I am new here and have just started playing with the Arduino.
I do a lot of work with serial data and checking the voltage levels of the data and wanted to create a project that could do both with one set of probes, so i was wondering about the best way of switching between the different signals.
i have thrown together a quick drawing of my thoughts using relays (attached), but would prefer a way of doing it with a semiconductor device, i realise i have not added the potential divider to the circuit and a lot of other stuff, it was just me thinking of a way to use the digital outputs (two of them), to switch the input.
could someone point me in the best direction, and where i should be researching?
The voltage is generally between 0 and 30 volts DC, i was going to used a divider for up to 55v for buffer.
the serial data will be 422/232 so i will incorporate opto isolation and conversion to TTL.
I have done some searches and found ADG5436F, but not sure if this it the best way to go, or even if it is the right thing to use.
Well you certainly can't drive a relay coils direct from logic signals off the Arduino, that will burn out the
chip.
Relay coils need a transistor to amplify the current and a free-wheel diode to prevent inductive
kick-back.
However there's little point switching between different Arduino pins, you can connect to both an
analog pin and a serial pin at the same time. So long as you don't make both OUTPUTs at the same
time no problem.
What i am looking to do is have the device check a voltage between 0 and 34v
I did look at the potential divider but worried if the voltage went above 55v ( i would use 100k and 10k for the divider to give some head room).
I have looked at adding a 39v zener to the input along with 1375ohm 5W resistors (500, 500, 300 and 75 ohm in series) so if the input voltage is above 39 then then zener should kick in and the 5W resistors should take the brunt??? (protection.png)
Not sure if i have this correct, most of the articles i have seen have the zener (5.1v) on the input pin of the arduino, but there are problems as the voltage gets close the the 5v maximum of the pin, i wasn't sure if it would be better to have the zener at the input prior to the potential divider??
Another thought i has was what happens if the signal is reversed, thus the 30v is put on the 0v line, so i thought about adding a PFET so stop this (protection1.png)
Not sure if i have this worked out right or not, before i connect anything to my arduino i will be thoroughly testing any circuit on its own with a variable power supply, before conneting.
