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ST7565 display and app idea

15 January 2012 at 10:59 pm

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Realized that there’s no decent mobile reference-app for Arduino while sitting on the bus the other day, so I’ll spend some time this week making just that. I did a first version using Flex Mobile on friday and it wasn’t very responsive at all. 2 seconds to open a small utility to calculate resistor values? I think not. Will do a version two based on pure AS3 to get that extra speed. I’m eagerly waiting for packages filled with fun Arduino-stuff and electronics from all over the world at the moment, but I had some time tonight to play with the ST7565 display from Adafruit today.

It was very easy to get up and running using this tutorial from Ladyada but there’s one major omission in this kit. The screen cannot take more than 3.3 volts on the IO pins so to ensure people don’t damage the screen, the nice people on Adafruit have included a NXP HEF4050BP chip that will reduce up to 6 signals to a safe 3V output. The tiny detail that someone missed is that for this RGB screen, you need 7 signals to fully drive the RGB color display. It’s not a problem for me as I got to do the testing I wanted though only in either R, G or B 😊

What I was curious about is at what speed can my Arduino Uno drive such a screen? Testing showed that it does about 2 fps with only few pixels updating. I had hoped for higher speed and maybe building a quick 2-player Pong-game using two encoders and this screen. At 2 fps, it’s not worth the effort. I’m not too good at C, but the library looks quite efficient. The screen buffer is a 128x64 byte-pattern that you change using bit-math. If you set the first byte to 0x1, you’ll turn on the pixel at 0,7 (x/y). If you set it to 0x2 you’ll turn on the pixel above (0,6) and with 0x3 you’ll turn on both. Fairly simple, but you’d probably want to make some app that could convert bitmaps to these HEX series. The library that comes with it also contains a 5x7 pixel LCD font

The coolest about this LCD was actually the 4050 IC that came with it! Since I’m so new to electronics, I didn’t even know such ICs existed and this one is sure going to come in handy! From what I understand it can take anything requiring 3v and make sure that anything up to 15v is converted down nicely. Very useful!