Controlling 12v Bell via MOSFET

Other Hardware Motors, Mechanics, Power and CNC
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Hi all,

I have a circuit similar to the attached pic. To describe this, I have a 12v/5a power source which is split between feeding the MOSFET and a fixed 5v regulator. The output of the 5v regulator feeds the Arduino and has a 1000uf capacitor. A digital output of the Arduino triggers the MOSFET which supplies power to the 12v bell.

What happens is sometimes it seems to get ‘stuck’. I am trying to make the bell ‘ding’ rather than ‘ring’ so am writing high, delay of 25, writing low. If I wish to ring the bell multiple times (max. 3) I delay 75 and then repeat. The code is written in such a way that it should be impossible for the bell to sound more than 3 times or for more than the combined time that 3 times should take. Infrequently (1 out of 10, sometimes more often, sometimes less) it seems to get ‘stuck’ after I set high and so the bell continues to ring indefinitely. At this point the only way to recover is to reset the Arduino. It does/has worked, but sometimes doesn’t.

Any idea why it would be doing this?

Thanks in advance!

IMG_2449
IMG_24492480×3508 578 KB

2

You likely need to add a kick back diode to the bell.

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How you set high? Without code hard to answer...

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5v from the buck converter should go to the Arduino 5v pin (not the Arduino Vin pin).

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I second @Railroader recommendation and there is no need for that gigantic capacitor, it does nothing.

1 Like
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Looking at this example your bell wiring may be reversed
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Thanks all for the responses. I should have clarified the diagram is a approximate representation, the mosfet is wired the correct way but shown incorrect in the diagram.

@Railroader @jim-p I will try a kickback diode. Any advice on diode selection? I’m have a bunch of 1N4001s kicking around. And just to check this is a diode ‘reversed’ (diode + to bell -, diode - to bell +) in parallel with the bell itself?

Thanks again everyone

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Would likely work but personally I would use a 1N4007 if I had it.

Yes. Think like this: The current through the coil flowas from positive to negative. When the relay/transistor brakes the flow the diode should carry the current through the coil in the same direction.
Diodes had anodes amd kathodes, not + or -.

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Why.
The 1N4001 is better suited for low voltage.
And the diode will never see a higher reverse voltage than the supply.

I never understood why people prefer the 1N4007 for low voltage applications.
Vf is a bit higher and the 4005-4007 group is a bit slower than the 4001-4003 group.
Bigger is better doesn't work here. Not that it makes a difference in OP's application.
Leo..

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You're surely right. My mind was on the max current. Gotten a bit rusty here.

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@Railroader @Wawa thanks both for the help, I just run through 40 cycles without an issue. I used a 1N4001 in the end and seems to be working fine

1 Like
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Thanks for telling. Nice to know.

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