I am looking for a switch so I can turn a GSM module on and off by micro controller?

Thread Starter

dan1010

Joined Jul 13, 2017
10
I am looking for a switch that i can control from a micro controller (espruino, 3.3v) to turn a GSM module (GSM800L) on and off.

The GSM module runs on 5v and takes too much power (2A peak) for the controller so it needs its own battery. But I want it off normally and only occasionally I want to switch it on to send an sms with the microcontroller.

There must be a simple way to just connect and disconnect the phones battery. When connected the module automatically connects to the network so that is all I need. The best I can come up with is some MOSFET based solution like this:
https://www.sparkfun.com/products/11214

Am I overlooking something obvious?
Thanks!
 

JWHassler

Joined Sep 25, 2013
306
The module has a 'power-on' input(pin 59).: a pulse turns it on.
There must be some programmatic way to turn it off: it quotes 7uA current draw in the 'off' state, which is low, but way more than it would draw if the battery were disconnected
 

Thread Starter

dan1010

Joined Jul 13, 2017
10
The GSM module (SIM800L) has an AT command for power off, but when i try that it automatically restarts in about ten seconds. Also, I don't want it on for more than a minute a day or so, so fully off would be ideal I think. The boards only have a limited number of connections, nothing to power off I think.

AT+CPOWD=1

 

Thread Starter

dan1010

Joined Jul 13, 2017
10
But I am mostly interested in finding a good way to control power to any peripheral using the controller I/O and some kind of switch.. surely they are common, I am pretty new to this
 

BobTPH

Joined Jun 5, 2013
8,952
A MOSFET is preferred method.

You would want to connect the MOSFET source to +5V, the drain to Vcc. You would need another transistor to drive the gate since the micro cannot output 5V to turn the MOSFET off (unless it has a 5V tolerant open-collector output.)

Circuit would look like this:

upload_2017-7-29_14-40-20.png

Bob
 
A MOSFET is preferred method.

You would want to connect the MOSFET source to +5V, the drain to Vcc. You would need another transistor to drive the gate since the micro cannot output 5V to turn the MOSFET off (unless it has a 5V tolerant open-collector output.)

Circuit would look like this:

View attachment 131852

Bob
Better to use the mosfet on the low side, then you dont use 0.5mA permanently just to keep him switched off ! Read up about using mosfets on the high side, your gate wont be fully turned on... If you use him on the low side (to Gnd) you only supply a gate charge when you need him, just use a 10k resister from the gate to ground to remove the gate charge when you switch the mosfet off
 
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