Is it possible to make a ribbon cable tester with only passives? - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: November 10, 2019, 08:08:37 am
content: I need (want) to make a ribbon cable tester for 16 pin IDC ribbon cables....they are super expensive and the only affordable one i found is for 40 pin cables. That is fine but not what i need.https://riddledtv.com/arcade/images/40pin_Cable_Tester_800.jpgWould it be possible to make with only some LEDs, a few resistors and some pin headers to connect the ribbon cables to? and some buttons or switches to activate it?I saw this too but it looks a lot more complicated.https://www.gadgetronicx.com/idc-ribbon-cable-tester-circuit/

author: Rerouter
author_rank: Super Contributor
timestamp: November 10, 2019, 08:16:33 am
content: If you just need to make sure no connections are open, then yes you can do it with passives,If you want to make sure there are no shorts / reversed connections, then you would need something like a decade counter and a 555 clock, so it gives each pin a positive in sequence,

author: AVGresponding
author_rank: Super Contributor
timestamp: November 10, 2019, 08:38:44 am
content: You don't need anything more than resistors, diodes, LEDs, and switches.Start by drawing out a truth table, that will help you design the diode/switch logic.Bear in mind, the higher the number of conductors, the more complicated your switches are going to need to be!

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 08:42:37 am
content: Or just put a push-button switch on each line and test each line manually.

author: Shock
author_rank: Super Contributor
timestamp: November 10, 2019, 08:42:53 am
content: Send data over 8 wires with a loop back connector using the other 8 wires.Edit:Or what about 2 wires looped back 7 times.

author: Mp3
author_rank: Frequent Contributor
timestamp: November 10, 2019, 08:49:54 am
content: Quote from: Shock on November 10, 2019, 08:42:53 amHow would one accomplish this? I feel like a 555 can handle this, but i'm not quite sure where to start.It seems like it could be very elegant.

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 08:52:06 am
content: Quote from: Shock on November 10, 2019, 08:42:53 amHow would that detect a short between two adjacent wires?

author: janoc
author_rank: Super Contributor
timestamp: November 10, 2019, 08:54:47 am
content: Quote from: soldar on November 10, 2019, 08:52:06 amOr wires crossed twice - the second swap would cancel out the first one and the cable would be still bad while you are none the wiser ... Probably not a likely problem with IDC connectors, but the OP didn't say what kind of faults they want to test for.

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 08:55:01 am
content: Quote from: Mp3 on November 10, 2019, 08:52:13 amWhere can I find "passive" ICs and microcontrollers? I never heard of them.

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 08:57:11 am
content: One switch per line. One actuator closes the even numbered switches, another actuator closes the odd numbered switches.

author: Muttley Snickers
author_rank: Unknown
timestamp: November 10, 2019, 08:58:36 am
content: I was thinking that perhaps a basic LAN Cable Tester would suffice to quickly check for opens, shorts and crossed lines between each connector. The only drawback is that you would need to conduct two tests on each ribbon cable as most of these testers are limited to only four pairs or eight wires.

author: Mp3
author_rank: Frequent Contributor
timestamp: November 10, 2019, 09:04:02 am
content: Quote from: Muttley Snickers on November 10, 2019, 08:58:36 amInteresting idea....!I could make a board which connects each end of the ribbon wire to some switches which would switch between the low 8 and high 8 pins on each 16 pin ribbon connector?It's a little less DIY than making the whole tester from scratch, but might be more reliable for finding shorts.

author: Rerouter
author_rank: Super Contributor
timestamp: November 10, 2019, 09:26:08 am
content: Or if you want to go back to micros e.g. a atmega328, have 2 shift registers to feed the pins on one side, and wire to the micro inputs on the other side, you can check for every possible short open or cross,First test shorts / crossed wires, enter a 1 to the shift register and clock it along, each clock the micro should see only the expected pin go highThen test poor connections, clear the shift register so it is low on all pins, turn on the pin pull ups for each micro input, and read them, if any are not low, then you have a poor connection.

author: Mp3
author_rank: Frequent Contributor
timestamp: November 10, 2019, 09:27:09 am
content: I think i have a slightly better grasp on this.I think i will base it on this:https://cdn.instructables.com/FYK/WOL6/JLMKK0XP/FYKWOL6JLMKK0XP.LARGE.jpgAnd then i guess all i need to do is figure out the best way to test all 16 conductors. Since this circuit is for an ethernet cable, it has no problem stopping at 9 conductors.I'm imagining i would need a ON-ON, SPDT switch to somehow switch between the top & bottom 8...

author: Rerouter
author_rank: Super Contributor
timestamp: November 10, 2019, 09:58:33 am
content: If you want to go the micro route, here is a schematic I just through together (MISO would act as the shift register latch, assuming your just going to bit-bang this)Edit: you would add something like 220 ohm resistors to each pin on 1 plug so a short doesn't overload the shift register

author: Mp3
author_rank: Frequent Contributor
timestamp: November 10, 2019, 10:11:16 am
content: Wow man.... thank you! that's amazing, though i barely understand itI will spend a while studying and get to understand what's going on!!Would that linking of two 74HC595 work in a non-micro based circuit as well? I assume it would. What if i just used one 74HC595 and used a 8-pole switch, or a SPDT ON-ON connected to an analog multiplexer IC to switch between the two sets of 8 conductors so i could use just one 74HC595?(I'm not against your design at all, just trying to understand the possibilities and how it works.)

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 03:32:07 pm
content: I cannot think of anything simpler than this:

author: Yansi
author_rank: Super Contributor
timestamp: November 10, 2019, 04:00:34 pm
content: Quote from: Rerouter on November 10, 2019, 09:58:33 amWhat do you need the crystal for and where is all the decoupling?

author: Rerouter
author_rank: Super Contributor
timestamp: November 10, 2019, 08:03:00 pm
content: You likely do not need the crystal, that was just so it would work with the usual arduino bootloader, e.g. pop the chip off an UNO board and pop it in his circuit. This was an assumption to make it more available to beginnersDecoupling like the output resistors for the shift registers got missed because I literally threw it together in a few minutes.

author: janoc
author_rank: Super Contributor
timestamp: November 10, 2019, 10:33:17 pm
content: Quote from: soldar on November 10, 2019, 03:32:07 pmThat won't detect swapped wires (maybe not a bit problem with IDC connector) nor a short between adjacent wires.

author: soldar
author_rank: Super Contributor
timestamp: November 10, 2019, 11:02:50 pm
content: Quote from: janoc on November 10, 2019, 10:33:17 pmNot a problem with ribbon cables which is what we are discussing.Correction: Yes, it would as the wrong light would turn on.Quote from: janoc on November 10, 2019, 10:33:17 pmI believe you are mistaken. Think about it. One push-button switch tests the continuity of the even-numbered wires and the other one the odd numbered wires. If there is a short between adjacent wires then any switch would light both lights.Correction: You are right. The lights would need to go at the other end, connected to gnd. That would solve it.

author: Shock
author_rank: Super Contributor
timestamp: November 11, 2019, 01:53:18 am
content: I like the way you took my idea of the loopback and made the worst possible implementation of it by connecting adjacent traces.You can measure voltage drop with a mV meter to characterize the length and connection quality. But for simple signal integrity A PC can be used to test data over serial/parallel/ethernet loopback with existing software. I don't see a point in making a dumb tester that really tells you nothing about the cables performance.

author: hamster_nz
author_rank: Super Contributor
timestamp: November 11, 2019, 03:24:35 am
content: Rather than an switch for each wire, just use three buttons?First buttons test wires 1,4,7,10...Second buttons tests wires 2,5,8,11,....Third buttons tests wires 3,6,9...It would pick up any open wires, shorts to a neighbor, and shorts to neighbor's neighbor.It could also pick up a backwards error, as the LED 1, 2 & 3 will not light in the same order as the buttons are pushed.You could most likely get away with two buttons to test odd and even wires, but having seen the inside of an IDC connector I think that a short between might be possible with a bent 'barb' that pierces the cable (or whatever they are called).EDIT: A link to another thread on the topichttps://www.eevblog.com/forum/projects/ribbon-cable-idc-connector-failure-modes/

author: soldar
author_rank: Super Contributor
timestamp: November 11, 2019, 06:54:24 am
content: Quote from: Shock on November 11, 2019, 01:53:18 amAre you talking to me? And, if so, can you explain what is wrong with my idea? You know, rather than just saying it is the worst.

author: Moshly
author_rank: Regular Contributor
timestamp: November 11, 2019, 07:30:19 am
content: You could use a multimeter and have a big series loop with a different value resistors at each node, & just measure the total resistance.

author: latigid on
author_rank: Contributor
timestamp: October 23, 2020, 10:55:29 pm
content: Solid-state cable tester?Pretty simple really, counters and drivers with good cables indicating a diagonal line. Bad cables have dark LEDs, LEDs lit off-axis (short circuit), offsets, or inverted from the other corners.https://www.midiphy.com/en/shop-details/177/84/midiphy-wirescanner-pcb-midiphy-wirescanner-idc-micromatch-ribbon-cable-diagnostics

author: cdev
author_rank: Super Contributor
timestamp: October 24, 2020, 03:10:46 am
content: Yes, if you also have some electricity, you can use passive LCD (thermal sensing) material.Cables with continuity will heat up, those without wont.Quote from: Mp3 on November 10, 2019, 08:08:37 am

author: vk6zgo
author_rank: Super Contributor
timestamp: October 24, 2020, 12:12:55 pm
content: Quote from: Moshly on November 11, 2019, 07:30:19 amBut, but, that isn't complex enough for this forum!

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 24, 2020, 12:19:00 pm
content: hi,simpliest, just send 5V voltage on some wire and at the other end do a global short, back on input side put leds+resistors. if by hazard the 5V wire is bad reverse the cable.simple is good.of course if you want testing the current capability, add on each wire some chargelike others are saying, with an arduino you can make a smarter test in 11-2 hours using the gpib's and some buffer transistors or scrapped uln/udn chip (it takes half an hour to make the sw and maybe a hour to solder the board between arduino and cable).I suggest you test continuity AND current capability on each track.I used to manufacture in one company a machine with 10-way ribbon cable, never had an issue with them (the testing was done after the ribbon was assembled inside and we tested the machine for minimum 8h, so it was no need to check the ribbon before). never had a ribbon deadand the machine was a laser alignement system for radio-therapy. the ribbon was of course chinese fab (ordered usually by 1000 pcs). I guess you're concerned with no reason or your app is military-one !?regards,pierre