Mutchus

Four µ741 op-amps are used here to measure the voltage ranging from 3V to 12V DC. The voltage measured is displayed on eight LED s. The inverting inputs (pin 2) of IC1 through IC4 are supplied with regulated 12V DC through voltage dividers R1 through R4. So the inverting input of each op-amp forms the reference voltage. The non-inverting inputs (pin 3) of the op-amps are tied together and connected to the input terminals. The voltage to be meaured is fed to these input terminals. When the input voltage exceeds the reference voltage of any of the op-amps, its output goes high, making the corresponding LED s to glow. This circuit is designed to measure 3V, 6V, 9V and 12V DC. For instance, when the input voltage is 3V, LED 7 and LED8 glow. When the input voltage is 12V, all the LED s glow. Note. You can use a quad device such as LM324 instead of µ741 IC s. Circuit Diagram:   

Normally we often encountered the frequency meter can be used in speed sensor, tachometer, measurement or signal recurring. This frequency to voltage converter (FVC) can be used to change the voltage into a digital or analog tachometer. Circuit that consists of three blocks. The first block is squarer, the input signal to a square wave. This block is protected from high input voltage up to 400V, but remember this only works if the value of capacitor C1 is for 400V. Input Impedance around 560k, so it is safe to connect the ignition pick-up coil in parallel with the CDI (capacitor discharge ignition) circuits without a problem. Supply is protected from voltage spike by Zener diode D3. Here is a schematic picture: The second block is retriggerable monostable multi vibrator. Monostable multi-vibrator is to convert fixed width pulses to provide output, the voltage output of the average will depend on the duty factor pulses input / waveform, but only depends on the input frequency. Pulse wid...