Ribbon Cable Testing

Bit of a newbie to this. I need to create a ribbon cable tester, have found a few bits n pieces on the forums, but ideally need how to check between the pins for shorts. 25 way IDC "D" type, ribbon cable so how to determine a short, say between pins 1 and 2 or pins 1 and 14, ie pins next to each other as can short if IDC "D" type not crimped correctly. "D" type either end, cables approx. 30cm length.
Looking at using a 4 x 20 or 4 x 40 LCD to display results, pass / fail / shorted pins.
Any help would be useful.

Using ribbon cables for many years I see them as very reliable and safe provided that precision is used when applying the connectors. That is number one. Then I have never felt needing testing the cables.

Of course, if You face trouble with cables assembled somwhere else, change Your supplier.

To fully test a 25 ribbon cable You need 25 outputs and 25 inputs, or maybe 50 inputs.
What's is Your reason for this project?

We make the ribbon cables "in house" for a customer and we have been testing the cables with a meter. We don't often get issues with faulty cables, but be nice to properly test and a lot quicker, but instead of shelling out several hundred quid for a dedicated ribbon cable tester, decided to make one to facilitate this test, easier to test, connect cable and press a button and test.
Have got a Mega 2560 to play about with.

Okey, thats gives Your project an other dimension which I have experience of.

25 cables to test... Shorts beween cables, open circuit... Thats mainly what is to detect.

I am not familiar with the Mega 2560. Check the numer of I/O pins it have. Having 25 outputs and 25 inputs would do. You can always use multiplexers for input or output to enlarge the I/O capacity.
I would recommend a 10 -100 kOhm serial resistor on the outputs in case of a short to the not active neighbour. That wil give detectable levels for the inputs.

What is Your target yield?

You only need 25 pins, no need for 50. One connector: all 25 pins connected to GND. Second connector: all 25 pins connected to individual pins. Set those pins to INPUT_PULLUP. Any pin that now reads HIGH is not connected, i.e. that wire is broken. Any pin that now reads LOW is connected, i.e. that wire is good. All 25 pins LOW: cable is good. All 25 pins HIGH: no cable connected at all.

If you want to be able to detect wrongly connected wires, you indeed need 50 pins. One side pins all INPUT, the other side INPUT_PULLUP. Now set one of the pins of the one side to OUTPUT, LOW, and check whether only the corresponding pin on the other side goes LOW. Then that wire is good. If it doesn't go LOW, it's not connected. If other pins go LOW (as well), there's a cross connection.

A few years ago a customer replaced all the cables on a piece of equipment that used fairly strong chemical solutions. The solutions had damaged the cables, over time.

Many of the cables were ribbon cables of various lengths and conductor counts.

The ribbon connectors were all of the "insulation displacement" type and could not fail by shorting, only fail by not making a connection to the conductor in the cable.

The customer did not require cable testing, but I insisted we go through the exercise. I built a tester box with connectors for each end of each type of connector. Powered by a 12 volt PSU. I used LEDs with dropping resistors to turn on when a circuit was properly made. So, only looked for continuity.

The customer also bought the tester!

So, I don't see the need for such a complex testing device or procedure.

Paul

Graham_B , What solution did you go with, if any?

I am trying to build a ribbon cable tester for cables with DB15 connectors. I what to detect opens, and shorts.

I came across this idea: w w w. gadgetronicx. com /idc-ribbon-cable-tester-circuit/
(it doesn't use an Arduino)

Paul_KD7HB , This was my first idea but it will not do good at detecting shorts, which I need. Using the ribbon cable to complete a circuit to turn 15 LEDs on. I got everything I needed and almost was done before realizing that shorts will still turn the LEDs on. So I started looking for a "smart" solution and I have an UNO laying around.

scoopsix:
Graham_B , What solution did you go with, if any?

I am trying to build a ribbon cable tester for cables with DB15 connectors. I what to detect opens, and shorts.

I came across this idea: w w w. gadgetronicx. com /idc-ribbon-cable-tester-circuit/
(it doesn't use an Arduino)

Paul_KD7HB , This was my first idea but it will not do good at detecting shorts, which I need. Using the ribbon cable to complete a circuit to turn 15 LEDs on. I got everything I needed and almost was done before realizing that shorts will still turn the LEDs on. So I started looking for a "smart" solution and I have an UNO laying around.

A properly made connector for ribbon cable and using the correct size ribbon cable means a short is impossible. If you are finding shorts between wires, you have other problems!

Paul

wvmarle:
You only need 25 pins, no need for 50.

Even less. Rather than setting each pin as an output, a 4:16 demultiplexer will turn 4 lines into 15 (and off) of output, and another bit or two could enable two for these (for one bit here, you need either an inverter or paired demux where one has a high and the other a low enable.

you might. be able to use multiplexers with attention to the order you test, assuming your multiplexer is deterministic as to whether the lowest or highest live input is represented.

A Mega will be the easiest and cheapest solution. Add connectors matching the cable mounted connectors, with an adapter sticking into the double row connector for easy reconfiguration to other cable types. Then configure all related pins as INPUT_PULLUP, and test one after another as low output, and check whether exactly those other pins go low which should be connected.