Colead SL-5868P

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Colead SL-5868P
Colead SL-5868P.png
Status supported
Source code colead-slm
Connectivity RS232
Frequency range 31.5Hz - 8kHz
Measurement range (A) 30dB - 130dB
Resolution 0.1dB
Accuracy (94dB@1kHz) 1dB
Frequency weighting A, C, Flat
Time weighting F, S
Standards IEC 651 Type 2, ANSI 1.4 Type 2

The Colead SL5868P is a sound level meter with RS232 connectivity.

It has live (Lp), equivalent continuous (Leq), and threshold-based (Ln) measurement modes. It can also trigger alarm conditions based on a configured level, and drive a relay accordingly.

It is rebranded under many names, but appears to generally have the SL-5868P model designation. It's available for under $100.




The serial port is set to 2400bps, 8 bits, no parity, 1 stop bit (2400/8n1).

The meter sends two measurements per second. When a new measurement is ready, the device sends 0x10. The PC responds with 0x20, which causes the device to transmit a 10-byte structure containing configuration and measurement.

When the user presses the Read key on the keypad, the device sends all its stored measurements out via the serial port. This is preceded by two bogus measurement records as a marker, where all the digits are set to 0x0a and byte 2 contains 0x09 in the first record, and 0x08 in the second record. The stored measurement records then follow; the entire sequence is typically repeated twice, including the marker.

When the user switches back to live measurement mode, another two bogus measurement records are sent. To mark the return to live mode, the second bogus record this time contains 0x07. All following records are then live.


Command Direction Description
0x10 Device -> PC Measurement ready
0x20 PC -> Device Send measurement

Data structure

Byte Value Description
0 Always 0x08
1 Always 0x04
2 Configuration. The low nibble has the following meaning:
0000 Lp, Weighting A, Fast
0001 Lp, Weighting A, Slow
0010 Lp, Weighting C, Fast
0011 Lp, Weighting C, Slow
0100 Lp, Flat, Fast
0101 Lp, Flat, Slow
0110 Ln, Weighting A, Fast
0111 Ln, Weighting A, Slow
1000 Leq, Weighting A, Fast (10-second mean)
1001 Leq, Weighting A, Fast (mean over minutes)
1010 Leq, Weighting A, Slow (10-second mean)
1011 Leq, Weighting A, Slow (mean over minutes)
1100 Internal calibration mode, Fast
1101 Internal calibration mode, Slow
1110 Unused
1111 Unused
The high nibble has the following meaning:
0001 Normal measurement
0010 Max hold mode
3-7 BCD-encoded value, one byte per digit 0x00-0x09. 0x0a means ignored digit. The last digit represents the decimal.
8 Measurement status
0 Invalid
1 Valid
9 Checksum: sum of bytes 0-8