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Topic: Limit switch voltage too high for Arduino input (Read 579 times) previous topic - next topic


Jan 15, 2019, 05:39 am Last Edit: Jan 15, 2019, 05:40 am by denman
Okay, no jokes about having so many cheap meters or my ignorance in reading them!  LOL!

But... can you guys tell me which scale to read from on my other cheap meter (but not a clamp type)?  The dial is set on 0.5mA for both readings.  One picture is with the switch closed, but which scale do I get the reading from?  Is this 8mA * 0.5 = 4mA, or is it 40mA * 0.5 = 20mA.   At first I thought 4.  Now I'm thinking 20, but selection of the scale to read from has me confused and neither number is in line with what you guys had me expecting.  The door did stop when the switch closed even though the current was going through the meter.  I took a video, so if that would help let me know.  The 2nd picture is with the switch open (showing 0).  The 3rd picture is what I "think" you guys are saying to do with the circuit diagram.  Is this correct?


Jan 15, 2019, 06:35 am Last Edit: Jan 15, 2019, 07:45 am by outsider
DO NOT APPLY VOLTAGE TO THE METER ON A CURRENT RANGE, not even 0.1V! The fuse will blow!
You're on the 0.5 mA full scale setting, the needle is on 40 of a 50 scale, so 40 / 50 * 0.5 = 0.4 mA.
You have a wire from the input pin wire to ground, that's grounding out your signal, remove it.
When that is done, put your meter on the 50 DC volt scale first, put black lead to ground, red lead to input pin, if less than 10V, switch to 10V range, you should see about 5V when the switch is open and near 0 when switch closed.


Jan 15, 2019, 04:34 pm Last Edit: Jan 17, 2019, 06:31 pm by denman
Thanks @outsider.  Your caution is directed towards the right person that's for sure!   :smiley-yell:   For what it's worth, I at least knew that when checking current, the meter must be connected in series with the lead from the switch.  You should ask me how I know.  LOL

I had disconnected the lead between the GDO and the switch and then placed my meter in series between them.  That's more obvious in my video here.  But again, no jokes about my original mis-reading of the scale (or my redneck accent).  LOL!  https://drive.google.com/open?id=1myq3QAuzx0J7uN0C7Ywh8U2tMSwsYObX

I think I'm still confused some after your revision to my drawing.  Does this new drawing make sense?


Jan 15, 2019, 06:02 pm Last Edit: Jan 15, 2019, 06:03 pm by outsider
Like this.



Did you ever determine for sure what the voltage across the limit switch was? If it's only 5V you could get rid of the 4k7 resistor.


Jan 15, 2019, 09:01 pm Last Edit: Jan 15, 2019, 09:06 pm by denman
AH!!!  I get it now!  And...I had totally forgotten about that resistor!  Thanks for that picture modification.  Easy peezy.  Well...until I start soldering.   :smiley-yell:  

And to answer your last question...and I had remembered that you had warned me earlier in a previous post but wanted to double check for the polarity, yes, that is 7.7vdc + with respect to ground.  I went home at lunch to verify polarity.  I also connected it in reverse and when doing so it showed -7.7.  So I'm absolutely sure that the wire has +7.7 vdc and it grounds through the switch when it closes to signal to the motor to stop running.  Notice that I had disconnected the wire to check for voltage and the switch was in the closed position, so it doesn't stop the voltage feed when the switch closes or anything crazy like that.  It's +7.7vdc full time.

And please notice that there is a good use for amp clamps.....js



Jan 16, 2019, 07:00 pm Last Edit: Jan 17, 2019, 04:49 pm by denman
Thanks @outsider!

I have 2 limit switches, so which Arduino pin would I connect the 2nd one?

Also, will the signal from the rotary encoder connect directly to another Auduino pin without doing something similar?  Which Auduino pin for it?  Remember, that signal feed from the GDO has a constant voltage (see what I said below) but is labeled as a signal in the owners manual electrical diagram.

Next I checked the voltage on the terminals of the encoder.  The top wire (see picture attached) is a ground.  The middle reads 10.15v DC and the bottom terminal reads 4.15v DC when the motor is not running, but those readings drop some when the motor is running.

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