Electronic – How to create a circuit for this signal? Transistor

esp32transistors

today I measured a signal with my oszilloscope. Its a pressed button of my robotic vacuum cleaner. The strange thing for me is, that in idle mode (button not pressed) the signal level is at 3.3 volts. But if I press the button the voltage goes up to 4.5 volts and drops than to 800 mV. This repeats until I release the button.

Its a SPST button like you find on a keypad.

The button starts the robot. I don't want to press it every time manually, I want to "press" the button remote via the GPIOs of my ESP.

I measured the voltage on the mainboard. There is a pin header where the button is connected directly to the mainboard.

What I want to do is now, I want to trigger the button via the GPIO of my ESP32. Do you have clue what kind of transistor-circuit I need? I need to raise the current somehow to 4.5 volts…

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Thanks

Best Answer

You haven't told us much about the nature of the button (number of poles, number of throws), but if a Single Pole, Double Throw (SPDT) button is being used, here's one way you could get that effect.

schematic

simulate this circuit – Schematic created using CircuitLab

But it sounds like you are trying to replace that effective circuit with an equivalent implementation that listens to the button state and outputs either 3.3V or a 250Hz 0-4.5V square wave.

One way to get that effect would be to use an 2-to-1 analog multiplexer, plugin 3.3V into one of its inputs, and plug in the output of a circuit that generates the square 0-4.5V square wave constantly, then use your ESP32 to set the control bits to the analog multiplexer to output the correct input channel based on the state of the button, which you are also tracking with the ESP32.

Assuming you have a 4.5V source voltage, the following circuit will convert a 0-3.3V square wave into a 0-4.5V square wave.

schematic

simulate this circuit

Obviously, this requires you to decouple the button from the current circuit and treat it as a "dumb" input to your microcontroller, then disconnect the node which generates the output you measured with your scope and instead connect that node to the output of the analog multiplexer.

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