By Josh Bensadon, Email: joshbensadon@yahoo.com
This circuit provides 10 outputs from the PC comm line. It uses an addressed communication scheme of 4 bytes.
Communication from PC is at 9600,N81
Message length = 4 BYTES (fixed)
| Byte | Logic | Description |
| 1 | 000a aaaa | Address (top 3 MSBs must be 000) Address, 1-30 recomended since this will reserve address 0 and 31 |
| 2 | 001c bbbb | 5 output bits |
| 3 | 010c cccc | 5 output bits |
| 4 | 011x xxxx | CRC (top 3 MSBs must be 011) XOR check sum of bytes 1-3 |
The outputs are TTL level and can directly drive an LED or can be amplified with a transistor to drive a low voltage incadesent lamp (up to 24VDC). A IC driver chip like the ULN2803 (8 transistors) or ULN2003 (7 transistors) can be directly connected to the PIC chip. These driver chips have the base resistor built in, so it makes a neat and simple circuit. They also have built in Reverse EMF diodes, but I prefer external ones mounted as close as possible to any coil being driven.
Software at the PC will control the outputs. Software will be provided soon, as a DOS program. Any old 486 running dos can use it.
The normal disclaimer applies, I will not be responsible for any damages as a result of this circuit. If you use it, it is at YOUR OWN RISK.
You can get all the parts from www.digikey.com
The programmed PIC chip is available for $4.50 US and shipping, just send me an email for payment instructions.
Josh Bensadon
Josh's files for this can be download here: PCAuto.zip