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Help to modify push button (reed switch) power circuit

arjfca

Sep 12, 2013
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I want to have a circuit that will be activated on / off using a magnet over a read switch. This switch to be use ito power the receiver and servo in a radio controlled sailboat.

The original design came from this site

This actual circuit do power on, but the power off is intermittent. The original circuit was using a NPN transitor, but I modify it to use an N-mosfet to reduce power usage from the battery.

Any suggestion on modification to be apply on parts values or redesigning the circuit. The Vbat is from a LeFePo battery at 6.6V. I'm using a 2.2K hooked to Pout to simulate a charge

Any suggestion appreciated

Martin.
P.S. 1-excuse my English, more fluent in French
P.S 2 I did study electronic, but it was more than 40 years ago. My knowledge is a bit rusted


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Harald Kapp

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The original circuit was using a NPN transitor, but I modify it to use an N-mosfet to reduce power usage from the battery.
The base current to the original NPN is limited by R6 and therefore is probably neglible compared to the current through the load (2.2 k in your case). Therefore a NPN can be used easily.

What is the type of NMOS you use? Are you aware that you need an NMOS with a very low Vth? Often called "logic level" MOSFET.
 

arjfca

Sep 12, 2013
4
Joined
Sep 12, 2013
Messages
4
The base current to the original NPN is limited by R6 and therefore is probably neglible compared to the current through the load (2.2 k in your case). Therefore a NPN can be used easily.

What is the type of NMOS you use? Are you aware that you need an NMOS with a very low Vth? Often called "logic level" MOSFET.

Hello Harald.
The N-Mosfet is 2N7000

No i was not aware about the logicg mosfet. I will look for that. Never worked with mosfet before.

Martin
 

Bluejets

Oct 5, 2014
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I want to have a circuit that will be activated on / off using a magnet over a read switch. This switch to be use ito power the receiver and servo in a radio controlled sailboat.
We used very similar arrangement on RC aircraft.
Operation was, magnet in .....(in a brass tube with a red cloth marker)....switch off.
That way one couldn't loose the magnet in flight and have it switching off.

Below is the circuit we used and the pcb layout.

Note:- in the schematic below, the hall effect I did not have a symbol for, hence replaced with an opto isolator symbol.
It is a hall effect, possibly one of the later model one gets on the Arduino modules these days would be better.
KY-003......either way it's a connection to the 3 terminals on the pcb.

Module operation indicator is of no concern i.e. power draw as one only plugs in the supply battery before flight/sail.
Just watch orintation of the connections on the module.
 

Attachments

  • RC Magnet Switch.jpg
    RC Magnet Switch.jpg
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  • Board Layout.jpg
    Board Layout.jpg
    80.1 KB · Views: 3
  • KY-003.jpg
    KY-003.jpg
    99.5 KB · Views: 3
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