Blood Glucose Monitor Log

July 11th 2025

  • Boards arrive

  • Boards boot up

    • Able to establish communication with the RP2040

  • 5V analog rail only reaches 4.4V on all boards

    • Dropout of LDO is larger than expected

    • I tried increasing the boost output, but it the rail doesn’t reach the needed minimum 4.75V

    • For temporary fix, I will connect the rail directly to the USB VDD

      • This will introduce switch noise but there isn’t much that can be done about it

    • For long term fix, new LDO / boost needs to be sourced

      • Also add some way to gate the 5V rail to save power

July 15th 2025

  • Initial FW flashed an written to the boards

    • It was discovered that the PLL SPI interface is not connected correctly

    • SW based SPI can be used as temporary work around

July 23rd 2025

  • All components able to be communicated with except for USB PD

  • NFC does respond over I2C but we can’t read off NFC antenna

July 24th 2025

  • Realized USB PD has I2C pins swapped

    • Cut traces on one board to try to physically swapped the connections

    • Realized that this could be patched in SW by using a software defined I2C connection for the USB PD, and then swapping to I2C peripheral for the other components

  • Isues soldering balun
    • Pads are way to small to do by hand

      • Future revision pads should be made much wider to support handsoldering

      • Going to attempt to try solder paste

  • Measured resonator response on VNA

    • Used plastic bag filled with water and glucose to test different blood sugar levels

    • Measurable change in center frequency

  • Couldn’t get PLL to output

    • PLL says it is locking and outputing wave

    • Unclear if it is actually outputting, can’t be detected

July 25th 2025

  • Checked PLL out with AC multimeter

    • Reading only 0.15Vrms (-3.5dBm) output

  • Connected PLL to oscillisciope to measure 40Mhz output, nothing read

    • Issues with FW writing to PLL registers

    • Looked at SW defined SPI interface

    • Was able to interact with it and load registers

    • 600mVpp, 100kHz wave generate, PLL wasn’t locking

  • Attempted to use solder paste + heat gun to attach balun, succesful

    • Went back and redid other boards baluns

  • Was able to repair other board with the torn adjust resistor pad

    • Directly bridge resistor from +5V pad to pin

July 27th 2025

  • Was able to drive clean 70MHz sine wave output from PLL

    • 70MHz is max we could measure on scope

  • Issues with NFC, antenna doesn’t seem to be receiving anything

  • Issues with ADC, incorrect values

July 28th 2025

  • Confirmed NFC can recieve signals with a peak to peak voltage of over 3V

    • Investigating the packet format to see if its a phone issue

  • ADC is having issues reading the proper value

    • If it cannot be solved we will just attempt to read the output using a scope