CEM DT-8852
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 | |
| Status | in progress |
|---|---|
| Connectivity | USB |
| Frequency range | 31.5Hz - 8kHz |
| Measurement range (A) | 30dB - 130dB |
| Resolution | 0.1dB |
| Accuracy (94dB@1kHz) | 1.4dB |
| Frequency weighting | A, C |
| Time weighting | F, S |
| Standards | IEC 61672-1 Class 2 |
| Website | cem-instruments.com |
The CEM DT-8852 is an IEC 61672-1 class 2 compliant sound level meter with USB connectivity.
See CEM DT-8852/Info for more details (such as lsusb -vvv output) about the device.
Some random facts:
- The device only starts logging to USB when the SETUP key is pressed on the keypad. This also disables auto power-off mode.
- Consumes 9.5mA, regardless of USB or recording status; 15mA when the backlight is on.
- The battery low warning starts when the battery delivers less than 7V.
- Sound pressure level measurements are sent to the host at a rate of 20Hz.
Hardware
- Holtek HT49R70A microcontroller
- Silicon Labs CP2102 USB-serial interface
Photos
Device, front
Device, back
Device, side
PCB
PCB: keypad and LCD
PCB detail
PCB detail
Microcontroller
CP2102 USB interface chip
Protocol
The device communicates at 9600 baud, no parity, 8 data bits, and 1 stop bit (9600/8n1).
Current settings and measurements are continually streamed over the serial bus. Data is encapsulated in packets of between two and five bytes. The packets are structured as follows:
| 1 | 2 | 3 | 4 | 5 |
| 0xa5 | Token | Data | ||
The number of data bytes depend on the token. These are the tokens:
| Token | Data | Description |
|---|---|---|
| 0x02 | 0 | Time weighting Fast |
| 0x03 | 0 | Time weighting Slow |
| 0x04 | 0 | Max hold mode |
| 0x05 | 0 | Min hold mode |
| 0x06 | 3 | Current time in BCD; first nibble unknown |
| 0x07 | 0 | Current measurement is over measurement range high threshold |
| 0x08 | 0 | Current measurement is under measurement range low threshold |
| 0x0a | 0 | |
| 0x0b | 1 | |
| 0x0c | 0 | |
| 0x0d | 2 | Current measurement as shown on the display, multiplied by 10, in BCD |
| 0x0e | 0 | Live measurements mode (not max/min hold) |
| 0x0f | 0 | Battery is low |
| 0x11 | 0 | |
| 0x19 | 0 | |
| 0x1a | 0 | |
| 0x1b | 0 | Frequency weighting dBA |
| 0x1c | 0 | Frequency weighting dBC |
| 0x1f | 0 | |
| 0x30 | 0 | Measurement range 30-80 dB |
| 0x40 | 0 | Measurement range 30-130 dB (auto) |
| 0x4b | 0 | Measurement range 50-100 dB |
| 0x4c | 0 | Measurement range 80-130 dB |
Resources
TODO.