raspi with lcd shield with buttons

[elkvis]

has anyone tried to use the lcd shield with buttons with a raspberry pi? I bought a couple of those, and I'm interested to see if anyone else has tried it, so I can save a bit of time in developing my device.

[adafruit]

we'll have a version for the raspberry pi shortly - it should be code-compatible with the arduino ones - no ETA on release.

[elkvis]

what about using the existing arduino version with the raspberry pi?

[adafruit]

it should be code-compatible with the arduino ones - no ETA on release.

[tldr]

i think the problem's going to be that you'll want to run the display at 5v and the mcp23017 at 3.3v and the board only has a 5v supply. you could use the 4 channel level converter on the i2c lines, i guess.

[elkvis]

according to the link on the manufacturer's website, the mcp23017 is rated to run up to 5.5v, so would it be correct to assume that voltage isn't really a problem?

[tldr]

not to the shield, but maybe to the pi.

not sure if the shield has pullups to 5v, but i assume that that's what r1 and r2 are. don't want the pi seeing that if it does. i know that with the max1307(?) rtc it is suggested that you leave the 5v pullups off of the breakout when using it with the pi. don't know if you could do that with the 23017.

[elkvis]

on a related note, is it especially difficult to reconfigure a couple of the button inputs on the lcd shield to drive LEDs instead? I know the pins on the 23017 can be configured as inputs or outputs, so I'm confident that it's possible, but I'm just wondering if someone has already done it, so that I could avoid re-inventing another wheel.

[tldr]

the only problem will be that the library for the shield includes the mcp23017 object as a private member, so i don't think you can get at the pinMode function.

simplest thing might be to just make the mcp23017 member public, so you could use something like

Code: Select all

// the buttons are on pins 0-4.
  lcd._i2c.pinMode( 0, OUTPUT);
  lcd,_i2c,digitalWrite (0, HIGH);

of course, i'm something of an object oriented ignoramus. mostly i just pretend my sketches are written in c. only occasionally does this lead to my being bitten on the ass.

EDIT : i moved the line

Code: Select all

Adafruit_MCP23017 _i2c;

from the private to the public definitions in Adafruit_RGBLCDShield.h, then included the two lines above in the setup function in the example sketch and it compiled just fine.