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)
we got it:
ReplyDelete00 00 00 4C 99 E2 F6 FE 0E A4 62 2A 76 00 11 52 42 CA 9C FC : 22.1
00 00 00 4C 99 E2 76 FC 0A A4 C6 2A 5A FE F6 FA 52 2E 5E DA : 32.2
00 00 00 4C 99 E2 8A 06 10 7A 49 99 C8 1D 00 0A 42 16 CE FE : -11.8
00 00 00 4C 99 E2 A6 EE 0A A4 66 2A 7E F2 F6 F2 52 3E 36 F3 : 77.0
how to decode?
Good job!
DeleteI did a temperature sweep from 20C to 400C using a heat plate (kitchen stove). I lost my results in a HDD crash, but still remember something. 16 bits was used to represent values of min/max/avg/etc. values. When plotting each 8-bit value separately, it was easy to find matching lsb and msb.