Hello. I am trying to set up a system to monitor voltage and current on the lines running to the sensor of an alarm system. I have got it to run on some set ups but am running into a problem with my attachment to the power line on one of my alarm setups.
I am putting a resistor in line with each of the four wires (+8v power, + sensor, and the two ground wires) , running them through a 4051 Multiplexer, and then amplifying the reading through an AD623 and then doing an analogRead on each wire then using Ohm's Law to get the current. Like I said, it works fine on some setups, but on one of them each time I read the + power wire it is alarming the system. I am currently using a 1 Ohm resistor which causes no problems being inline except when I do the read. I have tried a 0.1 Ohm resistor but it didn't make a difference.
I placed a high value resistor in front of the input into a multiplexer (10M Ohm) and it no longer alarmed, but I think that may have my readings too low to measure.
Honestly, I'm kind of unclear as to why the analogRead is even affecting this circuit. Is it perhaps too big a draw and is triggering the alarm?
Thanks for your help.
Code and schematic please.
I am currently using a 1 Ohm resistor which causes no problems being inline except when I do the read.
I'm guessing it's a ground problem. If the Arduino is grounded, but one side of the 1-Ohm resistor is not (normally) grounded, you are grounding something that shouldn't be grounded.
i.e. When you measure current with a multimeter the meter is usually "floating" (no ground connection).
Do you need an analog measurement for an alarm? Are you sure you need both voltage and current? What kind of sensors do you have that require an amplifier?
It's actually rare to even be concerned with current when we are talking about "signals" or data/status lines. Usually, we are just concerned with getting the right voltage (with some known-reasonable impedance/resistance).
Thanks fr the help so far.
I will get code and schematics up soon when I get home.
For my project I need to at least know if there is current on each wire or not. I would also find it very useful to determine in which direction the current is flowing.
I need to get these readings on different systems of 4 wires. Some will only have 3 wires with a common ground for the power and sensor wire. I need to know if the ground reading that I am getting is a return ground or just an unconnected wire. Like I said, direction of current flow on the wire would also be helpful.
I will have to research this floating reading business. Is there any way to do that on an arduino?
Thanks so much for the help so far.