Using an Arduino Pro mini to read 4, 0 - 5v outputs of a device on A0, A1, A2, A3
Everything works but wondering about the length of wire, how long is too long (20awg - 18 awg) and if there are any concerns for the inputs of the Arduino. (the cap in the drawing is 0.1uf)
I've read a lot on here about protecting the inputs of an arduino and a lot of responses seem to be application specific. I'm not too concerned about over voltage, unless someone decided to start crisscrossing wires on a pre-made harness, So not sure I need to add Zeners but there is a slim chance someone could feed 12v into the input.
Space is a premium on the board with the Arduino so want to keep components to a minimum.
Thanks, as usual everyone here has been very helpful.
Not possible, there is no ground connection between Device and Pro-mini
You need a ground connection. Without a ground, there is no way of connecting any protection devices
Because risks are context-specific. And as with all risk management, you determine the list of risks, then figure out what odds and impact of each risk are, decide what is needed to mitigate each, and then decide whether the cost of doing so is justified. All this is application-specific, so there's by definition no generic answer to your question.
I understand that, I guess I can address issues as they arise. Right now I am only doing bench testing so no issues with EMF and the like. Once I get it into real world applications I can see what issues come up - if any.
The drawing is only showing the one of the four 0-5v output to the Arduini Analog input. The full wiring does have a hot and ground between the 2, just not shown.
What is the target for this and how long will the wires be. What is the environment. Note that wire is a big antenna. For the simplest of protection add a resistor in series with the input with the cap between the resistor and port.
All I get is a few boxes, far from a complete drawing.
As @jim-p noted there is no reference (ground) connection to the source. You could use 01005 resistors, they take very little space. Personally I have problems with anything smaller then a 0402 resistor. You can do the same with a cap.
Which is a problem because if you don't show the grounding arrangement then it's not possible to say if it is likely to cause problems for you.
I suggest that each remote device be connected with its own twisted pair or screened cable. Twisted pair should be one ground and one signal wire. Strictly one device per pair. Similar with screened cable, centre wire signal, screen ground. Either way the grounded conductor must not connect to anything else other than the remote device.
If anything else is missing from your diagram please create a new, complete diagram and post it.
What is the output impedance of the device? If the device can output a few mA without the voltage sagging, I would put a pulldown resistor at the analog input pin, (2.2k or so). Lower impedance, less EMI pickup.
On IO1, P1 is common ground between both devices
P2 is +12v, also common between both devices.
The +12v feeds a DC/DC converter requiring no external parts but has the same footprint as the 7805BTG, +12v in to +5v regulated out. This also supplies +5 to a touch panel connected to the TX/RX of the Arduino. (The touch panel and Arduino are mounted together)
P5 through P8 are the 0-5v inputs connected to A0 thought A3 on the Arduino.
C1 through C5 are 0.1uf caps.
D1 is simply there incase hot and ground get swapped, not perfect but simple.
The wire harness is shielded but not twisted pairs.
In addition to what Jim said, 2 conductors anywhere are not the same thing if there is any kind of component between them, that applies to ground or any other part of the circuit. There is only one ground, if you doubt this go outside and look around.
So, in your circuit in reply #17 there is no ground connection to I01. Not sure why you put a diode there, but there's no need and, even if there is a good reason for it, the way round you have it means it won't conduct anyway.
Well, when I apply ground to pin 1 and +12v to Pin 2, everything works - so not sure what you mean.
I realize there is a V-drop across the diode, but this is in the +12v side, the Arduino still gets 5v from the DC/DC. The diode is there so if someone connects +12v to pin 1 and ground to pin 2, nothing happens because the diode is revered bias in that case.
It's a connector, when the connector is plugged in, pin 1 is grounded.
Anyways, my main question is, should I be using any other protections on the analog inputs?
