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Topic: Reed Switch, to power the Arduino, turn on and off. (Read 135 times) previous topic - next topic

EDsteve

Hi,

i am trying to do almost exactly the same thing. Instead of the Arduino i am using a Wemos D1 (ESP) which is powered from a 3,7V lithium battery (charged by a solar panel)

Problem:
After turning on with a magnet. The reed switch stays on. It doesn't turn OFF any more.

What i tried:
1. I already tried three different reed switches
2. Moved to another place to avoid magnetic interference
3. I had the reed switch between batter (+) and Wemos (5V)
4. I had the reed switch between battery (-) and Wemos (GND)

The behavior doesn't change. Sometimes the reed switch turns off when i flick it. But only sometimes.

These are the specs of my reed switches:
Total length: 44.7MM
Glass length: 14.2MM
Diameter: 2.3MM
Electric shock load: 10W
Maximum switching voltage: 100 VDC/VAC
Maximum switching current: 0.5A
Electric shock capacitor: 0.7PF
Operating temperature range: -60~ +155 degrees
Maximum humidity: 98% (max)
Maximum working frequency: 100HZ
Startup value: 10-15
Release value: 5
Contact resistance: 100m ohm


It drives me crazy. Any thoughts?


Cheers
ED

P.S.: When i use the reed switch without connected to the circuit. It works fine.

Paul__B

Interesting suggestion - try a 0.47 Ohm resistor in series with the reed switch,

EDsteve

Interesting suggestion - try a 0.47 Ohm resistor in series with the reed switch,
Thanks for your answer. With the resistor in series the reed switch works as it should. Unfortunately the Wemos doesn't get enough power to boot. Hmm. What does that tell me?

EDsteve

Oh. I just realized, that i used a 47 Ohm resistor instead of a 0.47 Ohm.  ::)

So everything between 1 and 10 Ohm makes the thing work as i planned to. I don't have anything smaller than 1 Ohm.
Thanks. That basically solved my problem. But i still think this is a work-around. Why is this happening in the first place?


Paul__B

It tells you that the reed switch is welding closed when the lithium battery is first connected to the discharged input capacitor on the WeMOS D1 which is apparently 100 µF - much the same consequence as shorting the same capacitor when it is charged.

Kind of "spot welding".

It appears that the reed switch is the wrong thing to use as a power switch - the one you cite is tiny, a much larger one (40+ mm glass length) would probably survive.  :smiley-roll:

Addendum: OK, so if it works with a 1 Ohm, it would be within the Maximum switching current you cite.

UKHeliBob

Please do not send me PMs asking for help.  Post in the forum then everyone will benefit from seeing the questions and answers.

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