One single button to wake up a WeMos D1 and put it to sleep

Question

I am hoping to use a WeMos D1 Mini to control a Raspberry Pi. To save battery, I want to put the microcontroller into deep sleep and wake it up by pressing a button. The same button should be used to activate a method that will put the controller into deep sleep after shutting down the Raspberry Pi.

The thing is that the WeMos wakes up by shortly shorting the RST pin with GND. No problem with a push button. But when the microcontroller is awake, I don't want it to reset if the button is pressed - I rather want to detect the button press. So I am hoping to use two transistors, one NPN and another PNP, so that when I am waiting to wake up, the NPN allows the RST to connect to the button, where the other end is connected to ground via another NPN transistor enabled by the same base signal. When I want to detect a button press, the PNP will then allow the flow between the pins used for button reading.

So all transistors are using the same controller.

Except that it's not working. Last time my WeMos was even getting a bit hot, so I think I am shorting something.

Do I need diodes, for example between the button and the collectors of the two first transistors? Is there a better way to achieve this? (colours mean the wires do not touch)., f

Answer 1

At the very least, you're missing some parts. A transistor inverter needs a pull-up resistor on the collector (or a pull-down if it's a PNP), at the very least you're missing those. And it's difficult to do this sort of job with transistors in a way that is truly low power.

The way I'd do this is with an OR gate. If you can deal with surface-mount parts, use a 1-gate chip, otherwise use the lowest-power 74xx32 that fits your voltage level (74HC32 if 5V).

• The "RESET" signal goes to your WeMos's reset line.
• The "keep_on" line comes from your WeMos - I'm assuming that the WeMos chip will let this pin float when it's in reset. If it has an internal pull-up when it's reset, say so and we'll change the circuit. You'll need to configure this as an output, and set it to high, when you power on, and accept that you'll use some current in the resistor when its on.
• The "button_pressed" line goes back to some input on the WeMos. Again, I'm assuming that the WeMos will let this line float when in reset. If there's an internal pulldown in reset, then that'll cause problems.

^{simulate this circuit – Schematic created using CircuitLab}