GPIO Read interact with GND or VCC

[ULOK]

Hi,

I use STM32F103C8T6 a GPIO input pin to read a high or low signal from another GPIO output pin, and connect a 3Mohm resistor between two pins, and I notice touching GND with hand will influence the signal status, than I measure the resistance between GND and GPIO pin, it is around 10Mohm. I want to isolate the signal from GND interference, how should I do? I have to keep 3 Mohm resistor. will it be better if connect a capacitor between input pin and GND? or connect a large resistor in between?

[Andrew Neil]

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@ULOK wrote:

I have to keep 3 Mohm resistor. 

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Why??

At that level of resistance, it is to be expected that touching with a hand will be significant!

[ULOK]

Hi, it is intended for hand detection, but touching GND will also be detected which is surprise. 3Mohm vs. 10(or 6Mohm), I want to increase the resistance to GND so that GND will not influence signal that much.

[PGump.1 · Accepted solution]

Hi,

I would NOT recommend using GPIOs, directly, for that purpose.

In electronics, there are many Interface devices, for many purposes. I recommend finding one suitable for your application.

Many MCUs have integrated interfaces, perhaps there is a MCU with a suitable interface for your application...

I hope this helps.

Kind regards
Pedro

[ULOK]

Hi Pedro,

Can you recommend a MCU with such interface? and better have CAN interface too. STM32 series will be good to use. Thank you!

[Andrew Neil]

look at capacitive touch sensing - many microcontrollers have it built in, and there are also external chips available.