Pin (internal) resistance

[Toppert]

Is there a difference ins resistance between Pin19 et Pin18 and if yes, how much? And maybe how to calculate?

I will explain myself. Reading the pin value of some circuit via on of those pins have a different result depending of the temperature put on the circuit (higher temperature increases the resistance and therefore the voltage if I'm not mistaken). So I was thinking there was a difference at the basis resistance of these 2 pins and would explain my result.

I have a pin as configured as DAC going back to a certain Pin (here Pin19 for example) as Input pin with a Pull_Down resistance and then reading the value. Maybe the way I'm reading the value is not correct? I just want to check if the circuit is running correctly.

[jmarcelino]

@toppert
Do you mean you are reading different values using the ADC?

If so I think there's some electrical noise involved, not just thermal.

[robert-hh]

@toppert The value of the internal resistors activated via pull_up or pull_down is not well defined. Espressif just specifies a drive/sink strength of ~75 µA.
If you need a well defined input impedance, set the input to high impedance and add the resistor of your choice.
In addition, look into Pycom's pin sheets of the modules, if the ports are used for a certain other purpose.

[Toppert]

@jmarcelino It's without ADC (maybe I need to do it with an ADC). It's just a pin defined as input like :

pin = Pin('P19', mode = Pin.IN, pull = Pin.PULL_DOWN)
pin.value()

which gives me a simple 0 or 1 (I guess 1 when the voltage is at least half of the 3v3?).

I will check what the ADC version gives me next week (I have no module with me unfortunately this week-end). It might give me the reading I want.

Also thanks Robert for your answer, I will have a look into the pin sheets of the module.