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Some types of electronic equipment do  not provide any indication that they are  actually on when they are switched on.  This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains  power  indicator  is  not  required  with  equipment  that  consumes  less  than  10 watts. As a result, you can easily forget  to switch off such equipment. If you want  to know whether equipment is still drawing power from the mains, or if you want  to have an indication that the equipment  is switched on without having to modify the equipment, this circuit provides a solution. One way to detect AC power current and  generate a reasonably constant voltage  independent of the load is to connect a  string of diodes wired in reverse parallel in series with one of the AC supply  leads. Here we selected diodes rated  at 6 A that can handle a non-repetitive  peak current of 200 A. The peak current  rating is important in connection with  switch-on  curr...

One tool that I’ve been missing at my lab at home is function generator. They tend to be a bit expensive, so I haven’t bought one. I thought this might be a good opportunity to try and make one myself. I found a pretty common DDS (direct digital synthesis) chip, called AD9833. Then just strap a USB-enabled AVR micro there and maybe some analog electronics. This board doesn’t do any of the special analog magic to allow for variable amplitude or offset for the signal. The output is fixed to 0-4v. I’m planning to make another completely analog board for adjusting amplitude and offset.

This circuit lets you turn on/off a fan by just directing torchlight or other light toward its light-dependent resistor (LDR). The circuit is powered from a 5V power supply. Preset VR1 and a light-dependent resistor (LDR) work as the potential divider. Normally, the LDR’s resistance is high (20 kilo-ohms) in darkness and low (2 kilo-ohms) in light. This value of high and low resistances varies for other LDRs. Preset VR1 is used for setting the intensity of light, while preset VR2 is used for setting the output time period of IC1. Fan on/off Control by Light Circuit Diagram When light falls on the LDR, the monostable (IC1) triggers at pin 2, making its output at pin 3 from low to high. This low-to-high transition forms a clock for D flip-flop. The D flip-flop is operated in toggle mode by connecting its Q output to D point. The flip-flop output goes to an inverter (N1). The inverter output is fed to the relay driver transistor. When the inverter output is low, diode D1 conducts and the ...

Get the circuit instead of a standard on-off switch. Switching is very gentle. If  we don’t use the PCB, connect unused input pins to an appropriate logic level (‘+’ or ‘-’).  Unused output pins *NEED* be left open!  On the Print Circuit Board this has completed already . One step ’push’ activates the relay, another ‘push’ de-activates the relay. IC1 (the 4069) is a regular Hex-inverter type and is constructed with MOS P-channel and N-channel enhancement mode devices in a single monolithic structure. Alternating On-Off Switch Circuit Diagram : Parts List : R1 = 10K R2 = 100K R3 = 10K R4 = 220 Ohm (optional) C1 = 0.1µF, Ceramic (100nF) C2 = 1µF/16V, Electrolytic D1 = 1N4001 Led1 = Led, 3mm, red (optional) Q1 = 2N4401 (see text) IC1 = 4069, CMOS, Hex Inverter (MC14069UB), or equivalent S1 = Momentary on-switch Ry1 = Relay ) It is going to operate on voltages from 3 to 18 volts, but most applications are in the 5-15 volts.  Although the IC1 4069 contains protection circuitry against...

Build a Electronic Transistor Turns Op Amp On or Off Circuit Diagram . In this circuit When transistor Q1 is switched off, the circuit behaves as a voltage follower. By applying a positive voltage to the emitter of Q1 via a 10 KOhmhm resistor, the transistor is made to turn on and go into saturation. Thus, the lower end of R4 is connected to ground.   Electronic Transistor Turns Op Amp On or Off Circuit Diagram The circuit has not changed into that of a differential amplifier, except that the voltage difference is always 0 V. As long as the resistor ratios in the two branches around the op amp are in the same ratio, the output should be zero. A 47-KOhm resistor is used to null out any ratio errors so that the off attenuation is more than 60 dB. The high common-mode rejection ratio of a 741 enables this large attenuation to be obtained.

This is an On Air indicator , ie an indicator circuit dr RF transmission , very simple and useful for those who like RF . This circuit detects the RF output using a visual indicator , but with some modifications , the LED may be replaced by a relay or any other system that want to trigger when the transmitter is switched on. The output of the transmitter or other RF generator must be connected to this RF input circuit.   Simple Circuit indication for RF Output Transmitters List of components Resistor R1 560Ω eighth Capacitor C1 330pF disc C2 Capacitor 0.1μF disc Diode D1 1N34 or 1N60 D2 LED Transistor Q1 2N3904 or equivalent  If you liked this article,Take a few Seconds to Share this and leave comments