Free Circuit Diagram

This inductance meter is actually an adapter to your digital voltmeter (DVM). Using this circuit now your voltmeter is capable of measuring inductor value. Inductance meter is very helpful in designing switch mode power supply, since its often needed  to wind the coil by hand and measure the inductance fro trial and error to get [...]

This capacitance meter circuit is similar with previous meter circuit, but it uses transistors rather than logic gates. Here is the schematic diagram: You can see the circuit uses pnp transistor, you can use almost any pnp transistors with frequency bandwidth og 100MHz and collecttor current handling capability of 100 mA to replace [...]

Capacitance meter can be very helpful in identifying old components where its mark has been erased or became unreadable. Such instrument can be quite expensive, but fortunately we can build it easily with much lower cost. The capacitance meter described here can measure any capacitor between 1pF and 10uF. Here is the schematic diagram of [...]

pH Meter Circuit pH meter measures the voltage (the EMF, electromotive force) generated by the pH electrodes (the sensor) to show the hydrogen concentration in pH scale. Basically, a pH meter is nothing more than a pH probe/sensor with high impedance voltmeter that measures the generated voltage at the pH probe. To measure the [...]

This instrument is very useful for radio frequency (rf) engineer and hobbyist, especially when he/she has to adjust the final rf transmission. Setting up an antenna impedance matcher is one of the example. Here is the schematic diagram of this rf meter circuit: The circuit use only one transistor (MPSA18) as the [...]

This audio frequency meter uses 555 IC as a monostable multivibrator (one-shoot trigger). A monostable multivibrator can act as a frequency-to-voltage converter because it produce a fixed pulse width, with the repetition rate/density is proportional to the triggering input frequency. Here is the circuit’s schematic diagram: For resistor R1, because it set the [...]