Wiring Schematic Diagram

Most good bench power supplies include a form of overvoltage protection, but for those power supplies or for other applications where over voltage protection is required, a simple over voltage crowbar circuit can be built. It uses just four components: a silicon controlled rectifier or SCR, a zener diode, a resistor and a capacitor.

The SCR over voltage crowbar or protection circuit is connected between the output of the power supply and ground. The zener diode voltage is chosen to be slightly above that of the output rail. Typically a 5 volt rail may run with a 6.2 volt zener diode. When the zener diode voltage is reached, current will flow through the zener and trigger the silicon controlled rectifier or thyristor. This will then provide a short circuit to ground, thereby protecting the circuitry that is being supplied form any damage.

However it is necessary to ensure that the power supply has some form of current limiting. Often a fuse is ideal because the SCR will be able to clamp the voltage for long enough for it to blow. The small resistor, often around 100 ohms from the gate of the thyristor or SCR to ground is required so that the zener can supply a reasonable current when it turns on. It also clamps the gate voltage at ground potential until the zener turns on. The capacitor is present to ensure that short spikes to not trigger the circuit. Some optimisation may be required in choosing the correct value although 0.1 microfarads is a good starting point.

This circuit is used to indicate the amount of water present in the overhead tank. Not only that, but this circuit also gives an alarm when the tank is full. CD4066 is used to indicate the level of the water through LEDs.

The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs. When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON. As the water continues to fill the tank, the LEDs2 , 3 and 4 light up gradually. The no. of levels of indication can be increased to 8 if 2 CD4066 ICs are used in a similar fashion. When the water is full, the base of the transistor BC148 is pulled high by the water and this saturates the transistor, turning the buzzer ON. The SPST switch has to be opened to turn the buzzer OFF. Remember to turn the switch ON while pumping water otherwise the buzzer will not sound!

This is a volt meter circuit based on LM324 OpAmps chip. A bargraph generator is nothing more than a slack-handful of OpAmps, all thrown into a single chip. It is cheaper to use the LM324 and put in the few extra components needed.

R1 to R8 down the left all form a voltage divider from the 7.5v Zener diode. The resistors give me taps of 0.5v, 1.5v, 2.5v, 3.5v, 4,5v, 5.5v, and 6.5v. The top of the zener gives me the eighth voltage: 7.5v. These reference voltages are all connected to the negative-acting input of each OpAmp, and all the positive-acting inputs are gathered together for a common input. With 0v on the +ve inout, the output voltage of avery OpAmp is 0v.

If the input voltage lies between 0v and 0.5v then no LED lamps will light. If the input voltage rises to between 0.5v and 1.5v (1v +/-0.5v) then the first LED will light when the first OpAmp +ve input exceeds the -ve input threshold. In this way the LEDs all form a nice bar-graph display in 1v steps, +/- half a volt.

The A-B-C links should be in the A-B position for a normal bar-graph display, when each LED succesively lights as the voltage rises. With +4v input there will be four LEDs lit. If you fit the links in the A-C position then only one LED will light for each voltage step, to give a moving dot display. The top (last) link should always be in the A-B position for both modes.


This Op-Amp Voltmeter Circuit From www.sm0vpo.com:800

If you want a 1.5V to 5V Step-Up Converter here is a simple circuit using LT1073 from Linear Technology. The LT1073 is a versatile micro-power DC / DC converter. The circuit requires few external components to deliver a fixed output of 5V.

1.5V to 5VDC Converter Circuit by LT1073

LT1073 Pinout

The very low minimum supply voltage of 1V allows the use of the LT1073 in applications Nowhere the primary power source is a single cell. An on-chip auxiliary gain block cans function as a low battery detector or linear post-regulator.The LT1073 is good idea, it Used for dc to dc converter.Average current drain of the LT1073-5 Used as shown in the Typical Application Circuit below is just 135mA unloaded, making it ideal for applications Nowhere Long battery life is Important. The circuit shown cans deliver 5V at 40mA from an input as low as 1.25V and 5V at 10mA from a 1V input.

This is a circuit which built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier.

Turn On Relay Delay Circuit for power amplifier

The idea of the circuit is wait around 5 seconds ofter the power up until the speakers are switched to the amplifier output to avoid annoying "thump" sound from the speakers. Another feature of this circuit is that is disconnects the speaker immediately when the power in the amplifier is cut off, so avoiding sometimes nasty sounds when you turn the equipments off.

This circuit is not the most accurate and elegant design, but it has worked nicely in my small home-built PA amplifier. This circuit can be also used in many other applications where a turn on delay of few seconds is needed. The delay time can be increased by using bigger C2 and decreased by using a smaller C2 value. Note that the delay is not very accurate because of simplicity of this circuit and large tolerance of typical electrolytic capacitors.