Help with Hyundai LCD


New member
Hi everyone,

I recently purchased a Hyundai HG25504 LCD screen from AllElectronics. I plan to control this with an Atmel Atmega32 microcontroller connected via UART.

I connected the data pins of the LCD to PORTC, and the control pins to PORTB. For the negative voltage required by the LCD, I am using a MAX233, which gives me about -10v (according to the datasheet using this to power external devices is ok). The rest is 5v, using a 7805 from 12v.

Just to test the connections I output 0b010101 on all microcontroller ports and measured the voltages on the LCD connections to verify, however on some pins I'm getting around 3.5v when it should be high, while others seem ok (around 4.75v). The lows seem ok also (around 0.5v).

When I disconnect the LCD from the microcontroller and measure directly, the output voltage is ok again.

Any ideas of what causes this? From my experience I think this is a fanout issue, however from the datasheets and other projects that use this LCD it seems ok to just connect them directly. Could the LCD be faulty?

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New member
You are right!

For this test I connected /RD to 1 and /WR to 0 and all the voltages were correct.

Thanks for the help.