Free Circuit Diagram

Metronome is very important tool if you studying music playing. There are mechanical metronome device in the past, but today, electronic metronome is much more popular since it can be very simple, compact/small, reliable, and also has the most interesting feature: cheap. Here is one example of the electronic metronome schematic:

Parts:

C1 1 uF [...]

A phase control circuit can be used to control the power delivered to an AC load. The phase control circuit control the AC waveform, cutting the cycle to give full cycle, half cycle, zero cycle, or somewhere in between. You can say this circuit is similar to a dimmer circuit, but the switching is synchronized [...]

This sine wave generator is adjustable between 15 Hz to 150 kHz. The circuit is basically a Wien-bridge oscillator, with multiple capacitor selection. Here is the schematic diagram:

A stereo 10k potentiometer is used to control the frequency. The dashed line connecting these two potentiometers show that both potentiometer has single axis.

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 the transistor if [...]

The Battery Charger Circuit
This lead acid battery charger circuit design is very simple and smart.  I call it a smart battery charger design because it uses only few components to support many features.  Here is the schematic diagram of the circuit:

This circuit is suitable for a general purpose lead acid battery charger, or for a [...]

Controlling the speed of three phase ac motor is done by controlling the frequency of the power line supply,  since the motor is synchronized with the line frequency. Three phase ac motor speed controller is actually nothing more than three phase sine wave power inverter with variable frequency. The three phase power inverter is a [...]