How do I monitor/record signals on an FPC ribbon cable? - Page 1
Forum section: electronics / projects

author: cinna
author_rank: Newbie
timestamp: August 19, 2025, 06:06:02 am
content: Hi, I have not used this forum before, so I am sorry ahead of time if I am using it wrong.I have a camera where there are 6 FPC ribbon cables going into the "tape deck". How do I document the signals being sent to and from the tape deck, and how do I know which direction these signals are going? For example, are the signals coming from the circuit board, or is the tape deck communicating back to the board.Extra Info:- I can't probe them all individually with a multimeter as theres not enough space for me to fit the head of the probe into each small pin. It is also really difficult to keep track of, and I am not sure I am getting reliable data.- The reason I would like to capture the full log of this data is so I can see if there are transitions I need to know about as the tape deck changes the state it's in. Such as, tape deck is open -> tape is inserted -> tape deck is closed -> playback -> tape rewind -> etc.. I have probed some of this tediously, and have found the signals change depending on state (who could've guessed), but this hasn't helped much as I am not able to do it for the ones with more than 8 pins. It's too difficult to track which pin I'm on. It's like working on a modern car, it was made to be used, not worked on.- I have had my micrometer at 20V setting.- I have service manuals for the camera if anyone needs documentation to help, but I don't think it would be necessary.- I have a raspi (4+ B I think, and zero 2 w), dupont cables, and breakout boards (FPC connector to 2.54mm male for dupont cable) for all 6 FPC connectors if that can help me capture the data. I just don't know how to integrate this stuff with the tape deck connected. I need some sort of splitter involved essentially.Thanks, and let me know if you need more information. Down for all ideas, but I don't have a lot to spend on this. I am very inexperienced when it comes to this type of circuit work, so please assume I know less than you think!

author: Terry Bites
author_rank: Super Contributor
timestamp: August 23, 2025, 06:57:06 pm
content: You can get "FPC breakout boards" which you wire back to back giving you full access to all the lines.

author: MathWizard
author_rank: Super Contributor
timestamp: August 26, 2025, 12:19:06 am
content: Assuming its digital data, what you really want is a Logic Analyzer. And if it's a stereo or something, then 1 of the $20 8-channel USB LA's should be able to record most anything, and decode a lot of it too. I've worked out a bunch of stuff about 1 of my stereo's, using a LA. I can see data get sent by the buttons and remote, and I can see the commands get sent to various chips and circuits.It can be a pain to get the drivers and everything working for USB and, well for windows 10 anyways. But the PC software to use these $20 LA's is all freeware, and is easy enough to use. Pulseview is the name of the PC program.If you buy one on amazon, read the reviews and make sure most people aren't complaining about not being able to get it connected to windows. I'm not looking forward to the next time I format my whole PC, I'll have to find the drivers and everything all over again for all these little niche programs and tools.Then for hooking up to random circuits, I have a protoboard with 40, 2.5mm connectors, connected to 40 pieces of AWG28 wire, that I just tack onto the device under test. Then I just plug my LA's into that.Using Here's what it the startup of my stereo looks like, as seen from a MCU circuit I added, that listens to the commands sent to some volume and switch IC's, and converts it into 1 data stream. Some of the stereo's MCU is failing, and the volume IC's and others don't always get the commands. So I will have to start sending them myself.