RPN-duino

[Chasfield]

Attached is a schematic for the two line RPN-duino calculator.

1602 LCD module
The version I used has a built-in 100 ohm current limiting resistor for the back-light. I added in a further 220 ohms to throttle it back a bit for the sake of battery life. I read that some similar modules don't have a built-in resistor and, in that case, the back-light LED will fry itself in short order if you don't fit one. The 1602 takes up six of the Arduino's digital I/O pins - two for control and four for data bits. The R/W pin on the module is grounded to configure its control registers for write only operation.

Arduino
The five keyboard row lines use pins A0-A4. These are analogue ports by default but are configured and referenced using their digital I/O aliases (D14-D18) by the Keypad library. Column lines use regular digital I/O ports.

I have attached the most up-to-date version of the source code, appropriately named, in case I find anymore glitches. I'll stop monkeying with that beta code file now.