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Topic: resistor issue? or something else? (Read 752 times) previous topic - next topic

Hey all, yet another working on an aquarium controller here. I am having what appears to be a resistor issue in my project. I have several float switches that are set up to either activate a relay or deactivate a relay based on the position of the switch. I have coded them as a digital in offering either a high or low condition via if statements. the float switches are wired in a pull-up fashion with 100kohm resistors (1/4w, 1%). When one of the switches is reading low, it is activating the relay to low as prescribed, however when it is in the HIGH position it is causing the led on all 3 of my connected relays to glow dimly. My other float switch, acts normally in the high position where the relay is not active, however when in the low position (that causes the relay to energize, it seems to cause a voltage drop to my temperature sensors.

have I done something wrong? or should I maybe try a pulldown?

any ideas are greatly appreciated!


First, I wouldn't use more than 47k for pullup, and more likely 22k or 10k. If the switch ties pin to low, use a pullup. If it ties pin to ugh, use a pulldown. Only one or the other is needed.
Second, what is the circuit with the relays? It sounds like the circuit is not right somehow, but we'd need to see it drank out to understand what it could be.

Thanks for the quick reply. I did some experimenting and re-proved my circuit for the switches. I am happy to report that my issues have been fixed (at least when it comes to the temp sensor). (also thanks for your input on when to use a pull up or pull down, I think that is the best thing I have learned all week). The temp sensors now function under all conditions.

Here is my only gremlin, which I think is a resistor issue again, but I think it just means I need something in between. If I use a 10k resistor on the pullup, when activated, it activates all 3 connected relays for a split second, then goes to just the one that should be on. If I use a 100k resistor, the board hums for 3/4second, then turns on only the relay that should be on.

James C4S

Sounds like a schematic is in order.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

is there a website I can use to draw that?

James C4S


or you can draw it on paper and upload a picture
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com


should be pretty self explanatory. Arduino pin is set to input

James C4S

That is a pull-down (not a pull-up) and I don't see any relays in that schematic.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

thats just the schematic for the switch, relays are just digital pin (a separate one) to input along with +5 and gnd

switched to pull-up w/10k resistors. board acts funky when running on 7.5v power supply. When connected to both 7.5v and usb, it works like a champ. What kind of power should I be running into the controller? 12v?

Yup, appears power supply was one of my main issues! I am now powering from a 12v computer power supply and it is running like a champ on the 10k pull up. Sometimes when I think out loud I can figure stuff out :D but usually it requires the motivation of smart people such as yourselves :D

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