Do you know what the HSETI PCB for? Well, it is a small and simple application for the Atmel AT89C2051 microprocessor, with a 20 pin 8051 variant and FLASH program memory; it’s making this HSETI PCB unique from other PCB boards.

Basically, the board is consisting with two chips, the CPU and a driver/buffer.

If you refer to the diagram below, you’ll find that in the central to the board are the two ICs: The AT89C2051 (in an IC socket) and a ULN2803 driver. Since the bank of resistors to the right of the ULN2803 is primarily and it’s for limiting the current through LEDs, thus they’re will be driven directly from the outputs.

As a result, you may want to use another value instead of the 27 ohm that shown on the circuit. Beside that, the circuitry to the left of the CPU is primarily for the light sensor; this is just a simple Darlington phototransistor, sensitivity pot and switch transistor.

Since this project doesn’t need so many expensive components, thus it won’t cost you too much of money on it! Hope you guys will enjoy this fun project…

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