Thread: Tutorial - Voltage divider - Measuring Voltages greater than 5vDC

got it! I guess I missed that part but that makes sense. thanks

yeah, and the reason for the optoisolator is that if something ever goes wrong, there's no electrical path between the high voltage and the brain

Thanks for the write-up! I've learned from this, but would I use this same method to read voltage between -12VDC to 0VDC? I read voltages less than -5VDC will damage the brain. For instance, reading a single-wire sending unit that passes common ground.

-Darkwind

-12 volts? what application do you have for this?

My good old Berlinetta. All of my inputs are passing either switched Ground, except for the temp sensors and a photosensor.

I would like to read a switched Ground momentary. Would I be better off using relays to convert Ground to +12VDC the use a voltage divider to bring her down to +5VDC to read the input?

As far as the other inputs, some are single wire sending units that are self-grounding and the others are two wire that input a ground and output the signal. The gauges will read resistance in Ohms, will I need to do anything to prevent hurting the FB? That's all I'm worried about.

Thanks.
-Darkwind


EDITED: I really would like to put mind on paper correctly, as to not seem stupid when typing

-12v? are you sure you have the multimeter probes connected to the right wires? seems like you may have the negative connected where the positive should be and vice versa..

I could be wrong though....

Negative... The Camaro Berlinetta has fingertip controls that pass either constant or momentary ground when pressed, it is the way it was designed. The signal then passes through a relay center, then to the accessories controlled by the switch (except ign,windows,doors,hatch they all pass normally.) This is different than standard Camaros that have pull-type headlight switches, and other switches such as interior lights,wipers, and anything else +12VDC switched.

Hope this clears some stuff up for everyone. At first I thought something was wrong on my end until i obtained an Alldata wiring schematic.

-Darkwind

EDITED: I don't know how to write...

I personally have never heard of negative voltage. usually when a multimeter reads in negative voltages, its because the probes are in the wrong polarity. what happens when you switch the probes? does it turn into positive? isnt that what you are looking for?

And this is where my mind doesn't work with my typing. The switches pass chassis ground to control relays.

I was re-reading what I wrote and realized where I made zero sense. Ahh... proof reading.
::Facepalm::

-Darkwind