This uses the LM324, a 14-pin DIL IC containing four individual op-amps and running off a single-rail power supply.Two sections of the quad op-amp form a triangle-wave generator, but now the third section is used as a low-gain amplifier, bringing the trough of the wave to just above zero volts and the peak to about 10v.source

Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor. source