1.1 IoT design w/ capacitive probe
1.2 Visual control w/ capacitive probe
1.3 Visual control w/ resistive probe
2. Soil moisture sensors
Either one of the following sensor types can be used for the moisture measurement (sensor output here connected to ADC0/GP26):
- Capacitive type sensor HW-390 (also referred to as v2.0)
- Resistive type sensor ME110
An initialization routine identifies the connected sensor type (see MicroPython code in my github repo). The capacitive probe should be preferred though since that is the durable sensor that won't corrode.
3. Humidity sensor
Prototypes are also utilized for relative humidity measurements with HIH 4020 sensor (see photos). Algorithm has to be modified for this as a matter of course.
A very basic output in a web browser can look like this:
At present I am using three different variants of common cathode 7-Segment-Displays which are pretty much interchangeable:
- SC56-11GWA: green
- SC56-11EWA: red
- SC56-11YWA: yellow (those I personally like the most)
Red LEDs usually have the lowest threshold voltage, green LEDS the highest (keeping in mind the statistical dispersion with LEDs).
Driving the segments (i. e. LEDs) of the 7-Segment-Displays directly is probably not good an idea since one individual Pico GPIO can deliver 12 mA at most, and it is unclear what the Pico's supply current upper limit is (on all its GPIOs combined). The documentation states something about 50mA, what is clearly not enough to drive a lot of segments at once.
The CD4511BE driver has a V_BE voltage drop (see data sheet), and so have the multiplexing transistors. That leads to a diminished voltage budget for the segment LEDs and the resistors R1-R7, respectively, what must be taken into account when calculating the resistor values.