Skip to main content

dxTemp

1. Overview​

This module is part of the project dxmodules library. It provides HM infrared temperature measurement over UART: single-frame peak temperature (getTemp), multi-frame statistics (measure), full 32×32 thermal map (getThermalMap), and ROI / face-linked forehead temperature (getRectTemp), plus optional setCompensation calibration.

Main features include:

  • UART lifecycle: init / deinit for serial channel setup (dxUart underneath).
  • Multi-frame stats: measure(frames) — consecutive peak readings across full FOV (~125 ms between frames), returns max / min / avg and per-frame samples (compensation applied).
  • Simple temperature: getTemp() — single-frame peak over full 32×32 FOV.
  • Thermal map: getThermalMap() — raw grid + getPixel(col, row) helper.
  • Face ROI temperature: getRectTemp(rect) — maps visible-camera rectangle to HM grid; fever-path refinement mirrors C driver behavior.
  • Calibration: setCompensation({ offset, envSlop, envStandard }) applied to all public temperature outputs.

Protocol highlights (device side):

  • CalcT: {0xA5, 0x55, 0x01, 0xFB} → 7-byte response (peak + grid).
  • QueryT: "QueryT\r\n" → 2054-byte thermal map payload + CRC.
  • SetRect: {0xA9, 0xEE, 0x01, 0xFB, x, y, w, h} → 4-byte ACK.

Note

  • measure() performs multiple CalcT reads with os.sleep(125) between frames; default 8 frames is recommended but increases latency (~1 s for 8 frames).
  • getThermalMap / getRectTemp may return null on UART timeout or CRC/header errors; always guard before accessing .map or .value.
  • Hardware rate and timeout in init({ timeout }) affect reliability under load.

2. Files​

  • dxTemp.js
  • Place dxTemp.js under the project dxmodules directory (same as other dx* modules).
  • Serial access relies on dxUart and device /dev/tty* (or configured path).

3. Dependencies​

  • dxUart — open/send/receive/flush/ioctl for the temperature module UART.
  • dxLogger — logging.
  • os — sleep used between frames in measure.

4. Compatible Devices​

Devices running DejaOS (or the same QuickJS + dxUart stack) with an HM infrared temperature module connected on the configured UART (115200-8-N-1 by default).

5. Usage​

Import​

import temper from "../dxmodules/dxTemp.js";

Lifecycle​

// Optional: override id/path/baudrate/timeout
temper.init({
  id: "tempUart",
  path: "/dev/ttySLB3",
  type: "3",
  baudrate: "115200-8-N-1",
  timeout: 200,
});

temper.deinit();

Compensation​

temper.setCompensation({
  offset: 0.3,
  envSlop: 0,
  envStandard: 0,
});
// finalTemp = raw * (1 + envSlop * (raw - envStandard)) + offset

Multi-frame measurement (measure)​

const stats = temper.measure(8);
// stats: { max, min, avg, samples } or null
if (stats) {
  logger.info("max:", stats.max, "min:", stats.min, "avg:", stats.avg);
  logger.info("per-frame peaks:", stats.samples);
}

Single-frame full-FOV peak (getTemp)​

const t = temper.getTemp(); // number °C or null

Thermal map (getThermalMap)​

const tm = temper.getThermalMap();
if (tm) {
  const c = tm.getPixel(16, 16);
  logger.info("center °C:", c, "raw bytes:", tm.map.length);
}

Face-linked ROI (getRectTemp)​

// rect: [x0, y0, x1, y1] in visible camera coordinates (same as face SDK rect)
const r = temper.getRectTemp(event.rect);
if (r) {
  logger.info("value:", r.value, "fever:", r.fever, "grid:", r.grid);
}

6. Constant Definitions​

Thermal grid and framing constants are internal to dxTemp.js (e.g. 32×32 grid, QUERY_T_TOTAL 2054). Public API does not export a constants object; configure timing via init({ timeout }) and measure(frames).

7. Multi-threading Support​

  • UART receive / send are synchronous from JS; avoid concurrent calls from multiple threads/workers unless your runtime serializes access to the same dxUart channel ID.

8. Important Notes​

  1. Call init() before any read API; deinit() closes the UART.
  2. measure(n) sets full-screen ROI internally; frames is truncated with minimum 1; samples may be shorter than frames if some CalcT reads fail.
  3. getRectTemp triggers SetRect, QueryT, then CalcT; it is heavier than getTemp alone.
  4. Tune timeout (ms) if responses are truncated intermittently.
  5. getThermalMap() returns null on CRC mismatch — do not assume success without a check.
  • dxUart: serial port abstraction used by dxTemp.
  • dxFacial / face worker demos: supply event.rect for getRectTemp.

10. Examples and test scripts​

Source Code