hey everyone,
i'm new in all arduino buisness.
i want to build a tool that will check up to 128 pins plug and says:
I assume there is a 128 pin socket as well, that gives you 256 lines to test for continuity and shorts.
That will require 32 shift registers which is a lot. While it is only a medium level project it is not one for a beginner. Scaling up often brings its own problems.
You will need 16 output shift registers and 16 input ones, a UNO will suffice and any key pad and LCD.
- if the wire is short
- if there is a disconnection in the wire
- if the wire is shorted to another wire
Please define the difference between #1 and #3.
Are we to assume that you want to know which wire(s) is bad so you can repair it?
Do you also need to know which end of the wire is bad?
Dejavu
128 wire = 16 shift-out and 16-shift in with pullup resistors, not too unreasonable.
Shift-out - pull 1 output low at a time, check that corresponding input goes low and that no others do.
Test confirms continuity of 1 line and no shorts to other lines.
Commit 4 pins to output shift register/input shift register.
2 pins for serial LCD
http://www.newhavendisplay.com/serial-displays-c-253.html
Browse around, many of the other displays support serial also, they just cost more.
Or go with SPI interface, just need another chip select pin.
7 or 8 pins pins for 12 or 16 button keypad.
2 pins for serial monitor for initial debugging.
Leaves 4-5 pins free on an Uno for other stuff - alarm sound, flashing light, etc.
Note as in the other recent discussion on this matter, that you need to use open-collector outputs (or diodes) on the output shift registers in order to avoid contention in the actual case of a shorted test device.
CrossRoads:
Commit 4 pins to output shift register/input shift register.
Interesting point - you can shift next output register value into the shift register simultaneously with shifting the current value from the input register.
Exactly - SPI is wonderful.