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Topic: Quick tip on a I2C LCD 2X16 with PCF8591T ?!! (Read 300 times) previous topic - next topic


The display lights up, but I cannot get it to show any letters. I´ve tried both the A4,A5 and the dedicated SDA,SCL pins - but no I2C scanner code can identify the I2C device and address and no code works for showing characters no matter what libraries used.

Arduino Uno R3


This chip? https://www.nxp.com/docs/en/data-sheet/PCF8591.pdf
I doubt that you can drive an LCD with it.

But a I2Cscanner should find it. Are there pullup resistors in the SDA and SCL lines?
Power and ground connected?


I admit - it feels a little bit strange.

It´s a swedish retailer selling it: https://www.kjell.com/se/sortiment/el-verktyg/elektronik/optokomponenter/led-lcd-displayer/luxorparts-lcd-display-2x16-seriell-i2c-p90786

In their catalog picture it shows a PCF8574AT chip. When buying it instead there´s a PCF8591T mounted.

And it doesn´t seem to work?!


Lots of Retailers deliberately lie.
In this case it looks as if the Manufacturer assembled the wrong chip and the Retailer did not realise that she had got some faulty items.

I would have a full and frank discussion with the Retailer.   Get a replacement immediately i.e. LCD with backpack.

In case you did not realise,  the PCF8591 is a DAC / ADC chip.    Completely different function.



Jun 10, 2018, 04:21 pm Last Edit: Jun 10, 2018, 04:21 pm by floresta
But a I2Cscanner should find it. Are there pullup resistors in the SDA and SCL lines?
Not really.  The photo shows a familiar I2C adapter board with a circuit designed for a PCF8574 series chip.  These chips have the SCL and SDA connections on pins 14 and 15.

If the board was actually populated with a PCF8591, which has its SCL and SDA connections on pins 10 and 9, then the scanner will obviously not detect it.

Its time to contact your retailer.



Thanks a lot for your really competent answers - from all of you! I´ll contact the reseller and we´ll see what they´ll have to say about it!!



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