BloodPressureWifi

Plan: Add a Wemos D1 mini to my Beurer blood pressure monitor to publish results via MQTT.

• Photos: https://photos.app.goo.gl/GeWPxujQbdsRS84m7
• Helpful tutorial reading I2C EEPROM: https://www.edusteinhorst.com/hacking-a-blood-pressure-monitor/
• Nothing usable on GitHub: https://github.com/topics/blood-pressure
• DIY blood pressure monitor
• Needed hardware:
  • USB Logic Analyzer 24M 8CH (ordered on 31.03.2019 for 5.25$): AliExpress https://sigrok.org/wiki/VKTECH_saleae_clone
  • Wemos D1 mini
• Logic Analyzer Software:
  • https://sigrok.org/wiki/PulseView
    • Install WinUSB driver with Zadig and then select driver fx2lafw in PulseView.
  • https://www.saleae.com
  • https://www.ikalogic.com/scanastudio/
• Analyze HEX: https://hexed.it
• Application notes on oscillation signal: 1 2
• Chips in my Beurer blood pressure monitor:
  • CS-20A pressure sensor: https://brmlab.cz/user/jenda/cs-20a
  • CMOS Serial EEPROM: S-93C66BD (web, pdf; pins: page 2, lower half)
    • 256-word × 16-bit
    • Soldered cables to pins and connected to logic analyzer: CS:yellow:D0, SK:orange:D1, DI:red:D2, DO:brown:D3, GND:black
    • SPI decoder settings, first three blocks
    • Can also use the Microwire decoder with a stacked protocol decoder for 93xx EEPROM with 8 bit address size and 16 bit word size, but for writes it complains with 'Not enough word bits'.
    • Data is only written to EEPROM once the device is turned off after measuring.
• Measured a couple of times to figure out what the data means. A memory slot is 4x 16 bit words of data:

Block 1: DI: 100 11xxxxxx = Write enable
Block 2: DI: 110... = Read address 0 -> DO: 0x101 = 5 (start of next free memory slot)
Block 3: Write address 5, bin: 0000100000000100, hex: 08 04, ints: 8 (month) 4 (?, constant)
Block 4: Write address 6, bin: 0000101000010101, hex: 0A 15, ints: 10 (hour) 21 (day)
Block 5: Write address 7, bin: 0111010100100000, hex: 75 20, ints: 117 (high BP - 20) 32 (minutes)
Block 6: Write address 8, bin: 0011110001010111, hex: 3C 57, ints: 60 (HR) 87 (low BP)
Block 7: Write address 0, bin: 0000001000000010, hex: 02 02, ints: 2 2 (number of occupied memory slots)
Block 8: DI: 100 00xxxxxx = Write disable

• Did not find working SPI slave example for ESP8266. Tried: Arduino SPI (ESP8266 SPI.h does not expose SPI registers SPSR SPDR), SPISlave_Test (did not receive anything, maybe SS inverted?). Not tried: ESP8266_Microwire_EEPROM.
• Power:
  • AS: #58 ESP8266 Sensor runs 17 days on a coin cell/transmits data
  • Wemos D1 mini draws ~0.3mA in deep sleep which is too much. Could switch to ESP32 (10uA?).
  • For now just power it by holding a push-button (connected to 5.5V from its 4xAA batteries) while turning the blood pressure monitor off (LED on once it has connected to MQTT (~4s) and LED off once published).