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Old Dec 23, 2010, 10:58 AM
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Originally Posted by Alexinparis View Post
- I2C sensor retrieving time is higher than ADC retrieving time (for coders analogRead() is faster than getting I2C data at 100kHz clock speed)
I think it should be easy to implement interrupt driven I2C functions, so the MCU can perform other tasks when waiting for data on the I2C bus.

I will try to find time to look at it after New Year.

PS: One way to make the new design is to have a mainboard with the MCU and all the sensors on boards, like below, to be soldered in.
http://api.ning.com/files/zF7GvY4aXO....jpg?width=719
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Old Dec 23, 2010, 11:58 AM
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Don't get too excited and got carried away.... As this is the first jump over to next platform.

Keep the Arduino, WMP, integrate Bma 020 and bm085, the rest can comes in later without affect the overall costs at the moment.
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Old Dec 23, 2010, 12:46 PM
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it will be good that we can buy a complet set for less 70usd
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Old Dec 23, 2010, 01:11 PM
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mpu 6000 all in wan or to slo??.
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Old Dec 23, 2010, 06:20 PM
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Question to those familiar with the AVR microcontroller on the Teensy 2++: Just counting the number of digital outputs on the Teensy specs it should be possible to build an Octo (and maybe even have servo control for camera stabilization). Is this correct ? I am not sure as there may be some issues such as some output pins tied to different timers or similar (I believe that Alex had to do some workarounds on the pro mini to enable the additional two outputs for Y6 - because of this timer issue).
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Old Dec 23, 2010, 06:44 PM
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If you guys really want to make a dedicated board, almost every thinker/hacker in the electronics world that can do some boards can also solder SMD's, or use a reflow over/squilet so why not just take the plunge and use an ATmega1280, its even the same used by the old Arduino Mega, and it as 4 16bits timers and 2 8bits ones, this means that it can have 14 pwm channels and the ADC as 16 channels, with those 14 pwm's you can have an octo with 6 servos all driven by hardware, you can also have 4 USARTS so you can add GPS, some Xbee for diagnostics, one dedicated port for PC coms and still have one left.
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Old Dec 24, 2010, 06:35 AM
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Originally Posted by senso View Post
If you guys really want to make a dedicated board, almost every thinker/hacker in the electronics world that can do some boards can also solder SMD's, or use a reflow over/squilet so why not just take the plunge and use an ATmega1280, its even the same used by the old Arduino Mega, and it as 4 16bits timers and 2 8bits ones, this means that it can have 14 pwm channels and the ADC as 16 channels, with those 14 pwm's you can have an octo with 6 servos all driven by hardware, you can also have 4 USARTS so you can add GPS, some Xbee for diagnostics, one dedicated port for PC coms and still have one left.
I'd call that the "Big Solution". Yes, the Mega 1280 is only 15$ - but there are a lot of guys keen on a cheap solution with gyros and accels. And that's where the 328 offers an entry level.

Since you can get a complete ArduinoMega 1280 clone for 30$ shipped I'd start with this one first, adding a sensor board rather than designing a new board from scratch.
http://cgi.ebay.de/Arduino-Mega-Atme...item41557e7571
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Old Dec 24, 2010, 08:32 AM
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I am experimenting with the Arduino Mega 1280 at present however Alex's MultiWiiCopter Sketch will require some adjustments because many of the pins are different than the 328. For example, the I2C on the mega are pins 20 & 21 verse Analog pins 4 & 5 on the 328.
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Old Dec 24, 2010, 08:41 AM
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I would agree that the first point of order should be the design of a sensor shield. This we could probably make happen at a much lower price than Sparkfun brekaouts. I propose a first version with ITG-3200, ADXL345 (or one of the boschs - depending on which works better) and BMP085. It would probably not be a big deal to add pads for a honeywell magneto and Mtek GPS as well.

Having looked closer at uC prices, I think its gonna be hard to come up with something cheaper than a Teensy 2.0++ with AT90USB1286. At least not if we are gonna make them and source the components ourselves...Teensy 2.0++ still has 9 PWM, 8 ADC, 2 16 bit timers and is native USB, so we could free up the serial for Spektrum sat or eventual GPS....Also has more I/O pins than any similar-sized Arduino so it would give more options to play with analog options! And at 27 dollars shipped it is still pretty cheap...and it still fits inside a 50*50 board!

http://www.pjrc.com/teensy/index.html

I still absolutely prefer the 1280USB, but @ 15 dollars a piece I agree that it would probably make for some very expensive boards. As norbert said, Arduino Mega clone could be had for 30 dollars shipped! But I would prefer not having to use that - I think it is too chunky for what it does.....I would prefer to keep it inside a 50*50 mm footprint and try to make it as light as possible.

Anyways... merry christmas to you all!

Best wishes

Jussi
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Old Dec 24, 2010, 09:19 AM
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But if you really want to do this you should make at least 20-25 or more boards to have nice discounts for bulk buys of the various chips, for example one atmega1280 costs 16$ at digikey, but 25 would cost only 10$ each, those 6$ in difference can pay for the pcb's if you use something like seedstudio, or one of the cheap chinese pcb fab houses.
I would like to buy some sensors from Invensense but theirs 53$ to ship anything to Europe is awful expensive, might if someone can arrange a group buy and could ship some chips to Europe it would be great, the Bosch chips have only 10 bits ADC, the ADXL should be better.
As for the boars, yes I understand that the objective is to have a simple working and affordable multi-rotor copter controller, for alot of uses the Mini Pro is still a good choice.
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Old Dec 24, 2010, 10:54 AM
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Hi guys, great thread, and thanks to Norbert for pointing me to it. I enjoyed reading the discussion so far.

I have some ability to produce SMT assemblies--it's an in-home operation so it's small-scale. I'm thinking about making breakouts of some sensors that Sparkfun doesn't sell.

Here's my IMU project, in case anyone is interested. It sounds like it maps into some of what your guys are working on too.

I share some of the same goals as you guys. I'm buiding a UAV/autopilot system and started with the Wii sensors for cost and simplicity reasons. From there I looked at the Sparkfun 9dof and others but decided I could do better with newer components at a lower cost.

I'm working using the Arduino shield format. My main processor is the Fez Panda microcontroller based on the .NET Micro Framework. But that doesn't matter as much in relation to what you guys are doing because the Panda is compatible with Arduino shields.

My goals for this project are:
- Flexibility
- Reconfigurable through software, as much as possible
- The board can be cut down to remove unneeded functionality (Arduino connectors, video display circuitry, radio/servo connections)
- External sensors can be added to the I2C bus (current, pressure, etc.)
- Low cost
- If it can be done through software, do it through software
- Minimal chip count

The core of the board is a Parallax Propeller (8-core) MCU. It handles sensor integration and many other things through software.

The IMU is made up of the Invensense ITG-3200 3-axis gyro, the ADXL345 accelerometer and the HMC5843 compass. These are all I2C components. There's an external I2C bus connector and a connector for a GPS.

There's a header connector on the IMU (separate from the Arduiono headers) that exposes the Propeller serial pins, voltage in/out, UART connectors to the Prop for IMU communications and direct I2C connection to the IMU sensor bus.

The board also has a video overlay circuit (very simple and cheap since Prop does most of the real work) and a set of voltage dividers connected to the Arduino analog inputs to read battery levels, etc.

My plan is to have the Prop handle sensor data integration, PID, GPS stream processing, video overlay, PCM/PWM input and servo output. It has 8 cores which makes in uniquely suited for this task. I think I'd need at least a couple normal MCUs to accomplish these same tasks.

I don't have a total BOM on this handy, the whole deal with the Prop and all the sensors is less than $50. I have a prototype set of PCBs in fabrication right now. I'd love to evolve this into something others can use--it would let me buy in higher volume and get my costs down.

I'd also be happy to work with the community to develop an alternative design, perhaps a scale-down IMU-only version. If they share many of the same components I'd get the same economies of scale.
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Old Dec 24, 2010, 12:03 PM
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Originally Posted by 420RcPilot View Post
... Having looked closer at uC prices, I think its gonna be hard to come up with something cheaper than a Teensy 2.0++ with AT90USB1286. At least not if we are gonna make them and source the components ourselves...Teensy 2.0++ still has 9 PWM, 8 ADC, 2 16 bit timers and is native USB, so we could free up the serial for Spektrum sat or eventual GPS....Also has more I/O pins than any similar-sized Arduino so it would give more options to play with analog options! And at 27 dollars shipped it is still pretty cheap...and it still fits inside a 50*50 board!
Jussi

I am also a big fan of the Teensy line of boards. I've been working on porting Alex's code to the Teensy 2.0++, and have ran into an issue that may prevent using the AT90USB for this project. Alex uses PCINT on PORTD to detect signals from the Rx, but the only pin change interrupts available on the AT90USB are on PORTB. Unfortunately, PORTB is also used for driving 3 of the ESC's, as well as Serial Peripheral Interface (SPI). External Interrupts are available on Teensy's PORTD, but I2C and Serial consume 4 of the 8 pins there.

I haven't quite given up on the Teensy2.0++ (translation: I'm stubborn!), but this limitation has made me reconsider its usefulness in an all-in-one sensor shield.

It's too bad that the 'mega line of boards are physically large, exceeding the 5x5cm limitation. If a board is designed from scratch, I now think the ATmega1280 uC is the better choice.

Happy Holidays to all,
Billy
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Old Dec 24, 2010, 07:36 PM
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Bucharest, Romania
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Building an Arduino Diecimilla compatible shield is the way to go.


Later we could switch betwen various arduino MCU as atmega 1280, but right now the biggest challenge is to make a standard, reliable, cheap, sensor shield.


@cass3825: Why should we keep the board dimensions in 5x5 cm limit and not using an arduino Mega? If you use Mega, you would want a GPS and servos, so the weigth is not critcally important.

As you can see (Andrejc), such imu shield has many other cross-platform applications an woud be a cooperative effort at a larger scale.
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Old Dec 25, 2010, 05:49 AM
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Originally Posted by reverendrichie View Post
I am experimenting with the Arduino Mega 1280 at present however Alex's MultiWiiCopter Sketch will require some adjustments because many of the pins are different than the 328. For example, the I2C on the mega are pins 20 & 21 verse Analog pins 4 & 5 on the 328.
Mariano (mgros) already ported the MultiWii code to the Mega1280 and integrated the code for the BMA020. Maybe you should contact him?
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Old Dec 25, 2010, 05:59 AM
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Originally Posted by andrejk View Post
I don't have a total BOM on this handy, the whole deal with the Prop and all the sensors is less than $50. I have a prototype set of PCBs in fabrication right now. I'd love to evolve this into something others can use--it would let me buy in higher volume and get my costs down.

I'd also be happy to work with the community to develop an alternative design, perhaps a scale-down IMU-only version. If they share many of the same components I'd get the same economies of scale.
Thanks for chiming in, Andrej!

Looks like the next step isn't that far - as soon as we agreed on the form factor and sensors to use. $50 sounds like a good entry!
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