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Old Jun 03, 2011, 04:17 PM
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OlliW
Joined Sep 2009
2,925 Posts
GA250 Hardware

GA250 Hardware:
In the following pictures are shown the top and bottom sides of the print board contained in the GA250 together with my labeling of the components, the electric circuit diagram, and the original fuse settings:


http://www.olliw.eu/uploads/gyro-GA250-withanno-wp.jpg


http://www.olliw.eu/uploads/gyro-GA250-circuit.png

Fuse Settings: http://www.olliw.eu/uploads/gyro-GA2...ogfuses-wp.jpg

The hardware consists of an Atmel Atmega8 micro controller (the label has been made irrecognizable, but according to avrdude the chip ID is 0x1e9307) run by a 8 MHz ceramic oscillator. The gyro sensor is the Invensense ISZ-650 (the label has also been made irrecognizable, it also could be the ISZ-500, but this appears unlikely). The GA250 offers a red and a blue led for signaling. Also, it offers a quite elaborate voltage source and reference voltage circuitry, and the print board (4 layer!) and fabrictaion (soldering!) appears to be of high quality. I would not have expected to see such a high quality both as regards the electronic scheme and fabrication in such a low-cost product (I hope that this is not going to change in time). Congrats ASSAN. The most beautiful thing, however, is that the ISP pins, which allow programming the micro controller, are easily available via soldering pads. Besides the fact that it offers a high quality MEMS gyro sensor, this point makes the GA250 an ideal platform for this project. Hardware-wise it can't be simpler.

Atmega8 datasheet: http://www.atmel.com/dyn/products/pr...0&part_id=2004
ISZ-650 datasheet: http://invensense.com/mems/catalog.html

The ports of the Atmega8 are connected as follows:
PB0 / ICP: input signal 1 from reciever (rudder input in the gyromixer)
PD2 / INT0: input signal 2 from reciever (throttle input in the gyromixer)
PB2 / OC1B: output signal 1 (PPM output signal for motor B in the gyromixer)
PC0 / ADC0: PTATS signal from ISZ-650 gyro sensor (this reads the temperature, not used in the gyromixer)
if one removes R14 this port may also be used as a further analog input, e.g. for a lipo saver
PC1 / ADC1: Zx4.5 out signal from ISZ-650 gyro sensor (+-440/s -> +-1V gyro signal)
PB4 / MISO: AZ pin of the ISZ-650 gyro sensor (allows to zero the gyro signal)
PD3: red LED
PD4: blue LED

Via the ISP pads additionally the following ports are easily available:
PB3 / MOSI: general port (PPM output signal for motor A in the gyromixer)
PB5 / SCK: general port (connection to the programming box and bootloader in the gyromixer)

Two further ports are available through careful soldering (and removing of R11):
PD5: (not used yet in the gyromixer)
PD0/PD1: these two ports are connected (not used yet in the gyromixer)

In order to use the GA250 for our purposes, in principle only two cables need to be soldered to those two pads, which are connected to ports PB3 and PB5. These together with the other cables will provide the two PPM inputs for rudder and throttle, the two PPM outputs for the BESCs of motor A and B, and an additional connector for attaching the programer box.
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