The following parts are needed if you use the Olimex board as a starting place

I believe this is finally correct. You may only need two of the 0.1 uf bypass caps but they are cheap so I recommend we be safe and add one to the 16F88.



Quantity Part Desc. Notes
1 Olimex Board Prototype board (16F88 20 Mhz)
3 0.1 uf C3, C6, C7 - Monolithic capacitors
2 1N4148 D3, D4- Signal diodes
1 color LED D1 - Receive data indicator
1 color LED D5 - Transmit data indicator
1 10k R7- resistor
4 1k R1, R5, R8, R11 - resistors
2 2k R9 - resistor
1 3.9k R3 - resistor
1 8.2k R4 - resistor
1 or 2* 100k R6 - resistor
1 or 2* 470 R10 - resistor
1 10K variable R12 - miniature potentiometer
1 2N2222A Q1 - PNP transistor


* There is a suggested addition to Bob's original circuit that would add another 100K and a 470 ohm resistor.  They add a little hystereses to the input comparator circuit. I recommend these changes and will add them to my unit but they are not required. I will describe how the additional resistors are wired into the circuit an a few days.