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2808 Voltage Drop

I am trying to use the #2808 Mini Pushbutton Power Switch to switch power to a Nodemcu dev board. I am using a 2XAA battery pack at around ~3V attached to the Vin of the power switch, and the Vout of the switch attached to the 3.3V pin of the NodeMCU. The Nodemcu has a basic program which boots up, connects to wifi, and sends a message via MQTT.

I notice that when the NodeMCU boots (when I press the power switch button), the voltage that it is getting from the switch drops to around 2V and it does not function. If I connect the batteries directly to the NodeMCU, it works fine, with the voltage around 3V. Does the #2808 really cause this much voltage drop? The NodeMCU typically uses about 80mA.

Hi.

I am sorry you are having trouble with your Mini Pushbutton Power Switch LV. I expect the voltage drop across the power switch to be negligible. When you see the issue, does the switch stay on? Could you post pictures that show how everything in your setup is connected? Could you try making sure your batteries are freshly charged or, if they are not rechargeable, try a new set? Could you look at the voltage at the input to your controller with an oscilloscope when it is turning on both directly from the battery and through the switch?

-Claire

Hello,

Thanks for the response. I have uploaded a pic of the setup below. I have actually switched to using a 3XAA setup, with the NodeMCU powered from the Vin pin rather than the 3.3V pin. I still get a voltage drop that keeps the NodeMCU from working. Here are my measured voltages:

With switch on, nothing connected to Vout:
Vout = 4.7V
Switch LED = ON

With switch on, Vout connected to NodeMCU (as pictured):
Vout = 3.7V
Switch LED = ON
NodeMCU’s 3.3V rail: 2.36V, NodeMCU does not operate

Battery directly connected to NodeMCU:
Vin = 4.35V
NodeMCU’s 3.3V rail: 3.3V, NodeMCU operates

Can you measure the voltage at various points in the circuit to make sure none of the wires or breadboard are causing the drop, and could you measure both the input and output of the switch in your second configuration (the one in your picture)? Are you sure you have the LV version of the power switch? If so, the power LED should be red.

Although the power switch does seem to be lowering the voltage much more than it should, from the voltage readings you gave, there is still a voltage drop when the battery is directly connected to the MCU too. I want to make sure there are not multiple issues in play here, so to rule out other problems, have you tried fresh batteries or any other type of battery or supply? How much current do you expect your NodeMCU to draw?

-Claire

It ended up being the breadboard that was bad. I swapped it out, and the voltage drop now appears to be minimal, what I would expect for the internal battery resistance; the switch seems to work fine. Gah!

Thanks for sticking it out with me on this.

Cheers,
Doofus

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