Arduino GPS

Just to get my hands dirty and wrap it up with the AVR’s, I created a GPS data logger – using an Arduino board, GPS receiver chip, 4×20 LCD, and a uALFAT microSD board.

A good document on NMEA commands and data formats used by GPS chips is here. Regarding the GPS unit, it was SiRF vs Trimble, and I went for SiRF, the SiRF III (the EM-406A by USGlobalSat). I picked it over the Trimble Lassen IQ and the Parallax.

Of course you can buy a GPS data logger board with LCD for about $200. But the whole point is that it’d be a learning exercise, an interesting one :-).

I decided to write it in raw C (UART driver, LCD driver, flash data logger,…) instead of Arduino’s Wiring language. This amounts to pretty much reading most of the 300 page data sheet for the MCU, giving you a thorough understanding of all aspects of the MCU – GPIO, clocks, counters, interrupts, UART, SPI, I2C,… all related considerations like registers, masks, timings, memory organization,…

(photo updated, 12/2007).

Arduino LCD

Interfaced a 4×20 character LCD panel to the Arduino. Details on interfacing any Hitachi HD44780 based LCD panel can be found here.

I went for the default parallel LCD’s. They’re cheap, about $15 for a 20×4 panel on eBay (HD44780). The serial ones cost about 2-3 more. These LCD panels allow you to use 4 data lines (with some bit-banging) instead of 8. Get one that is STN and transflective (vs reflective and transmissive), known for better contrast and brighter.

Check out also LCDProc.

The Arduino

Just got it today :-) More than anything, the Arduino is a great learning platform for anyone interested in the embedded world. The entire platform is open (hardware schematics, bootloader, lots of examples, etc.).

Arduino comes with a nice language that abstracts out lot of the bit-level stuff. But for learning purposes I’d recommend just using C – i.e. to get right down to the metal to get to know the AVR. Ubuntu has a nice ready-made GNU C toolchain for the AVR which works quiet well. There is also an Eclipse plugin. You’ll probably end up reading two-thirds of the 350 page ATmega168 specs… but very worthwhile. Once you’ve done one, you’re all set to handle any 8-bit MCU. I found Atmel’s AVR docs are very well done, complete with assembly language and bit-level C-language code snippets.

Also, check this site out: Atmel AVR Application Notes. Tons of stuff. You don’t really need to buy any embedded systems books. The stuff here plus the Atmel AVR 8-bit Instruction Set set document should be all that you need.

ATmega128

The Atmel ATmega128 AVR is a nice little full featured 8-bit MCU. It is as good as it gets among general purpose MCU’s (i.e. not including MCU’s which add on a host of other features like controllers for LCD, USB, Ethernet MAC, DSP, MMU, etc.).

For my own quick reference:

Feature	ATmega128	ATmega168	ATmega8
Flash	128K	16K	8K
SRAM	4K	1K	512
EEPROM	4K	1K	512
UART	2	1	1
8-bit Timer	2	2	2
16-bit Timer	2	1	1
PWM (channels)	6+2	5	3
10-bit A/D (channels)	8	6	8
DebugWire/OCD	Y	-	-
Analog	-	Y	-
JTAG	Y	-	-
SPI	1	1	1
TWI	1	1	1