I have a couple of Philips PM2525 DMMs (as seen in image 7). Both work but one is showing a CAL error due to the battery running out (now replaced) and both have leaking LCDs. The brown one has a lesser issue to the white one and it also has no CAL error.
I found an article regarding reading the I2C data that goes to the LCD driver by using a MAXQ615 (
https://www.maximintegrated.com/en/app-notes/index.mvp/id/6315). I, however, have no experience of this device but I do have experience of the Arduino so would like to use that device.
The cable connecting the front panel to the main board is a 7 way ribbon cable (as seen in image 2) and I have replaced this by two cables plugging into a breadboard (as seen in image 3) in order to give me a breakout.
I also have the service manual (
https://doc.xdevs.com/doc/PHILIPS/PHILIPS%20PM%202525%20Service.pdf). This shows the I2C bus (as seen in image 4).
The IC that controls the display is the PCF8574 (
https://www.nxp.com/docs/en/data-sheet/PCF8574_PCF8574A.pdf).
Looking at the 7 way cable with the logic analyser (as seen in image 5) there is data on lines D2 & D3 and from the pinouts (from the right)
D0 VSS (IC pin 8 )
D1 VCC (IC pin 16)
D2 SDA (IC pin 15)
D3 SCL (IC pin 14)
D4 ?
D5 ?
D6 INT neg (IC pin 13)
So using the article I should be able to read SDA & SCL from D2 & D3 of the data cable.
So I got this far..... If I connect the Arduino to the SDA & SCL then initialise the I2C library it resets the PM2525. I assume that the library is either pulling the line(s) high or low rather than simply reading it.
I only need to actually READ the data. Does anyone have any ideas?
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