Design Overview: As I said in the last blog I am going to use an Arduino Mega 256 not for its I/O capabilities, but for its memory size. Getting to 50 pins is really 100 pins! Ouch. 
The only way I can achieve this is to use 4 16 bit I/O expander. Enter the MCP23017 which has a High-speed I2C
interface (100KHz, 400KHz, 1.7MHz) and I can have eight (8) devices on this bus at one time. But I will only use 2 expanders on the input, and two more on the output. I will also include an I2C interfaced LCD panel for display and control. The Arduino itself will read the buttons to scroll through the cables, or to enable the flying probe. I can interface the tester to my PC via USB or Ethernet (later). Well for better or worse, here it is.
UPDATE - 6 JUN 2021
On one side I will have 3 MCP2317 as to also allow me to use a DB-37. and BTW it is just as easy to add the DB-37 to both sides. 
| Device | Unit | Pins |
| MCP23017 | 1 | 1 - 16 |
| " | 2 | 17 - 32 |
| " | 3 | 33 - 37 |
Top Comments