Capacitive touchscreen schematic and documentation

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Timmmm
 
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Joined: Wed May 01, 2013 4:22 pm

Capacitive touchscreen schematic and documentation

Post by Timmmm »

Hi,

The schematic for the capacitive touchscreen (this one: https://learn.adafruit.com/adafruit-2-8 ... -shield-v2) is missing. The resistive one is there (though it is a barely readable bitmap - PDF?)

Also the documentation is unclear on the SDA/SCL pins. It does say that they are connected to A4 and A5, but this is actually not true! They are connected to the pins marked "SDA" and "SCL" on the Arduino (what would be pins 16 and 17). There are solder jumpers on the board (not mentioned anywhere in the documentation as far as I can see) to internally short SDA/A4 and SCL/A5 (or whichever way around it is).

I believe on the Arduino Uno, those shorts are done internally, but I am not using an Arduino Uno so it took me quite a while to figure out why it wasn't working (actually I still haven't got it to work, but that didn't help).

Please can you:

1. Post the capacitive schematic (as a PDF!)
2. Add a note clarifying which pins SDA and SCL are connected to.
3. Add a note about the "<R3" solder jumpers.

Cheers,

Tim

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Franklin97355
 
Posts: 23910
Joined: Mon Apr 21, 2008 2:33 pm

Re: Capacitive touchscreen schematic and documentation

Post by Franklin97355 »

The Eagle files for this shield are here https://github.com/adafruit/Adafruit-2. ... eld-v2-PCB we don't have a PDF version of that file. If you don't have Eagle you can download a free copy here.As to SDA and SCL they are the i2c pins and will go where ever they are on your processor. On the Uno they are in the right place by default. Where is the reference to the "R3" Jumper?

Timmmm
 
Posts: 5
Joined: Wed May 01, 2013 4:22 pm

Re: Capacitive touchscreen schematic and documentation

Post by Timmmm »

Thanks. The "<R3" solder jumper is at the bottom-right corner of the board (next to the A5 pin). It is labelled "I2C jumpers for <R3" and is referring to the fact that Arduino Uno boards before revision 3 don't have the SDA/SCL pin sockets near D13 which are internally connected to A4/A5 - so you can instead short the solder jumpers to connect the touchscreen I2C signals to A4/A5 instead of SDA/SCL.

They aren't mentioned in the documentation at all. But they are clear in the schematic. I've attached a PDF (zipped because PDFs aren't allowed for some reason?).
Attachments
Adafruit touchshield schematic 2.3.pdf.zip
(20.98 KiB) Downloaded 43 times

Timmmm
 
Posts: 5
Joined: Wed May 01, 2013 4:22 pm

Re: Capacitive touchscreen schematic and documentation

Post by Timmmm »

By the way, it would be really really great if in the next version of this board you could add optional pullups to 5V. Even just unpopulated pads for two hand-solderable 0805 resistors would be good. A way to bypass the level shifter would also be good, though it does work with 3.3V boards if you just add 5V pullups to the I2C pins.

All mBed boards are 3.3V and don't have pullups to 5V. At most they pull up to 3.3V but the level shifter on the shield means this is insufficient. Edit: scratch that, it does work with 2.2k pullups to 3.3V.

PS: Your captcha is trivial to break.

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