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H Bridge

2. The device

2.3. PWM motor speed control

The motor speed is controlled by a 555 timer circuit. Its output is fed to the gate of the MOSFETs. The speed of the motor is altered by modulating the pulse-width of the output. The duty cycle of the signal is controlled with a variable resistor (potentiometer).

The 555 timer IC is used in astable mode (not monostable because it generates only a single pulse).