Seeing odd values on sensor UART

[kieran]

I'm getting really bizarre readings from the UART...

I've tried 2 different ESP8266s (d1 mini clones) and an ESP32 (a mini32) and see the same behaviour on each. The IKEA unit appears to work normally, and the LEDs on it light up as you would expect in different atmospheres.

Have also de/re-soldered the wires a few times, powered the ESP via either 5V pin or USB. Same deal each time.

Code modifications (for logging):

bool isValidHeader() {
  Serial.printf("Expected header: %02X %02X %02X\n", 0x16, 0x11, 0x0B);
  Serial.printf("Received header: %02X %02X %02X\n", serialRxBuf[0], serialRxBuf[1], serialRxBuf[2]);
  bool headerValid = serialRxBuf[0] == 0x16 && serialRxBuf[1] == 0x11 && serialRxBuf[2] == 0x0B;
  // ...

void handleUart(particleSensorState_t& state) {
  // ...
  Serial.print("Receiving: ");
  while (sensorSerial.available()) {
    serialRxBuf[rxBufIdx] = sensorSerial.read();
    Serial.printf("%02X ", serialRxBuf[rxBufIdx]);
    rxBufIdx++;
  // ...

Serial output

Receiving: F7 Done.
Expected header: 16 11 0B
Received header: F7 00 00
Received message with invalid header.

Receiving: FF Done.
Expected header: 16 11 0B
Received header: FF 00 00
Received message with invalid header.

Receiving: 7F FB Done.
Expected header: 16 11 0B
Received header: 7F FB 00
Received message with invalid header.

Receiving: EB FF FF Done.
Expected header: 16 11 0B
Received header: EB FF FF
Received message with invalid header.

Receiving: F7 FF FF Done.
Expected header: 16 11 0B
Received header: F7 FF FF
Received message with invalid header. 

I'm somewhat new to C++ / Arduino, would appreciate any tips re: where to look next!