Metrix MX24 DMM come join the hack - Page 1
Forum section: electronics / testgear

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 12, 2019, 12:24:46 am
content: 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 ADCandand 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 68kresistor 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!

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 13, 2019, 12:24:14 am
content: 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 00V ac+dc___ D8 B2 36 F6 D6 F6 D6 B6 F6 D6 F6 6C 36 56 0F 00V dc______ D8 B2 F6 F6 D6 F6 D6 B6 F6 D6 F6 6C 56 56 0F 00ADP______ D8 B2 F6 F6 D6 F6 D6 B6 F6 D6 F6 6C 56 56 0F 00Hz_______ D8 B0 B3 63 B6 F6 D6 B6 D6 D6 F6 6C 76 56 0F 00Continuity D8 F6 96 EC F6 F6 F6 B6 F6 D6 F6 6C 36 56 0F 00Ohm_____ D8 F6 36 EC 56 F6 D6 B6 F6 D6 F6 6C 16 56 0F 00Capa_____ 58 F6 16 EC F6 F6 D6 B6 F6 D6 F6 6C 16 56 0F 00Diode____ 58 F6 56 EC D6 F6 F6 B6 F6 D6 F6 6C 36 56 0F 00500mA___ D8 58 F6 F6 96 F6 F6 B6 F6 D6 F6 2C 36 56 0F 0010A______ 58 AC F6 F6 56 F6 F6 B6 F6 D6 F6 6C 36 56 0F 00The responses don't really fit in with the (older than this meter) ASYC2 remote programming manual I have.