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Sunday, December 4, 2011

H65 Infrared Thermometer from DealExtreme

DealExtreme is selling an infrared thermometer with measuring range of -20°C ~ 530°C. I bought that for generic use, but was positively surprised by the fact that it had a serial interface hidden inside.


There is a 6-pin male header at the battery compartment. It has 2.00 mm spacing instead of common 2.54 mm. I was using this type of connector to create a cable for testing.

There are clear markers on the PCB, if you take a closer look.


After some measuring, they seem quite logical, see table below. And if you google for MS6530 you will find a Mastech meter with quite identical specifications. With 4x the price. There are also models with A and B suffix having different temperature ranges. High-end models MS6550A and MS6550B are coming with USB data cable. Maybe with same protocol as this one ?

Number Label Description
1 G Ground (Battery negative terminal)
2 V Vcc (Battery positive terminal)
3 I
4 R RX (Meter RS-232 receive pin)
5 _
6 T TX (Meter RS-232 transmit pin)

This meter seems to have RS-232 Interface with 0/5V Voltage levels (Idle 5V). Looks like the configuration is 9600/8/N/1. Transmission is binary format and no specifications available AFAIK. However, I have made some observations.

When meter is powered off and trigger is pushed quickly, 2 measurements are performed. They are transmitted (and measured) with delay of 1.06 s.

Packets are usually 22 bytes long. Sometimes 16. They all start with bytes 0xFE 0xFE (Assuming LSB is sent first).

Some examples:
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 21 22 
----------------------------------------------------------------- 
FE FE 31 34 0F 07 34 00 2D 0D A3 37 1B 00 09 01 08 01 FB 00 D1 F0  T:26.4C A:26.4C
FE FE 31 34 0F 07 39 00 30 0D B9 37 1F 00 0C 01 08 01 F9 00 43 F1  T:26.8C A:26.8C
FE FE 31 34 0F 07 39 00 36 0D AE 37 20 00 0D 01 09 01 FA 00 8D 0A  T:26.9C A:26.9C
FE FE 31 34 0F 07 3C 00 30 0D A6 37 22 00 0E 01 08 01 FB 00 EC 07  T:27.0C A:27.0C
FE FE 31 34 0F 07 3A 00 34 0D B0 37 21 00 0E 01 09 01 FA 00 D6 51  T:27.0C A:27.0C 
FE FE 31 34 0F 07 3B 00 37 0D AC 37 23 00 0F 01 0A 01 FB 00 65 15  T:27.1C A:27.1C 
FE FE 31 34 0F 07 3F 00 32 0D B2 37 25 00 11 01 09 01 FA 00 8D FE  T:27.3C A:27.3C
 
(continues)