EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: The Soulman on November 21, 2016, 10:08:43 pm
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I'm looking at getting a new meter for hobby use, that would involve small electronics up to electric
vehicles, at the day job I have a fluke 175 not to impressed with that.
Some searching brought me to the uni-t ut61d a 6000 count meter that does everything
I need but am not to convinced on the overall build quality and durability (occasional outdoor and what not).
I do like the IR/rs232/usb connectivity that would allow me to capture battery charge/discharge voltage or current.
Luckily there is also the (200 euro) Gossen MetraHit 2+ based on the same main processor
but with less feature's enabled including no user usable IR interface, for that you need to get the MetraHit World (350 euro) that also has the same full feature's as the ut61d but the IR interface is proprietary and only will work
with the optional usb-Hit interface (aprox. 250 euro) and Metra-win software (aprox. 200 euro) that adds up
to 800 euro's so not hobbyist budget friendly..
Anyway my interest goes out to the 2+ apart from IR connectivity it does what I need and seems rugged enough.
As can be seen in pictures from this thread:
https://www.eevblog.com/forum/testgear/ebay-gossen-metrahit-2-neglected/ (https://www.eevblog.com/forum/testgear/ebay-gossen-metrahit-2-neglected/)
The main processor is the FS9922-dmm4 from Fortune:
http://www.hobbielektronika.hu/forum/getfile.php?id=270789 (http://www.hobbielektronika.hu/forum/getfile.php?id=270789)
The datasheet shows to enable the rs232/ir it only takes a 1k resistor and a ir-led, press the REL button more than 2 seconds and the rs232 switches on and the auto power-off (fixed at 15 minutes) is disabled
that is also the only way to disable auto power-off.
The ut61d and other meters with the same chip work like that and plenty of free software available from uni-t, peak-tech, sigrok and others.
The Metrahit 2+ is slightly different it has auto power-off at 10 minutes but that can be defeated.
And it uses less buttons (4 instead of the usual 6) and in a different way this is probably done
by the additional microprocessor that also handles bidirectional factory IR (for calibration?)
and probably does some more need stuff as well.
The only way for the 2nd microprocessor to influence the readings (as calibrated) of the main chip
is for it to manipulate the reference voltage separately for each of the different ranges
for that it also needs feedback from the main chip, only way possible is the rs232 interface..
So that must be enabled all the time, is it possible to tap into that and send it to the outside world??
To me it makes perfect sense if this meter works this way, like this they can share the entire
board and components across four different models this 2+, the dmm15 (=2+ without back light and rubber holster), the most expensive (off the four) full-featured metrahit world and the dmm16 (=world but without rubber holster and not able to use the 450 euro interface/software combo).
So anybody looked into this before, is it worth looking into?
I would be happy if I could get rs232 data from main the chip, others might be interested if it is possible
to hack a 175 euro dmm15 into a 350 euro metrahit world??
Ideas and input much welcomed.
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Spent some time probing around, also found the microprocessor is a 32 pin atmega328p and has programming port on the pcb..
The serial output from the fortune chip is always enabled when the meter is turned on.
However I wasn't able to track the signal to any of the 328p pins or the ir led. :-/O
Edit: Found it, its pin nr. 32 (PD2)
Making a serial output could be as simple as adding a single IR led (could be glued on top of the existing IR tx/rx combo and shine out the same IR transparent window on the top of the enclosure) and a resistor and have it always turned on when using the meter.
A better solution would be using the existent hardware and reprogramming the 328p somehow to activate the IR thru a key combination.
Overall I'm very pleased with this meter (and prefer it over the fluke 175 any day of the week) but still would be really cool
to use IR serial output and lengthen the back-light (that is controlled from 328p) duration from (fixed) 1 minute to perhaps an hour.
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The only way for the 2nd microprocessor to influence the readings (as calibrated) of the main chip
is for it to manipulate the reference voltage separately for each of the different ranges
for that it also needs feedback from the main chip, only way possible is the rs232 interface..
That assumption turns out to be correct, here are the references voltages in milivolts on fs9922dmm4 chip pin nr.4 of my meter:
DC:
600mV 635,8
6V 635,8
60V 635,8
600V 635,8
60mA 642,1
600mA 643,5
6A 637,8
10A 635,8
AC:
600mV 641,0
6V 638,8
60V 636,8
600V 636,8
60mA 658,6
600mA 653,3
6A 652,3
10A 652,3
Measurements are taken with a (known to be accurate) Metrawatt MA5D and are repeatable and double checked for typo's as this data might come in handy in the future. ::)