform this soft-start function, the LM317 voltage regulator IC requires an external universal
PNP transistor and the L200 uses its internal comparator (pin 2).
After switch-on, the rising voltage on the positive side of the charging electrolytic capacitor slowly turns the
(initially conducting) transistor off, thus raising the voltage (relative to ground) on the adjustment pin of
the LM317. In the L200 circuit, the corresponding electrolytic capacitor's rising voltage gradually relaxes
the current-regulation loop inside the L200.
Small Variable power Supply
Description
Features: 1.3-12.2 V, 1 A, over-current protection. This is a simple but reliable device based one of the
oldest integrated voltage regulators of them all - the LM723.
Notes
R2 sets the output voltage. The maximum current is determined by the value of R3: the over-current
protection circuitry inside the LM723 senses the voltage across R3 and starts shutting the output stage off
as soon as this voltage approaches 0.65 V. This way the current through R3 can never exceed 0.65/R3,
even if the output is shorted.
C3 and C4, both ceramic, must be placed as close as possible to the integrated circuit, because the LM723
can be prone to unwanted oscillations. It is not an overkill to solder them directly (and very carefully) to
the pins of the IC. All other connections should also be kept short.
The LM723 works with input DC voltages from 9.5 to 40 V and the IC itself can source some 150 mA if the
output voltage is not more than 6-7 V below the input. When an external pass transistor is used (in the
usual emitter-follower mode), the base-emitter junction of T1 represents a significant resistance and the
integrated circuit's output stage is relatively lightly loaded. All the current drawn by the load passes
through T1 and it dissipates an amount of power that is directly proportional to the current and the
difference between the input and the output DC voltage.
542
Finished project
The plastic box is only 160x140x60 mm, yet everything found its place in it somehow. Both meters are
second-hand items, but properly shunted, with new face plates and freshly calibrated dials.
Specification
Output (approximate values):
Vmin = (R4 + R5) / (R5*1.3)
Vmax = (7.15 / R5) * (R4 + R5)
Imax = 0.65/R3
Max. Power on R3: 0.42/R3
Min. Input DC Voltage (pin 12 to pin 7): Vmax + 5
Parts List
B1 40V/2.5A
C1 2200uF (3300uF even better)
C2 4.7uF
C3 100nF
C4 1nF
C5 330nF
C6 100uF
D1 Green LED
D2 1N4003
F1 0.2A F
F2 2A M
IC1 LM723 (in a DIL14 plastic package)
R1 1k
R2 Pot. 5k
R3 0.56R/2W
Regulated DC power supply
Description
This is a Regulated DC power supply with short circuit protection and with current limiter.
Notes
This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around
20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of
20A has been added.
The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the
lower power dissipation.
The rectified current will be "ironed" by C1, whose capacity should not be less than 40.000uF, (a golden
rule of around 2000uF/A), but we recommend 50.000uF. This capacity can be built up by several smaller
capacitors in parallel.
The base of this design is a simple 12V regulator (7812). The output voltage can be brought to desired
value (here 13.8V) by two external resistors (R5 and R6) using this formula:
U= 12(1+R5/R6)
The low currents (here 15mA) will keep the 7812 in its regular function. As soon as the current rises over
15ma, the voltage drop on R4 will "open" the Q3, actually handling the high output current. This is a PNP
539
transistor (Ic > 25) and current amplification factor of at least 20. The one that has been tested and
proven here is the 2N5683.
The current limiting resistance RL, for the maximum output of 20 Amps should be 0.03 Ohms, rated at
least 15W. You can use the resistance wire or switch several resistors in parallel, totaling the
resistance/power values. Values for other currents can be calculated by the rule:
RL=0.7/Imax
The RL and Q2 (3A PNP such as BD330) form a short circuit automatic fuse. As soon as the maximum
current reaches 20Amps, the voltage drop over the resistor RL will open Q2, and thus limit the B-E Current
of Q3. Parallel to Q2 is Q1, which lights the LED 1 whenever the current limiting circuit is active. When the
fuse is active, the Q2 bridges the R3, so the full current would flow through the IC1, and damage it.
Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1
without any cooling aid.
The LED 2 will light up every time the PSU is switched on.
There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current
source for smaller currents.
This circuit is very simple too. You will notice that there is no current sensing resistor. But it is really there,
in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the
source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds
over the resistance Rds rises very slowly in the beginning, but very fast after the knick. This means, that
before the knick the FET behaves as a resistor but after it, works as constant current source.
The D2, R3 and B-E connection of the Q4 will sense the Uds voltage of the FET1. When the voltage rises
enough, the Q4 will shortcut the FET1 gate to mass, and cut the current flow through the FET 1 off.
However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought
up by the voltage divider consisting of R8, Z1, P1 and R9. So the maximum Gate voltage will be the one of
the Z1, and the minimal will be around 3V6. The Z1 voltage (Uz1) will thus determine the max current
flowing through the FET 1. The diagram 2 will show that for 5 Amps the Uz1 should be 5V6, and for
20Amps around 9V6.
540
The Capacitor C4 will determine the “velocity” or the reaction time of the limiter. 100 uF will make the
reaction time to be around 100ms, and 1n will make it 1us. Within the designed limits, the P1 will limit the
current output in the range of 15mA to 20A.
You can use both output simultaneously, but the total output current will be limited by the value of the RL.
This PSU can be built also for higher outputs, as long as the transformer will handle the current
requirements, and you provide sufficient cooling for the Q3.
মঙ্গলবার, ১৭ জুন, ২০২৫
Throttle -simple
এই সার্কিট দ্বারা মোটরের গতি
৫% থেকে ৯৫% পর্যন্ত সামঞ্জস্য করা যেতে পারে। সার্কিটটি একটি FET ব্যবহার করে এবং কোনও হিটসিঙ্কের প্রয়োজন হয় না।
এই সার্কিটটি টকিং ইলেকট্রনিক্স থেকে সম্পূর্ণরূপে একত্রিত মডিউল হিসাবে পাওয়া যায়।
The speed of a motor can be adjusted by this circuit, from
5% to 95%. The circuit uses a FET and no heatsink is
needed. This circuit is available from Talking Electronics
as a fully assembled module.
LASER RAY
এই সার্কিটটি একটি অদ্ভুত "লেজার রে" শব্দ উৎপন্ন করে এবং প্রায় 5Hz গতিতে একটি সাদা LED ফ্ল্যাশ করে: এখানে শব্দটির একটি ভিডিও রয়েছে। একটি বড় স্পিকারের সাথে এটি অনেক ভালো শোনায়।
METAL DETECTOR
This circuit detects metal and also magnets. When a magnet is brought close to the 10mH choke, the output frequency changes. The photo shows the circuit made by a reader
সোমবার, ১৬ জুন, ২০২৫
শুক্রবার, ১৩ জুন, ২০২৫
শনিবার, ৭ জুন, ২০২৫
রবিবার, ১ জুন, ২০২৫
Single Transistor FM Transmitter Design
In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. Throughout the world, the broadcast band falls within the VHF part of the radio spectrum. Usually 87.5 - 108.0 MHz is used to transmit and receive the FM signals. Designing and assembling an FM transmitter is a difficult task. The Note given here explains how a simple FM transmitter is designed and assembled. Design Considerations The performance of an FM transmitter depends on two important aspects. 1. Tuning of the FM transmitter to the desired frequency. Even a slight change in the coil specification or slight change in the variable capacitor value can shift the harmonic frequency instead of the 88-108 MHz FM band. 2. Length of the Antenna used to transmit the frequency. The important parameters for the optimum performance of an FM transmitter are : 1. Transmitter frequency, output power and range of transmission. 2. Antenna length. 3. Coil diameter, length, number of turns and gauge of the wire used for coil winding. The circuit diagram shown below is that of a Single transistor FM transmitter with a range of 30 50 feets and 100 – 125 milli watt output.
The design details of each component are as follows. 1. Condenser MIC The condenser MIC is used to pick up the sound signals. The diaphragm inside the MIC vibrates according to the air pressure changes and generates AC signals. Variable resistor VR1 adjusts the current through the MIC and thus determines the sensitivity of MIC. The condenser MIC should be directly soldered on the PCB to get maximum sensitivity. Sleeving the MIC inside plastic tubing can increase its sensitivity enormously. 2. Decoupling Capacitors C1 is the first decoupling capacitor impedes the different frequencies of speech signals. C1 modulates the current to the base of transistor. The 4.7 uF capacitor isolates the microphone from the base voltage of the transistor and only allows alternating current (AC) signals to pass. A large value capacitor induces bass (low frequencies) while a low value one gives treble (high frequencies). Capacitor C2 (0.01) act as the decoupling capacitor. Capacitor C3 across the transistor T1 keeps the tank circuit vibrating. As long as the current exists across the inductor coil L1 and the Trimmer capacitor, the tank circuit (Coil-Trimmer) will vibrate at the resonant frequency. When the tank circuit vibrates for long time, the frequency decays due to heating. Presence of the capacitor C3 prevents this decay. A capacitor between 4 and 10 PF is necessary. 3. Resistors Variable resistor VR1 restricts the current through the MIC. The voltage divider R1 and R2 limits the base current of T1 and R3 forms the emitter current limiter. The given values are necessary for the 2N 2222A transistor. 4. Transistor 2N 2222A is the common NPN transmitter used in general purpose amplifications. It has maximum power rating of 0.5 Watts. Over powering of 2N 2222A can generate heat and destroy the device. So maximum power output should be around 125 milli watt. Pin assignment of 2N 2222 A is 1 Emitter - 2 Base - 3 Collector (EBC) from the front side (Flat side on which the number is printed). 5. Inductor Coil The inductor used in the circuit is a hand made coil using 22 SWG (Standard Wire Gauge) enameled copper wire. The length, inner diameter, number of turns etc are the important parameters to be considered while making the inductor. Then only the inductor resonates in the 88-108 band FM frequency. For this circuit, the coil radius was selected as 0.26 inches (outer diameter) and 0.13 inner diameter. Coil can be wound around a screw driver (with same diameter) to get a 5 turn coil of 0.2 inch long. Remove the coil from the screw driver and use the 5 turn Air core coil. Remove the enamel from the tips and solder close to the transistor. The inductance of the coil can be calculated using the formula L = n2 r2 / 9r + 10 x Where r is the inner radius of the coil, x is the length of the coil and n, number of turns. The resulting value is in Micro Henry. 6. Trimmer capacitor A small button type variable capacitor with a value of 22 pF can be used to adjust the resonant frequency of the tank circuit. The variable capacitor and the inductor coil form the Tank circuit (LC circuit) that resonates in the 88-108 MHz. In the tank circuit, the capacitor stores electrical energy between its plates while the inductor stores magnetic energy induced by the windings of the coil. The resonant frequency can be calculated using the formula f = 1 / 2 x √LC = Hz Where f is the frequency in hertz, x is the coil length, C is the capacitance of trimmer in Farads, and L is the inductance of coil in Hendry. Tank Circuit Every FM transmitter needs an oscillator to generate the radio Frequency (RF) carrier waves. The name 'Tank' circuit comes from the ability of the LC circuit to store energy for oscillations. The purely reactive elements, the C and the L simply store energy to be returned to the system. In the tank (LC) circuit, the 2N 2222 A transistor and the feedback 4.7 pF capacitor are the oscillating components. The feedback signal makes the base-emitter current of the transistor vary at the resonant frequency. This causes the emitter-collector current to vary at the same frequency. This signal fed to the aerial and radiated as radio waves. 7. Antenna A plastic wire or Telescopic aerial can be used as antenna. The length of the antenna is very important to transmit the signals in the suitable range. As a rule, the length of the antenna should be ¼ of the FM wave length. To determine the length of antenna, use the following equation. By multiplying the Wave frequency and wave length will give the speed of light. Speed of Light = Frequency of Oscillation x Wavelength = in Kms/ Sec Wave length = Speed of light / Frequency = in meters Antenna length = 0.25 x wavelength = in meters By using this formula it is easy to select the antennal length. For the circuit mentioned above, a 25-27 inches long antenna is sufficient. Assembling and Testing The circuit can be assembled on a Dot type common PCB or Perf board. The following tips should be considered while assembling the circuit 1. Assemble the components as close as possible, especially the transistor, trimmer and coil to prevent unwanted oscillation. 2. Lead length of capacitors, resistors, transistor should be as small as possible. 3. Solder the MIC directly on the PCB ( use the trimmed leads of the resistors to connect MIC) 4. Observe the polarity of MIC. 5. Check the pins of 2N 2222 A. The pin assignment is E-B-C (Emitter – Base – Collector) from the front side (Flat side on which the number is printed). 6. Coil should stand horizontally above the Emitter of transistor. 7. Coil should be closely wound. How to test After assembling the circuit, connect 9 volt battery. A battery operated FM pocket radio is necessary for testing. AC powered FM players will give lesser performance than the battery powered FM receivers due to noise. Tune the FM receiver to a “Dead Air space” (around 108 MHz where there is no station). Place the FM radio 2 feet away from the transmitter. Gently tap on the MIC. If the tank circuit is properly tuned, tapping sound will be heard in the radio. If no sound is heard, slightly pull the coil to separate the windings. Adjust the shaft of the Trimmer slowly with a preset screwdriver. Check again. If the sound is clear, move the FM radio and assess the range. Try again by adjusting the trimmer and position of aerial of both transmitter and FM radio. If the sound clarity is good and there is sufficient range, stick the coil with nail polish or glue to avoid frequency change. The FM transmitter is ready to use.