OpenSprinkler › Forums › Hardware Questions › OpenSprinkler › Flow sensor routing on Open Sprinkler PCB itself? › Reply To: Flow sensor routing on Open Sprinkler PCB itself?
Eagle is free, you can download, install it, and open the circuit design files with it.
Dry contact sensors like rain sensor, reed switch flow sensor, can be directly connected between a GPIO pin and ground. These sensors are un-powered and behave just like switches. Most GPIO pins on ESP8266 (and I believe ESP32 as well) support internal pull-up so you don’t need external pull-up resistors. OpenSprinkler design also adds a 4.7K series resistors which is purely for protection purpose (in the past we’ve seen users carelessly plug in 24VAC into the sensor port, instantly toasting the microcontroller). If you can ensure such accidents won’t happen, there is no need to add the series resistor. If the sensor is placed outdoors, you may consider adding a MOV or TVS diode to protector the GPIO pin from surge voltages.