ILI9325 circuit requirements?

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rogerparkinson
 
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ILI9325 circuit requirements?

Post by rogerparkinson »

A while back I purchased a 2.8" 18-bit color TFT LCD with touchscreen breakout board - ILI9325 PID: 335 (which I see isn't now available, replaced with something similar). I got it working on a Teensy 3.0 but I needed it to be configured a bit differently to fit it into my project, so more recently I got a 2.8" TFT Display with Resistive Touchscreen PID: 1774 which looks basically the same thing but without the PCB. I'm okay with SMD soldering, I've made a few things and some of them worked :)

What I need to do is put together a similar PCB to the 335, the main difference being that I really need the breakout pins down one edge rather than at the end. I really do have no room in the thing I'm making. Also, I figure, since I know I'm using 3.3V from the Teensy I can leave out the voltage regulators which cope with 5V inputs.

The question I have now is: what do those two 74AC245 ICs actually do? I read the data sheet and it seems to be buffering and something called 'current sinking' which I had to look up. I'd like to leave the two ICs out if possible and connect the Teensy more directly to the 50 pin connector, but I don't want to fry my new screen trying something dumb, and 'current sinking' sounds like it might prevent frying. I've got the breakout board ( Adafruit 50 pin 0.5mm pitch FPC Adapter PID: 1492 ) to try things out on. I've attached my schema, still an early version, in case it is useful.

Thanks for any help
Roger
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zener
 
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Re: ILI9325 circuit requirements?

Post by zener »

Well, the current sinking feature is not actually the fancy part. Current sinking is fairly typical, and you likely don't need that to communicate with the LCD display. The fancy part is the bidirectional control. This can let data pass to the LCD (probably the normal state of things) but can also let the display send data to the CPU. If you never need to read data from the display then maybe you can get rid of the '245. I really don't know if you would typically ever need to read data from the display. The upper '245 in the schematic doesn't seem to have the bidirectionality enabled so you could conceivably eliminate that. However buffers provide some protection to the signal lines and are sometimes used that way.

BTW your power and ground connections for the '245's are not shown on the schematic. Need to "invoke" those.

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adafruit_support_rick
 
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Re: ILI9325 circuit requirements?

Post by adafruit_support_rick »

The buffers are being used as level shifters to reduce the 5V signals from the microcontroller to 3.3V signals for the LCD

rogerparkinson
 
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Re: ILI9325 circuit requirements?

Post by rogerparkinson »

Sounds good, thanks. That's enough information to allow me to breadboard it without the '245s and see if it works.
I'm fairly sure I don't read from the display and I know I don't need to convert from 5V to 3.3V
I'll post the result here.

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