The electronics

Mechanics Built on an experimentation board (Veroboard) and housed in a wooden box. 
Microcontroller mounted in a socket to faciliate easy removal for reprogramming.
Power supply 12 V 400 mA AC/DC adapter.
Microcontroller Microchip 16C84 or 16F84. Assembler for this controller is available from Microchip free. 
Many programmers with software for this controller are available. You can buy them cheap through the internet or build yourself. I use a home built programmer connected to and powered from the PC through a serial port.
Microcontroller 
peripherals
  • Button input to start fan and set test mode. I have two of these connected in parallell. One outside the electronics case, and one inside on the circuit board used during development.
  • LED output. Once more one inside and one outside the box. It indicates when a button press will start the fan. Every 2-minute periode there is a 110s interval when a button press will start the fan. If you do not press the button, the fan will start automatically at the end of the period. 
  • Fan control output. Drives 12V 250 mA fan motor.
  • Magnet control output. Drives 12V 250 mA electromagnet to let one ball into plexiglass tube.
  • Infrared detector input. An infrared diode transmitter and detector detects when the ball is halfway up the tube. This information is used to stop the fan as early as possible.
 
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Last modified 15.05.98