1.24.12 Interfacing to a Microcontroller

In this circuit, I used a 2N3904 transistor and a 470ohm resistor with the PICAXE microcontroller and an 200mA incandescent bulb as an output device.  The light flashes on and off and the transistor was hot.

For the next circuit,  I replaced the 2N3904 transistor with a TIP 41 transistor.  The light flashed on and off again, but this time, the new transistor stayed cool.  I then replaced the 470ohm resistor with 2.2Kohm resistor and the light remained bright.

The next circuit consisted of a darlington configuration (the 2N3904 acts as a signal transistor providing 300mA to the TIP 41 which acts as a power transistor with a 1K resistor.  This configuration provides a high Gain.

  In the next circuit, I replaced the two transistors with an equivalent darlington TIP 122 transistor.  The light is just as bright and the TIP 122 remains cool.

Using the same circuit, I replaced the incandescent bulb with the motor for the eyes of the toy I 'hacked' and added an emf suppression 1N4001 diode in parallel for the coil of the motor.