Talking to the Protek D620 through Hyperterminal…Normally

RL’s comment on the other Protek D620 article had us thinking – perhaps people DO want to talk to their D620 through the RS232 interface.   Every time we get a new piece of equipment, we just go straight for the JTAG port – heh.   But there is a lot of value to being able to chat with the Protek device normally, if you will.

RTFM, you say?   Funny – that’s what we said as well until we opened the D620 CD and found that there was in fact, no manual about the serial comms details as advertised in the instruction manual.   Lame!   I imagine it’s floating around the interweb somewhere, so if one of you intrepid readers happens to have a copy, please get in touch.

For now, we’ll throw back to one of the basic elements of getting into an unknown system – snooping it’s comms.   In this case, we have the D620 software and will simply run a serial port monitor while we fiddle around with the tool.   Capture a few transactions and we should be ready to go.   So that’s exactly what we did – short story made even shorter, you can put the device into RS232 mode with one hex command.   After that, it will continue to spit out measurements every time it gets a CRLF.

You will probably write some software to do this in an automated manner, but for now we’ll just use Hyperterminal and a hex editor to paste in the “start” command.   Once the meter is ready for serial comms, you can change modes and do all sorts of other things and it will faithfully shoot you a hyperterminal twitter with the measurement you’re currently seeing on the screen.

So fire up hyperterminal (9600, 8, n, 1, no flow control) and connect your meter – let’s get going.

The start command for the D620 seems to be: 02,44,3F,0D.   Translated to ASCII it is: [STX]D?[CR].   Basically just the string “D?” but preceeded by a hex 02, the STX(Start of Text) code and followed up with a carriage return.

Since STX and CR are non-printable characters, it’s hard to copy and paste them.   The easiest way to get it done is to open a new file in a hex editor, type in 02 44 3F 0D and then switch to text mode in order to copy and paste.   Then you’ll get some crazy characters like: –characters removed, they screw up the RSS feed –
You can try and copy/paste directly from this website if you like – you’ll probably need to hit Enter afterwards to add on the CRLF (as good as CR) and execute the command.   The meter should immediately respond with it’s current measurement, for example:

d000- 0.058mVdc

The d000 is the setting, then a dash, then the measurement.   Pretty easy to parse, eh? Toggling through each of the settings (mV, V, Ohm, Cap, Hz, Temp, uA, mA, A) with only a temp probe connected gave the following example outputs:

d000- 0.048mVdc

d010-.00013Vdc

d040 12.539ohm

d075 —-.-uF

d080   0.000Hz

d120         22′C

d140- 0.035uAdc

d170   0.001mAdc

d200 0.0001Adc

So that’s it for now.   There is also a “Stop Measuring” command but who cares, really?   The meter will stop when you turn it off..   In a future article, we’ll seek out the commands to download the internal datalog memory.   With those two items, you should be well on your way to writing a software tool for pretty much any platform.

UPDATE:   Ha!   I just tried pasting the –characters removed– from the webpage above into hyperterminal and it worked!   I’ll be damned – hacking a meter via the web, that’s truly a first here.

UPDATE 2: The hex character 02 screwed up the RSS feed, so it was removed from the article.   Sorry.