Description
Attempting to build a device using the Arduino that will allow me to remotely restart a cluster of desktop computers that I have. The device works by momentarily connecting the RESET button jumpers on a desktop's motherboard. Two multiplexers are used so that 8 desktops can be connected to it at once. One multiplexer controls the reset button ground and the other controls the reset button positive terminal. Two multiplexers are needed to connect the same mother board ground to the same mother board positive.
Problem
The problem I am having is that the device works when connected to my laptop USB, but restarts the computer when I disconnect power. The device does not work at all when I connect it to the USB of my lunux server, instead seeming to send some kind of very weak signal to the mother board RESET leads that causes the mother board to freeze rather than reset.
I think the problem has to do with my limited understanding of the nuances of electrical flow through these devices. I feel like there must be some kind of backflow or small leakage that is causing disruptions for this use case. As you can see, I've added diodes connecting the power. This significantly lessens the chance of the motherboard restarting when I disconnect the power, but it still happens sometimes. Also, the device still only works when connected to my laptop USB and not my linux server USB. I feel like there is perhaps some configuration of diodes, capacitors or different types of switches that should be used. Such as a relay or MOSFET instead of the multiplexers?
I did try completely disconnecting the yellow wire before disconnecting the power, but this did not help. It seems that a signal is leaking from the mother board ground to the mother board positive through some other channel. The only thing that works is to physically disconnect one of the mother board leads from the board before disconnecting power. Connecting the mother board positive or ground to the arduino's positive or ground also does not reset the mother board. This implies to me that a signal is somehow leaking directly from one mother board lead to the other through the system.
Example
In the example below, only one desktop motherboard is connected for testing purposes (via the yellow and blue wires). The LEDs on the right side are for "debugging" purposes so I can see which control leads are actually delivering charge to the multiplexers. The green wires connect like control leads to each multiplexer (so A,B,C, and INHIBIT are the same for each one) and the yellow wire connecting the two multiplexers connects the "OUT" of the ground multiplexer to the "IN" of the positive jumper wire multiplexer.
Best Answer
I may be misunderstanding what you've done but it sounds like you're trying to use the multiplexers as if they are physically like this inside:
But, in fact, they're more like this inside:
The point being that the multiplexer is not actually connecting a particular input directly to the output, like a physical switch would do, but rather, a buffered version.
If you want to physically connect the reset switch positive pin to the motherboard ground, you can do that with, for example, an opto-isolator for each motherboard: