Tuesday, January 7, 2014

RGB LCD Backpack

I'm a little torn about this.

I've been buying my RGB LCD backpacks from Chris over at the OpenEVSE store. The downside of this is that when people want an EV Sim or a reflow oven standalone controller, they can't just do one-stop shopping. Additionally, if I had an absolutely free hand, there are a couple of tweaks I'd make to the design:

  1. LiquidTWI2 supports a piezo element on the last unused pin of the MCP23017. It'd be nice if there was a spot on the backpack for that.
  2. There's probably a simpler layout for the button pin connections.
  3. I want to include a 2 way solder jumper for the backlight common pin to accommodate both common cathode and common anode backlit modules.
  4. Since I happen to have a pile of them, I'd use the SSOP derivative of the MCP23017 instead of the SOIC one. That leaves more room (should it be desired) to add stuff down the road (for example, Chris added a Dallas Semi i2c RTC chip to his).

So I've posted a design for my own version of the i2c RGB backpack. It feels slightly, I dunno, mean to steal his thunder like this. I'm not really trying to take food from his mouth or anything like that. My own latest trend has been to replace ATTiny85 + MCP23017 designs with ATTiny84s directly wired to the LCD. It saves quite a bit of firmware space, and about a dollar off the price, and for most of the designs to which I've applied this, the RGB backlighting hasn't been needed anyway.

But once the prototype comes and the design is validated, I'll add my version of the backpack to my square-up store just so folks won't have to buy from two different places. The i2c connection will be pin-compatible with the OpenEVSE backpack, and it'll work with the LiquidTWI2 library. If you want to take a look at the board, the design is in my OSH Park profile.

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