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Topic: Philips bench DMM I2C internal control (Read 118 times) previous topic - next topic

cowasaki

Jun 20, 2018, 05:30 pm Last Edit: Jun 20, 2018, 05:49 pm by cowasaki
I have a couple of Philips PM2525 bench DMMs both of which work but one had it's battery run out and so is now showing as "CAL" but it still reads accurately and both have LCD displays which are beginning to fail.  Now Philips use I2C inside their bench DMMs so that the processor can "speak" to the display driver.  I have seen examples of people reading the display information and using a micro controller to decode this information and display it on a new LCD.

I have the circuit diagram and can locate the I2C stream but if I try and hook an arduino to it then the controller and display driver get confused with this interloper being on the bus when it shouldn't.

So.....

Any ideas how I can read the data off the bus without the display driver IC or micro controller getting upset?  I've had a few ideas such as using an op-amp an a unity gain amplifier and passing this to the arduino but the libraries I've been looking at want to communicate rather than just read.

I got the idea from a similar project where the person doing it uses a different PIC - https://www.maximintegrated.com/cn/app-notes/index.mvp/id/6315

I think the biggest issue may be arduino's libraries wanting to link with the device rather than just decode it.

Riva

Maybe use a logic analyser instead.
Are the DMM's using 5V
Don't PM me for help as I will ignore it.

ieee488

#2
Jun 21, 2018, 12:35 pm Last Edit: Jun 21, 2018, 02:15 pm by ieee488
It seems to have a IEEE488 port.
If it was me, I'd write a Windows GUI program using LabVIEW or VB.NET to communicate with it. You'll need USB-IEEE488 cable which are not cheap.
You should be about to use pyVISA if you know Python.







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