- Mon Jan 21, 2019 4:21 pm
#80197
Hello, I have an application where I have a discrete sensor connected to the esp8266's gpio through a bipolar transistor so that when the transistor is turned it pulls the pin down, resulting in a low reading. but after triggering the sensor must remain low for a few moments after the event that triggers it, so I chose to use a capacitor connected from the gpio to the ground so that when the capacitor is turned on it quickly discharges and takes time to charge keeping low level at a time. my doubt: this capacitor load would come from the internal pullup resistor of the gpio configured for input pull up and I'm not sure if that is possible or safe. can I use the gpio in pull up to charge the capacitor or should I use an external pull up and disable the internal?
- Mon Jan 21, 2019 6:15 pm
#80199
Nothing wrong with this. You won't damage anything. Just make sure you have enough of an allowance for variations in the charge current. The pull up resistance is not specified as a particular value, and I am not sure what kind of variation there can be in normal use.
- Mon Jan 21, 2019 9:46 pm
#80201
thank you, the value of the pull up resistor will tell the wait time and this does not need to be very accurate
