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EEVBlog 121GW Multimeter Firmware Details
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tpw_rules:

--- Quote from: firewalker on August 14, 2018, 08:26:43 pm ---The offset number is directly added to the adc result? Is the function that involves the values read form the adc, the calibration data and the displayed number known?

--- End quote ---

Yeah, it's all detailed in the reverse engineering. I suggest you consult that if you are curious because I'm too lazy to explain everything. But to put it in a sentence, bargraph = (ADC - offset) * gain, and screen = smooth(average(bargraph) - nonlinearity_corr), where average is the average of 8 or 16 bargraph samples, nonlinearity_corr is some nonlinearity offset calculated using some data tables and the listed coefficients in a manner that I don't entirely understand, and smooth is a rolling average that resets if the difference between samples is too large.

May I ask why you are interested in knowing all this?
firewalker:
I was wondering if it is possible to recalibrate offset by hand editing the calibration data. Because someone (Dr. Frank) mentioned that someone might have to complete and the full scale gain calibration in order the meter to save and accept the zero offset data. But this mean specialized equipment.

Alexander.
tpw_rules:

--- Quote from: firewalker on August 14, 2018, 09:12:55 pm ---I was wondering if it is possible to recalibrate offset by hand editing the calibration data. Because someone (Dr. Frank) mentioned that someone might have to complete and the full scale gain calibration in order the meter to save and accept the zero offset data. But this mean specialized equipment

--- End quote ---

It would be possible. However, according to my knowledge of the firmware, the corresponding factor is saved before the G-END or OFF-E message is displayed. So you can just turn off the meter after offset calibration to skip gain calibration. But of course, the offset factor is used when calibrating the gain factor, so one would be advised to do gain as well. Maybe someone can work out the math to adjust the gain factor, and hand edit that in.
Lion_Tamer:
Hi all

I have finally had time to sit down and start playing with the meter properly, although I would love to have completely open source firmware I also know that I don't have the skill or knowledge to write it, I also don't have the time or equipment to do the extensive testing required but thought that I could contribute by at least dumping out the firmware from the BLE112 blue tooth module (I know that at least Joe has a meter with an un-programmed module and though it would be useful in case anyone bricks one).

I did this using the "Texas Instruments Smart RF Flash Programmer" software with a "CC Debugger" connected to the CN2 port in the 121GW - connections as below:

121GW <=> CC Debugger
Pin 1 <=> Pin 7
Pin 2 <=> Pin 2 + 9
Pin 3 <=> Pin 1
Pin 4 <=> Pin 3
Pin 5 <=> Pin 4

In time I may try to reverse engineer it a bit more but I suspect that my lack of expertise will hinder me there.

Jem

P.S. this was dumped from meter no 180701854 running firmware version 1.26
Lion_Tamer:
I found that I was struggling to understand the official Packet protocol document so as I don't currently have a blue tooth interface for the PC I have been looking at the UART streams between the STM32 processor and the BLE112 blue tooth interface on the meter and am slowly creating a more detailed document about the 19 byte packet.
I have attached what I have got so far below along with a screen shot of a packet as captured from my meter.

Note: Meter Firmware Version 1.51

Jem
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