This is Small DC Motor Speed Regulator It keeps permanent magnet motor running at constant speed regardless of load .Reverse engineered circuit diagram of a motor speed regulator out of a portable pocket tape recorder containing a single motor for all functions. This circuit works amazingly well, keeping the motor speed constant regardless of shaft load and battery voltage. source

This is an actual reverse engineered circuit diagram of the one transistor circuit most commonly used to drive Permanent Magnet DC motors in childrens’ toys. This type of circuit almost always uses the 625mW version of the ubiquitous 8050 or 8550 transistor. It is vital to note that there are two different varieties of each of these two transistors, and although they are often stamped with the same part number, they are not interchangeable because one is a 625mW part with a higher VCEsat, while the other is a 1W part with a lower VCEsat.source

This is DC motor speed control based on PIC16F867.The circuits use frequency PWM about 10KHz which does not make a noise in the motor.This project can drive 1 Amp motor current without over heat.The motor speed controled by potentiometer which is connected to ADC input pin.source