I have an esp8266 with wifi on a NodeMCU board. The wifi is working fine.
I want to add a sim900 to the board, so that the wifi network configuration can be set by sending an SMS text message to the microcontroller.
I see that the sim900 can draw as much as 1A at 5 volts. Some websites even say 2 A.
There is a USB connector on the NodeMCU board, and it leads to a 3.3 volt regulator. Can I just solder a wire onto this regulator to get 5 volts to power the GSM? And if I do this, will I be able to power it from a laptop USB port, or would I need to use one of those high current USB chargers?
I'm thinking of using a power transistor (or a driver chip) so that one of the pins on the microcontroller can kill the power to the GSM. Can anyone suggest a suitable driver chip for this purpose?
USB can usually provide only around 500mA. Maybe USB 3+ can supply more, but that uses different connectors to those found on NodeMCU boards.
Even if it could supply more, you would not want all that current to pass through the NodeMCU board. Use a separate connector and take power wires from that to the NodeMCU and the GSM module separately, and use good quality wires.
I want my board to be versatile. If it's connected to a USB port somewhere (e.g. on the chair on a train), and the wifi connection is already configured and working, then I simply want to be able to use the wifi without ever powering the GSM 900.
But if the power source can push an amp or two at 5 volts then I want to be able to power the sim900.
What if I were to tag a wire directly from the USB port on the NodeMCU board, before it even reaches the voltage regulator? I'm talking right on the leg of the USB port. Then the current would only heat the USB port. Would that be ok, do you think?
Also can you suggest a driver chip I would use to toggle the power to the sim900?
It's possible that while the GSM board might draw high currents of 1-2A, this may only be for very short periods, like a few milliseconds or less. The average current can be much lower. If that is true, a large capacitor, across the power lines close to the GSM board, may be able to satisfy those short periods of high current, and the average current may be within the limits of the arduino board.
Do some measurements with a multimeter, with the GSM board performing different activities, to see what the average current is.