Magnetic-Radiation Remote-Control

 Short-range 35KHz operation, single-channel unit 

Simple circuitry, no outer antennas required

 

Transmitter circuit diagram: 

Transmitter parts: 

R1 68K 1/4W Resistor 

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)

Receiver parts: 

R1,R3 1M 1/4W Resistors 

R2,R4 47K 1/4W Resistors 

R5 330K 1/4W Resistor 

R6,R7 68K 1/4W Resistors 

R8 180R 1/4W Resistor 

R9 100R 1/4W Resistor 

C1 470pF 63V Ceramic Capacitor (See Notes) 

C2 10nF 63V Polyester or Ceramic Capacitor 

C3 100µF 25V Electrolytic Capacitor 

C4,C5 100nF 63V Polyester or Ceramic Capacitors 

C6 1µF 63V Polyester, Ceramic or Electrolytic Capacitor 

D1 5 or 3mm. Red LED 

Q1,Q2,Q3 BC549C 25V 100mA NPN High-gain Low-noise Transistors 

Q4 BD328 30V 800mA PNP Transistor 

L1 700 turns on a 10mm. diameter, 10cm. long ferrite rod. 

Enameled wire diameter: 0.2mm. 

The tap is made after 350 turns, i.e. at the center of the winding 

BZ1 Piezo sounder (incorporating 3KHz oscillator, optional, see Notes) 

RL1 5V DIL Reed-Relay SPDT or DPDT (Optional, see Notes) 

B1 3V Battery (2 x 1.5V AA, AAA or AAAA Cells in series or 1 x 3V Lithium Cell) 

Device purpose: 

This unit can be useful as a short-range, single-channel remote-control. When the pushbutton in the 

transmitter circuit is briefly activated, the LED D1 in the receiver illuminates and an optional beeper or 

relay can be operated. 

Circuit operation is based on a non-modulated 35KHz frequency carrier transmitter, and on a high-gain 

two-stage 35KHz amplifier receiver, followed by a frequency-voltage converter and DC load driver. 

Outstanding features for this design are as follows: 

No outer antenna is required on both transmitter and receiver sections, due to the very low frequency 

operation. The antennas are 10mm. diameter, 10cm. long ferrite rods supporting the coils. 

Unlike Infra-red remote-controls, this unit operates through the walls etc. 

No radio-frequency interference in spite of simple circuitry. 

The receiver operates at ultra-low voltage supply (3V) and standing current (100µA): in this manner it can 

be left in stand-by mode for years before a battery replacement is needed.  

Snags are: the short-range operation (about a medium-sized apartment), the high number of windings for 

the coils and the high current drawn by the transmitter. 

Luckily, this latter snag is compensated by the fact that only a short pulse from the transmitter is needed 

 to operate the receiver. Therefore, if the transmitter is not operated continuously, its battery should last 

long. 

    Notes: 

 Q2 in the transmitter should have a small heatsink.   

A good compromise is to use a 6V supply for the transmitter (four 1.5V AA cells in series). 

In this case   current drawing is 300mA.   

Needing a shorter range operation, Q2 in the transmitter can be omitted. 

Therefore, the emitter of Q1 will   be connected to the tap of L1 coil. 

In this case the circuit could be powered by a 9V PP3 alkaline battery,   drawing about 100mA current.   

The receiver must be tuned to the transmitter frequency. 

Starting with a 470pF value for C1, you should   

try to modify its value by means of small capacitors wired in parallel to it, 

in order to obtain the highest AC   voltage output at Q2 or Q1 collector (best measured with an oscilloscope).

 C1 value might vary from about   400 to 800pF.  

 Do this setup with transmitter placed 4-5 meters away from receiver.

 During setup it is wise to temporarily   

connect the transmitter to a 6 or 9V regulated power supply, in order to save batteries.  

 A small DIL 5V reed-relay was used in spite of the 3V supply of the receiver.

 Several devices of this type   

were tested and it was found that they switch-on with a coil voltage value comprised in the 1.9 - 2.1V   range.

 The coil resistance values varied from 140 to 250 Ohm.

IR Remote Control Extender Circuit

Description: 

This is an improved IR remote control extender circuit. It has high noise immunity, is resistant to ambient 

and reflected light and has an increased range from remote control to the extender circuit of about 7 

meters. It should work with any domestic apparatus that use 36-38kHz for the IR carrier frequency. Please 

note that this is NOT compatible with some satellite receivers that use 115KHz as a carrier frequency. 

Circuit diagram 

Notes: 

The main difference between this version and the previous circuit, is that this design uses a commercially 

available Infra Red module. This module, part number IR1 is available from Harrison Electronics in the UK. 

The IR module contains a built in photo diode, amplifier circuit and buffer and decoder. It is centerd on the 

common 38kHz carrier frequency that most IR controls use. The module removes most of the carrier 

allowing decoded pulses to pass to the appliance. Domestic TV's and VCR's use extra filtering is used to 

completely remove the carrier. The IR1 is packaged in a small aluminium case, the connections viewed 

from underneath are shown below: 

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 

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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. 

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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. 

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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. 

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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.

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

FLASHING RAILROAD LIGHTS

 This circuit flashes two red LEDs for a model railway crossing.

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