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Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 2:59 am
by schlomo
Deltaboard is an AVR-based expansion board for the Raspberry Pi computer. The goal of the Deltaboard is to design a highly efficient and flexible interfacing board with a variety of uses. Not only will it breakout digital I/O, SPI, I2C, UART, and analog I/O, but it will also allow you to efficiently power the Pi off of a 2-4 cell LiPo. We imagine three different ways you can use it: as a Raspberry Pi extension board, a standalone Arduino-compatible system, or a low-power data logger. For example, you can set the Deltaboard to make itself and the Pi go to sleep for a certain interval to conserve battery power. (Or, only wake up the Pi when you need the extra computation power.)

A PCB is currently being designed. Here are the main features we expect the finished board to have:


High-efficiency (90+%), low-noise switching regulator
Voltage input: 5-17V into a JST connector
Voltage output: 5V
Step-down linear regulator to 3V3
Based on the ATxmega128A3U microcontroller
8-bit Atmel AVR microcontroller
128Kbytes of Flash memory
12-bit ADC, DAC
RTC
External interrupts on all pins
Highly efficient sleep modes
Runs on 3V3
Compatible with Arduino programming language
Easily fits onto a Raspberry Pi (isn’t forced against any connectors)
About half the size of a Pi board 
Connected to all three communication lines: UART, I2C, and SPI. Able to monitor Linux system, give commands, send sleep requests, etc.
5v external device interface using TI level convertor IC
Onboard USB bootloader
Board firmware can be updated via USB
Also has PDI programming port
Main I/O interface: 28 general I/O pins, 8 power pins
Analog pins over-voltage protected
Digital pins over-current and over-voltage protected
Both 5v and 3V3 power pins
3V3 logic
2 user LEDs, user button, reset button
Mini-USB connector

Here"s a simplified sketch of how the Deltaboard will fit onto the Pi:

Does this sound like a good project? Do you have any suggestions or comments about what we should add, modify, or remove?
EDIT: We will open source all designs once the PCB has been designed. Because most parts will be SMD, I will probably look into getting some assembled, no-soldering-needed versions.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 6:07 am
by hzrnbgy
I also built a GPS add-on for the Pi using an xmega32 but my application is very specialized (a car PC).

Since you have a pretty beefy MCU, how about including a bunch of peripherals on board so users don't need to have flying wires all over the place.

Good additions would be

RTC (the xmega has built in RTC32 by the way)

Hi-capacity SPI flash

maybe a photoresistor, a ds18b20 temp sensor, a humidity sensor, some LEDs

some infrared transmitter LEDs (for remote TV applications)

Xbee port header

a ULN2803 driver for interfacing to higher power peripherals

Just have the SMDs pre-soldered and afford the user to solder their own if they needed the DIP components

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 7:18 am
by Adnan
Va-va-vrooom: Greased Lightning! Something I've always wanted!!

There's no mention, but if you can squeeze in: please break out RasPi's console through a RS232 level translator. It doesn't have to have a clunky DB9 connector (I dislike them anyway), just a micro 3-pin JST will do and let the user decide on the final-mile connector.

It could prove useful for headless console debugging with a laptop whenever Deltaboard is melded with RasPi.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 7:40 am
by Condemned
The following questions are not complaints! It's great to see stuff like this.

Why a mini USB connector?! Surely the whole world is going micro.

Why not use a smaller (cheaper) XMega32A4U? It has 34 I/O lines. Or is there a specific application you're looking at that needs more SRAM / flash?

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 4:11 pm
by schlomo
hzrnbgy said:


Since you have a pretty beefy MCU, how about including a bunch of peripherals on board so users don't need to have flying wires all over the place.

Good additions would be

RTC (the xmega has built in RTC32 by the way)

Hi-capacity SPI flash

maybe a photoresistor, a ds18b20 temp sensor, a humidity sensor, some LEDs

some infrared transmitter LEDs (for remote TV applications)

Xbee port header

a ULN2803 driver for interfacing to higher power peripherals


Those are great ideas. The only problem is that we want to keep the size of the board small and keep the cost as low as possible. Adding a temp sensor, IR transmitter, etc would be nice, but this would start getting expensive, and not all people would want it on the boards. However, to make sure all these devices can be connected easily, the I/O breakout header is designed with abundant power pins.

We plan to use the ATxmega's RTC.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 4:12 pm
by schlomo
Adnan said:


There's no mention, but if you can squeeze in: please break out RasPi's console through a RS232 level translator. It doesn't have to have a clunky DB9 connector (I dislike them anyway), just a micro 3-pin JST will do and let the user decide on the final-mile connector.


We'll definately include an easy way to access the Pi's console from the I/O pin header.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Tue Apr 03, 2012 4:19 pm
by schlomo
Condemned said:


Why a mini USB connector?! Surely the whole world is going micro.

Why not use a smaller (cheaper) XMega32A4U? It has 34 I/O lines. Or is there a specific application you're looking at that needs more SRAM / flash?


I guess--although for the 20 mini USB cables I have in my closet, I only have 1 micro USB. I guess we can go micro if most people prefer that. In any case, it's an easy change to the PCB.

The reason we're using the higher-powered xmega128A3U is because it has 50 I/O pins. To interface with the Pi using UART, SPI, and/or I2C requires 8 pins. In addition, we plan to have 2 level converted I/O pins, 2 user LEDs (and another 2 for power and data, which can be turned off), a user button, and a USB data. So, by the time we add in everything on the board, we have 33 free I/O connections. 28 are being used by the I/O connector. If need be, we can provide access to these extra 4 I/O pins.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Fri Apr 06, 2012 10:55 pm
by LinuxGuru
Any updates for this project? Estimated delivery time and price?

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Fri Apr 06, 2012 11:03 pm
by ringz
Some people have begun moving towards the Atmel ATmega1284p chip because it's the most complex of the arduino compatible chips currently available in a 40 DIP package. Much easier to solder and there is 3rd party support for it in the Arduino 1.0 IDE.

http://www.atmel.com/devices/A.....A1284.aspx

Martyn.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Sat Apr 07, 2012 3:52 am
by schlomo
ringz said:


Some people have begun moving towards the Atmel ATmega1284p chip because it"s the most complex of the arduino compatible chips currently available in a 40 DIP package. Much easier to solder and there is 3rd party support for it in the Arduino 1.0 IDE.

http://www.atmel.com/devices/A.....A1284.aspx


Good idea! I actually originally wanted to use the mega1284P for the Deltaboard for simplicity. But, after some careful consideration, I made the step up to the xmega128A3U because:

-mega1284P doesn't have USB support

-mega1284P only has one SPI port and only 32 I/O lines

So, in order to use the mega1284P with the Pi, you'd have to give up one out of two UARTs and the only SPI port, leaving you with 27 I/O pins with only I2C and UART interfaces.

After a couple days thinking over this, I decided to upgrade to the xmega. Yes, the platform itself is more advanced, but the great thing about AVRs is that most code can be ported over without problem.

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Sat Apr 07, 2012 5:32 pm
by schlomo
LinuxGuru said:


Any updates for this project? Estimated delivery time and price?


We"'re working on it. We"'ve setup a website where we'"ll put status updates and more info: http://deltaboard.org

Re: Deltaboard: a small AVR-based expansion board for the Pi

Posted: Fri Jun 29, 2012 8:30 am
by rasbeer
Just wondering how it's going?