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I wired up a latching hall effect sensor to an LED. My power source is a stack of three 1.5v coin cell batteries.

Sensor was working just last night and then all of a sudden I tried it again this morning it is not working.

The only thing that I’m thinking is maybe the batteries aren’t strong enough because the sensor I think requires a minimum voltage of 3.5 V?

Took the leads off and tested the battery and it was showing only 2.5V..

Reason why I am a little confused is because last night I tested it by hooking it up to a very small low power LED which couldn’t have pulled that much power out of the battery...

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  • \$\begingroup\$ What is your actual question? Are you asking us to guess if your unspecified sensor will work at 2.5 V? \$\endgroup\$
    – Transistor
    Commented Feb 23, 2018 at 15:13
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    \$\begingroup\$ The LED may have been low power, but what resistor were you using to drive it? Use that information to figure out how much current was being drawn continuously, then check out the mAh of your coin cell batteries (which I can assure you is not a lot). Use maths to figure out if this was your problem, if not, reword the question into something that actually asks something \$\endgroup\$
    – MCG
    Commented Feb 23, 2018 at 15:15
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    \$\begingroup\$ Specifically, this is an ATS177 single output Hall effect latch from Diodes Incorporated. I’m not familiar with these sensors and have only been using mechanical switches in the past that don’t require a minimum operating voltage. My question is: do these sensors have to have 3.5 V input at all times? Or will it stop working if the voltage drops at all due to low capacity of coin cell batteries? Hope this helps clarify things \$\endgroup\$
    – Vbs
    Commented Feb 23, 2018 at 15:17
  • \$\begingroup\$ Hall effect sensors use a current to detect magnetic fields, this current will pose an additional load on your tiny batteries, for the ATS177 this means 5 to 10 mA drain on the battery even while the output is off. if you need magnetic activation, look into using a reed switch instead. \$\endgroup\$
    – Jasen Слава Україні
    Commented Feb 24, 2018 at 0:14
  • \$\begingroup\$ Yes I am aware of the reed switch, just need a way to somehow tweak it so it’s “latching”. Any way to do that? \$\endgroup\$
    – Vbs
    Commented Feb 24, 2018 at 15:02

2 Answers 2

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The sensor: ATS177

The front page of the data sheet: -

enter image description here

My question is: do these sensors have to have 3.5 V input at all times? Or will it stop working if the voltage drops at all due to low capacity of coin cell batteries?

See the red box above.

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Hall effect sensors use a current to detect magnetic fields, This current will pose an additional load on your tiny batteries.

For the ATS177 this means 5 to 10 mA drain on the battery even while the output is off.

If you need magnetic activation, you can use a reed switch instead. a magnet can be fixed near it to cause it to be stable in both the off and on positions.

To this up do take the switch and a magnet. move the magnet towards the switch until it turns on, then mark that place, then move it away until it turns off and mark that place, then glue it in the half-way position. after that a second magnet can be used to flip the switch between on and off.

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  • \$\begingroup\$ Thank you this was very helpful! Yes I need magnetic activation. Can you please explain how the magnet can make the reed switch stable in the on/off position? Really appreciate this feedback as I didn’t know that the other sensor put that constant drain on the battery. \$\endgroup\$
    – Vbs
    Commented Feb 24, 2018 at 13:33

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