all type circuit

রবিবার, ১৮ জানুয়ারি, ২০২৬

1-10 MINUTE AUTO TURN OFF

This circuit provides an automatic turn-off feature after a time that can be set from 1 minute to 10 minutes by the 470k pot.

WATER LEVEL DETECTOR

This circuit can be used to automatically keep the header tank filled. It uses a double-pole relay.

This is the transistor version of the circuit below. Here is the circuit using a 555:

These are the facts you have to remember. In our circuit, Pins 2 and 6 detect a voltage when water is not touching the probes, due to the 100k resistors.

When water touches the probes, neither pin "detects a voltage." Don't worry about pin 2 detecting 1/3 of rail voltage and pin 6 detecting 2/3 of rail voltage.

In our circuit the pins either detect a voltage or do not detect a voltage.

Pin 2 detects a LOW and pin 6 detects a HIGH. Pin 2 does nothing when it detects a HIGH and pin 6 does nothing when it detects a LOW.

When the water is LOW, as shown in fig 1, both pins 2 and 6 are HIGH and the output of the 555 is LOW.

As the water rises, as shown in fig 2, Pin 6 goes low but nothing happens to pin 3 except the chip "has been prepared via the internal flip-flop" to change when pin 2 goes LOW.

When the water reaches pin 2, as shown in fig 3, this pin "fails to see a HIGH," the output of the chip goes HIGH and the pump turns off. As the water level goes down, as shown in fig 4, pin 2 sees a HIGH but this does not change the 555 as pin 2 only has an effect when it goes LOW.

When the water level goes down further, as shown in fig 5, pin 6 sees a HIGH and because pin 2 is not seeing a LOW, the chip will change states. The output goes LOW

WARNING LIGHTS FLASHER

These two circuits flash two 5 watt to 21watt car lamps. The first circuit uses BD679 Darlington transistors and the second circuit uses a 555. This 12v Warning Beacon is suitable for a car or truck break-down on the side of the road. The key to the operation of the circuit is the high gain of the Darlington transistors. The circuit must be kept "tight" (thick wires) to be sure it will oscillate.

MISSING AUDIO DETECTOR

This circuit detects when audio is not received for about 4 seconds and turns on an alarm.

5 SECS DELAY THEN RELAY ON FOR 4 SECONDS

This circuit waits 5 seconds before turning on the relay for 4 seconds.

MISSING PULSE DETECTOR

This circuit is described on the web as a missing pulse detector. If the 1M pot is turned to zero ohms, it will be damaged when the transistor inside the 555 at pin 7 connects to 0v rail.

MERCURY SWITCH DETECTOR

This circuit is a LATCH CIRCUIT and it detects when the mercury switch is tilted. But it is consuming 10mA while it is sitting around waiting for the mercury switch to make contact. By replacing the 555 with two transistors, the circuit will consume zero current when waiting for the switch to close. Sometimes a 555 is not the ideal choice.

বুধবার, ১৪ জানুয়ারি, ২০২৬

Medium Frequency Amplifier

This circuit, Figure 7, is primarily intended for use over the 1.7MHz to 30MHz range, and will be found to provide consider able gain. RF amplifiers of this kind are generally used to im prove long distance short wave reception, to increase volume, and to reduce second channel interference on the higher fre quencies. To avoid winding coils and permit easy band changing, Denco (Clacton) miniature plug in coils may be used. These are they “Blue” (Aerial) ranges, valve type. The most useful coils will be Range 3, 1.67-5.3MHz, or 580 to 194 metres; Range 4, 5-15MHz or 60 to 20 metres; and Range 5, 10.5-31.5MHz, or 28 to 9.5 metres. Exact coverage depends on the setting of the adjustable cores, and will also be modified if VC1 is of different value. The coils are inserted in a B9A type holder. If only single range is wanted, the coil can be mounted by its threaded end, and leads are then soldered directly to the pins. VR1 is an adjustable aerial input control, as overloading may easily arise with strong signals. R1 and R2 provide the voltage for gate 2, and R3 is for source bias. The drain circuit is arranged for capacitor coupling by C4 to the aerial socket of the receiver. This lead should not be unnec essarily long, as this may cause losses, as well as picking up signals which cause second channel interference. If the lead is screened, it must be no longer than necessary. A 2.6mH short wave sectionalised radio frequency choke will be satisfactory for the frequencies mentioned. Construction is best in a metal case, which can have a hinged lid if plug-in coils are to be fitted. (An alternative, for several bands, is to use switching as shown for Figure 11.) No ganging difficul ties can arise with VC1, which is adjusted for best volume. Second channel interference is caused by signals which are 2xIF frequency from the wanted signals. With a 470kHz interme diate frequency, these offending signals will be 940kHz from the wanted transmission. As a result, interference from this cause is unlikely at low frequencies, but very probable at high frequen cies. Such second channel interference is considerably reduced, or completely avoided, by using a tuned RF stage of this kind, actual results in this direction depending on the receiver IF, and frequencies tuned. A 9v supply is adequate, and current may be drawn from the receiver if convenient. Only about 2mA to 3mA or so will be wanted. The MEM618, 40602, and 40673 will be found satisfactory here

RF AMPLIFIERS AND CONVERTERS

144MHz Preamplifier

This preamplifier can be used with existing 2 metre equipment,

or ahead of the 144MHz converter described later. TR1 is the

40602 or 40673.

Aerial input is to a tapping on L1, and will generally be by

co-axial feeder. In some circumstances a short vertical aerial or

whip may be used and may provide sufficient signal strength. A

high aerial will naturally increase range and many different types

of aerial for 2m reception can be obtained. Alternatively, if a start

is being made on this band, a simple dipole may be constructed.

This can be self supporting, or of stout wire, and can be about

38½in in length overall, with the feeder descending from the cen

tre. Such an aerial will have little directivlty so need not be ro

tated, and can be raised on a light pole or mast.

For 144-146MHz reception, L1 is permanently tuned to about

145MHz by T1. Input is to gate 1, from a second tapping, and R3

with the by-pass capacitor C2 provide source bias. Gate 2 is op

erated at a fixed potential derived from the divider R1/R2. Output

from TR1 drain is to the tapping on L2, which is tuned by T2. For

a narrow range of frequencies such as the 2m Amateur band,

variable tuning is not justified, especially as L1 and L2 do not

tune sharply L3 couples to the existing 2m equipment - generally

a converter working into a lower frequency receiver.

L1 is wound with 18swg or similar stout wire, enamelled or

tinned copper. It has five turns and is tapped at one turn from the

upper end in Figure 4 for G1, and two turns from the grounded

end for the aerial. The winding is 5/16th in in diameter and turns

are spaced so that the coil is ½in long. L2 is wound in the same

way with five turns, but is ¾in long and has a centre tap for the

drain. L3 consists of a single turn of insulated wire, wound over

the lower end of L2.

When building VHF units of this and similar type, a layout per

mitting short radio frequency and by-pass return connections will

be required, and Figure 4B shows a layout for Figure 4. (Note

that TR1 is shown from the top.) A printed circuit can be pre

pared to take the components, or plain perforated board (0.15in

matrix) can be used, wired below. It is convenient to insert pins to

take L1 and L2. A small aluminium box will house the amplifier,

and this allows the co-axial aerial and output sockets to be

mounted as shown.

The screen to divide the box into two sections, to separate

gate 1 and drain coils, can generally be omitted as the layout

does not allow much feedback from L2 to L1. Tapping Gate 1

and drain down L1 and L2 also contributes to stability.

A 12v supply is preferred, but this can be 9v if other equip

ment provides this voltage and is also to supply the amplifier. The

amplifier can be self-contained if a battery is included in the box,

with on-off switch in series.

The bolts MC pass through the board and box, so that they

can provide a ground return, and they require spacers or lock

nuts. (Should it be felt that full details of preparing a printed cir

cuit, or wiring on perforated board, are required, reference can

be made to handbooks No. BP30 and No. BP35, Babani Press.)

Should a resonant dipper be available, or be constructed as

shown later, this will allow L1 and L2 to be set to about 145MHz.

If the coils are made exactly as described, adjustment of T1 and

T2 should give resonance in the 2m band. However, slight

changes in the length of leads, and similar points which arise in

construction, can influence the frequency. So should either trim

mer, be fully open, stretch the associated coil slightly to separate

its turns. On the other hand, if either trimmer is fully closed, com

press the coils to bring the turns nearer together. It is possible to

experiment with the taps, for best individual results, if the coils

are wound with tinned copper wire. Resonance can later be

checked when signals are being received through the amplifier.

To do this, or tune with no dipper, adjust the trimmers (and coils if

necessary as mentioned) for best volume

মঙ্গলবার, ১৪ অক্টোবর, ২০২৫

long range video transmitter circuit #circuitlove #toolsTutorial

AUTOMATIC GARDEN LIGHT

AUTOMATIC GARDEN LIGHT This circuit automatically turns on and illuminates the LEDs when the solar panel does not detect any light. It switches off when the solar panel produces more than 1v and charges the battery when the panel produces more than 1.5v + 0.6v = 2.1v

PHONE TRANSMITTER - 3

PHONE TRANSMITTER - 3 see also Phone Bug (101-200 circuits) This circuit has poor features but you can try it and see how it performs. It uses a PNP transistor and requires a separate antenna. It also has a supply of less than 1.9v, via the red LED. It would be better to put 2 LEDs in series to get a higher voltage. It is activated when the phone is picked up.