Hi, I am freshman in electronics design. Recently, I was troubled by the power and signal design in PCB board. I hope someone can help me, thank you. I have two PCB board, PCB A and PCB B. There is information exchanging these two PCB ,but PCB A and PCB are powered by separated power(5V DC power). At first, I just connect the signal wires between PCB A and PCB B, then I find both PCB A and PCB B can't work well. Then I realize that the Ground of these two PCB board should be connected together. After that, these PCB boards begin working, but they get wrong data frequently. At last, I make these two PCB powered by one power, then they work well.
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My question:
How the power and signal wires design between tow PCB board which powered by
separated power.
Thank you.
and signal design in PCB board. I hope someone can help me, thank you.
two PCB ,but PCB A and PCB are powered by separated power(5V DC power).
both PCB A and PCB B can't work well.
together. After that, these PCB boards begin working, but they get wrong data frequently.
separated power.
May I suggest one of your supplies is noisy? Also, you could be getting what they call a ground loop.. Some times you need a signal isolator.
There are other problems to consider.. on some inputs of devices, The signal may get clipped, compressed or modified in shape a little. This modification may effect the other device that is listening to the signal.
I don't know what kind of signal you are working with however, I usually try to make sure this does not happen by using a resistor on the input and hope that does not cause more problems.
THe best solution is to have a unity gain stage on the device as a buffer, if it looks apparent in any way that the signal could get unintentionally modified.
If you put a scope on the signal you may see it drop in level, this maybe due to insufficient signal drive or, one of the devices has a over voltage clamp near by.
A perfect example I can share is a Zumbach Laser monitor system where I monitored a encoder pulse. The problem here is, it has internal clamps that won't allow the signal to reach past 7 volts on the input. That is fine however, if other devices are also connected to this same encoder reference, they may need 10V volts or more. Putting a R in series will relieve the compressed load so that other devices will see 10 Volts however, the Zumbach now has to much capacitance on the input for high speed pulses. Either way you can't win. The fix for that was, a unity gain amp to the device compressing the signal. Or, just a high speed signal isolator.
You really need to get a scope on the signals and see what is there.
and signal design in PCB board. I hope someone can help me, thank you.
two PCB ,but PCB A and PCB are powered by separated power(5V DC power).
both PCB A and PCB B can't work well.
together. After that, these PCB boards begin working, but they get wrong data frequently.
Hello,
you should look for another problem too. If one of the power supplies fail, the gates on the board with no supply which receive signals from the other board may be destroyed. Look in the datasheets if the input may get a higher voltage than the power pin.
You may have too few ground connections between the boards and not enough distributed decoupling capacitors on both boards.
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