EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Flipp on March 04, 2014, 08:24:03 pm
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Hi,
like i have announced in this (https://www.eevblog.com/forum/testgear/dmm-tab-android-dmm-utility/30/) topic, i have played a little with a Bluetooth link module in my CEM DT-9939 multimeter.
(http://www.oscomp.de/Editor/assets/Oscomp/Produktbilder/Messtechnik/Multimeter/CEMDT9999_big.gif)
Step 1:
testing pinout of the original wireless module, it was easy to find TX and RX (2400bps,8n1) as well as switched supply pins.
protocol is explained here (http://www.electronicsinoz.info/extech-ex540-digitech-qm1575-python-decoder/) (basicaly 4 bit byte id and 4 bit data per byte).
Bluetooth module BTM400 aka HC-05 is working and only active while data is sent.
Step 2: make it working with a smartphone app
There are 3 similar meters: EXtech EX540, Digitech/Jaycar QM1575 and DT-9939 by CEM which seems to be the OEM.
And 3 apps: Digitech DMM:
(https://lh4.ggpht.com/-Znnz1BL2BtUhff39Qz9R8DxUe47ZWj8FZBMm9kwTUc9bwXThRrAECQm8dZRGRTabWs=h310-rw)
for Jaycar QM1576 and Meterbox /Meterbox HD:
(https://lh5.ggpht.com/Kbu5Xu551Jc5Qtl-RxMXmADfwJMeH2zJXXnFZy73nG3QW0iAf23bX2RY-a08WTE0whE=h310-rw)
for CEM. Its looking pretty similar, isn´t it?
All Meters share the same serial Protocol. But the smartphone apps wont even connect bluetooth, obviously they decide by the name of the Bluetooth device. After long testing i worked out a semi-working config by giving the HC-05 the name DT-9939. Digitech DMM app find, connect, detect the right meter and deletes unnecessary buttons, decode and display the data correct. But it does not refresh display, so the first reading stays on display.
Has anyone an idea whats wrong in the configuration? It seems to be only one last bit to be discovered.
if i want to look into the Bluetooth part of these apps, how can I do? I can find some bitmap and layout data but no actual program or config.
Flip