Case for Pi Pico power/SWR meter
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Case for Pi Pico power/SWR meter using Kits-n-Partrs sampling bridge and a 20x4 display.
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Case for Pi Pico power/SWR meter using Kits-n-Parts sampling bridge and a 20x4 display. Be careful to select a 3.3 volt display.
The Pico 2 ADC is used to sample the bridge forward and reverse voltages. The MicroPython code on the Pico calibrates the voltages and displays average and peak forward and reverse RF power as well as SWR.
The PIco also reports quantities out through the USB for capture and analysis. The Pico can sample as fast as every 1 ms with display disabled.
Code is here: https://github.com/rkayakr/Pico-SWR
I wound my sampling toroid's with 16 turns to lower the voltage to less than 3.3 volts for the Pico ADC for inputs up to 50 watts. Adjust the bridge pots to less than 3.3 volts before putting the bridge in the case. I calibrated mine using an oscilloscope to neasure the RF voltage and then did a 2nd order polynomial to fit to the measured power vs sampled voltage plot which had a excellent fit coeff of .999.
The case is designed for 3 mm and 2 mm self tapping screws. You will also need 2 10 kohm resisters to shunt the sampled voltages to ground. A post is provided to mount a ring terminal for attachment of ground wires and resisters. I used the PICO ADC ground AGND GP27 for the bridge and a different ground pin for the LCD.