The scenario
A battery-powered stirring plate needs a clean 0-300 Hz adjustable rectangular drive for its electromagnet without a microcontroller, using only discrete parts and a 4.2V Li-ion cell.
What is in this drawing
Read the decisions behind it.
01
Use a two-transistor astable multivibrator with dual 1M pots for symmetric adjustable frequency
02
Switch the inductive stirrer coil with a low-side NMOS and add a flyback diode
03
Power from a 4.2V Li-ion battery with input switch and decoupling
When a simple, low-cost analog pulse source must drive a small solenoid or electromagnet with manually tunable frequency and minimal standby parts.
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