resistor for 3.3V pull-up/down on LilyGO TTGO T-Call ESP32 - with SIM800L

Hello

I made a circuit with arduino and A6 GPRS module sending an sms when the connection between two wires is broken (trigger, with 100K pull-down resistor). This works fine.

To make things smaller, I am trying to build a similar project with the Lilygo TTGO T-call ESP32 SIM 800L

I read “The pins on the board are directly connected to the ESP32 chip and are therefore only suitable for 3.3V signals.”

If I am making a trigger with a wire between 3.3V and a GPIO and the ground, what should be the value of the resistor ?

(U=RI … 3.3V=RI … but where do I find the maximum current) ?

Regards
Diederik

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There is a mathematical formula called Ohm’s law, that will allow you to calculate the maximum current. There is an old rule of thumb that you need at least 1mA current to keep contacts clean. Again Ohm’s law comes into use. As far as maximum current if it is the resistor calculate it. If it is for the ESP32 pin read the data sheet. Here is a link to the calculator.
https://www.rapidtables.com/calc/electric/ohms-law-calculator.html

Yes, but to calculate it, I do need the maximum allowed current, and I don’t find the value. Maybe I am just looking for the wrong thing, but I don’t find anything like ‘maximum current’ on a datasheet of the esp32.

As far as maximum current if it is the resistor calculate it. If it is for the ESP32 pin read the data sheet

From what you write, I do understand there is a difference between the esp 32 pin and other pins?

Regards
Diederik

Diederik,

Did you get an answer to your resistor question?

I am using 10K as pulldown resistors in my project.

Although currently when the SIM connects to the provider, sometimes I have issues, I´m wondering if this is due to the resistor and the SIM chip.

I just wondered if you solved your question.

Regards,
grichfitz