EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: challie2 on May 01, 2018, 08:11:00 am
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Good Morning,
Could someone help me with a build.
Looking to build a multichannel selector circuit board.
The concept is that I want to be able to have 9 channels, that can be individually selected with a toggle push button, I want to be able to test RJ45 cables on a Multimeter to record impedance, it is for no project in particular but the engineering council I adhere to have standards in place that require me to do so.
I need it to provide impedance recordings as such cores 1-1, 2-2, 3-3, 4-4 and so on, we do not tend to use crossovers.
Unfortunately I cannot use an RJ45 banana plug as this shows the lowest impedance across all cores 9 there could be a break or a high impedance that would be hidden in this test additionally I do have a PC cable tester, but this only shows a Red LED lamp for the pinouts and does not provide a ohm reading.
Would appreciate any help perhaps there is even a multi meter adapter that will provide the facility of showing each of the cable individually?
Kind Regards
Jamie Newman
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If you want to connect to a multimeter and take readings manually, I would be inclined to use a mechanical rotary switch. The contacts might degrade over time and add some resistance, but assuming that this device sees occasional use, probably not a major problem in practice. Alternatively, you could use an analog multiplexer, either controlled by an up/down counter or a small microcontroller.
If you are only concerned about broken connections and can ignore the risk of shorts between adjacent wires, you would need a selector on one end of the cable only, and could connect all pins in parallel on the other end.
(If, on the other hand, you do need to look for shorts, that would stronly suggest a microcontroller to control the device. Stepping through all the "wrong" terminals for each position of the main selector would get annoying really quickly with fully manual control. In that case, the microcontroller would have to do the resistance reading as well -- at least a coarse one to check for shorts.)
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If you only need rough, uncalibrated measurements, you could consider using a system like this: https://hackaday.com/2011/07/24/using-an-arduino-to-measure-inductance/
to automate the measurements with a microcontroller.