Mastech MS8229 RS232 Hack

[lindworm]

Hey guys,

some time ago I was able to get hold of a Mastech MS8229 multimeter for 25€ and grabbed it right away.
After watching Daves video about what makes a good meter I'm still happy with it.
It may not be as good as a Fluke, but it seems to cover the main points that make a reasonably usable meter.

So while browsing at hackaday.com I got exited about Craigs RS232 multimeter hack. So I cracked my Mastech MS8229 open, but wasn't able to find a hint that the IC is actually from CyrusTek.
The controller is covered under a blob of black plastic and after some measurements it became pretty obvious that the layout doesn't have anything to do with the CyrusTek IC series.

However I wasn't willing to give up and after some serious waste of time investigation I found out, which IC is used in the Mastech MS8229:
It's a Fortune Semiconductor branded one. The exact model is FS9721-LP3 and the datasheet can be found here.

After getting hold of the datasheet it became pretty obvious that this was going to be quiet easy, as the Fortune chip has a pin (pin 84, 4th from the top on the left side) that has to be pulled to ground as long as you want to transmit data over the serial port.

I did so and viola, my little 1052E spit out some digital data and stopped doing so as soon as I disconnected pin 84 from GND.

Success! There's the RS232 indicator on the display, after grounding pin 84:


On page 15 of the datasheet is a whole diagram which provides all you need to know:
Wire pin 64 to an optocoupler and connect the other pad of the optocoupler to a resistor connected to VDD (not GND!).
Then wire the reciever part of the optocoppler between pin 2 and 4 of the RS232 port using another resistor.

I only had some nice optocouplers that I salvaged from old nics and didn't want to waste them, so I used an infrared LED and an infrared phototransistor.

To actually measure your serial signal you should connect GND of your scope to pin 5 (not 4!) and you can measure your signal at pin 2 (if you didn't mess up the optocoupler stuff).


Here's an image of the wiring (don't take too short wires as I did...). The black glob at the serial port holds my cheapass optocoupler.


You may find a better place to put the serial plug, I had to remove a 3pin socket and lay down a little cap and an oscillator to make everything fit when the lid is closed again. (Check out if there's high stuff on the pcb where you want to place your port _before_ you cut the hole...)

Well, what to do now with this digital garbage we get out of the serial port? As expected, the protocol is described in the datasheet.
But beeing lazy, I did a quick search on google and actually found out that someone already implemented it:
Push me hard!

It's in German but should be quiet comprehensible with google translate.

So now we have everything we need to get the data out of this baby over RS232.

Here are some snapshots of my implementation:
The whole thing:


The on/off switch that controls RS232 transmission and a female RS232 plug..DOH! Should've used a male one...now I have to solder an male-male adapter cause I don't have a male to male serial cable -.-


And everything reassembled:



If you have questions, feel free to ask.
Otherwise: Happy hacking!

[trustfm]

Thanks for sharing ! I have also done this hack but i get 14 bit stings as output but does not comply with the documented format
I get something like this in ohm range :
02 00 20 06 18 4C 70 00 00 00 20 80 80 C0
The last 4 bytes are always the same and is strange.

 

[trustfm]

Later : i have resolved by adding instead of a 1K resistor at the emitter a 10K resistor and i have used a toshiba optocoupler.
I have made a datacapture sw dedicated for this multimeter. I will finilize it and post it here in order to download it .

Thanks !   

[trustfm]

As i said here : http://www.trustfm.net/GeneralTools/DMMDataLogger.php you can find the sw data logger for this meter.
Supports rel and hold buttons
Works under win & linux
Enjoy ! 

[brainwash]

Thanks for the hack, it inspired me to buy one (for logging only, it's pretty crap as a general purpose multimeter) and perform something similar:

http://hackcorrelation.blogspot.de/2015/10/adding-isolated-data-output-to-mastech.html




I've transplanted the complete USB/UART transceiver inside the unit:

[trustfm]

Great news !!!
I have added a post at my facebook page about your hack !