Author Topic: Metrix MX24 DMM come join the hack  (Read 518 times)

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Offline shakalnokturn

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Metrix MX24 DMM come join the hack
« on: June 12, 2019, 12:24:46 am »
One of my recent buys was another DMM just because it was cheaper than I usually see them sell for, it came with original box, leads and manual.
Before putting it up for sale I thought I'd play with it a little and peep inside.

While this meter uses the venerable DMM5 ADC and and the right LCD, as it is capable of 50k count for frequency, it seems like Metrix (or was it already C.A.?) decided to cut costs right down and not bother with 50k counts for all other measurements.
No doubt the 0.3% accuracy, lack of precision resistor network were a good enough justification for this, a real shame when the 10 years older MX54 ASYC2 meter using the same ADC performs better.

Anyway, the highest model of the range, the MX26 has the same not so impressive specs but it also has RS232/IR communication as well as some of the other nice features that were available on the older models...
I had a quick look at how possible it mat be to add communication (think Bluetooth) to this model.
The MX26 manual tells you to hold Pk+/- and backlight buttons while turning the DMM on, this should briefly display "RS232".

The MX24B has no Pk+/- key, holding the equivalent position Min/Max and backlight keys seems to display the firmware version. ("01.04" here)

Then looking at the PCB there are a few large pads looking like test points, but then I'm thinking: The build of this thing is so ugly for all we know the IR interface could be an optional board wired in or on spring contacts, as that's already the case for the backlight.
A little probing around determined there were 2 inputs, one pulled high by 68k \$\Omega\$ resistor and an output.
Pulling one of the inputs low while powering on gave a "RS232" message on the display, after that I quickly threw my cheap prolific USB to TTL serial cable on the remaining I/O's and fired up the SX-DMM software.

The software will accept it as a MX26 model (meaning) that the DMM actually responds with a status. No way to log data though, for any measurement the software always returns "The position of the rotary switch is not ready." which is what you normally get when the rotary switch is in the wrong position.

So now I'm stuck there with a little frustration.
Anyone with internal photos or 93C46 dump of a MX26 is welcome!
« Last Edit: June 12, 2019, 12:28:21 am by shakalnokturn »

Offline shakalnokturn

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Re: Metrix MX24 DMM come join the hack
« Reply #1 on: June 13, 2019, 12:24:14 am »
No need to get too passionate about this stuff.
Maybe member PetrosA could chip in, he must be the only one around here with a MX26.
I took the waste of time a step further and looked how the MX24B responded to the "status request" command on different selector positions.

V low Z___    D8   59   76   F6   D6   F6   D6   B6   F6   D6   F6   6C   36   56   0F   00
V ac+dc___   D8   B2   36   F6   D6   F6   D6   B6   F6   D6   F6   6C   36   56   0F   00
V dc______   D8   B2   F6   F6   D6   F6   D6   B6   F6   D6   F6   6C   56   56   0F   00
ADP______   D8   B2   F6   F6   D6   F6   D6   B6   F6   D6   F6   6C   56   56   0F   00
Hz_______   D8   B0   B3   63   B6   F6   D6   B6   D6   D6   F6   6C   76   56   0F   00
Continuity      D8   F6   96   EC   F6   F6   F6   B6   F6   D6   F6   6C   36   56   0F   00
Ohm_____    D8   F6   36   EC   56   F6   D6   B6   F6   D6   F6   6C   16   56   0F   00
Capa_____   58   F6   16   EC   F6   F6   D6   B6   F6   D6   F6   6C   16   56   0F   00
Diode____    58   F6   56   EC   D6   F6   F6   B6   F6   D6   F6   6C   36   56   0F   00
500mA___    D8   58   F6   F6   96   F6   F6   B6   F6   D6   F6   2C   36   56   0F   00
10A______   58   AC   F6   F6   56   F6   F6   B6   F6   D6   F6   6C   36   56   0F   00

The responses don't really fit in with the (older than this meter) ASYC2 remote programming manual I have.
« Last Edit: June 13, 2019, 12:33:23 am by shakalnokturn »

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