what value resistor should be used as a pull down resistor with the moteino?
Depends how strong of a pull you need or what you're doing.
10K is a good general purpose value. Some special cases like i2c would ask for 4.7K (there's a little science behind that). So one value doesn't fit all, the same way a fixed size shoe doesn't fit every foot.
Im using it on an input pin connected to an esp8266.
In general in a pull down scenario, where the objective is to prevent the pin from picking up random electricity and going high, Is the main point of the resistor to prevent shorting to ground? So there isn't a maximum value just a min value to prevent the short?
Thanks
It's just ohms law. The stronger "pressure" wins. Pressure is voltage. You pull that line low. But if there is 5V on it and enough current (a few mA from a MCU pin), it will appear "high" (well it will divide and dip a little since some current will sink to GND through the resistor).
But I think you're on the good path :)
You are pulling the line to avoid noise or something else to pull that line up and cause a false HIGH. The lower the resistor the higher the current that sinks to GND and closer you get to shorting. You certainly don't want a HIGH signal to short to GND. In that case all the voltage meets no resistance to GND and all the current is sunken into GND, causing a short and probably bad things happen in the MCU that can't keep up with the current demand - effectively things heat up and eventually burn or fry your output, depending on how well protected it is in the MCU.
Makes sense?
makes sense.
i meant output on the moteino.
i put a 20k resistor and im still getting false highs.
i get it every 64 min
Pulling it down seems to have worked at night but during the day im getting the highs. sounds very weird.
any ideas?
thanks
It means your HIGH is caused by that pin going HIGH. It's an OUTPUT after all, so you have to check what is causing it to go HIGH.