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Author Topic: [50$ robot] Modyfying servos with atmega88  (Read 1436 times)

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Offline SidorTopic starter

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[50$ robot] Modyfying servos with atmega88
« on: December 08, 2010, 08:54:25 AM »
I just started doing my first robot (as [$50 robot] indicates).
Unfortunately due to inaccessibility reasons I bought atmega88 instead of atmega8.
No I finished my circuit, and moved on to modifying servos step (http://www.societyofrobots.com/actuators_modifyservo.shtml).
I downloaded .hex file to my atmega88, and put it back to circuit (I didn't add the programmer header socket to my circuit, I'm using external programmer), and put the power on (with one servo attached to the circuit) and nothing happened :(
Then I checked my entire circuit in terms of connections and voltage (with microprocessor unplugged) and it seems OK.
The only logical conclusion to me is that I screwed microprocessor programming step.

So do i have to recompile hold_servo so that it will be ok on atmega88? and if yes where can i find the source code (or at least what code should I write, using the abstraction provided in Photovore v1.zip (from step 4 $50))?

Finally sorry for my bad English and thank you in advance for help :)

Offline SidorTopic starter

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Re: [50$ robot] Modyfying servos with atmega88
« Reply #1 on: December 14, 2010, 08:29:41 AM »
Oh, come on, I'm sure it is not hard question for smb who already done some microcontroller programming...

Offline robots-in-brighton

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Re: [50$ robot] Modyfying servos with atmega88
« Reply #2 on: December 14, 2010, 10:37:36 AM »
From the description, the code referred to (compiled to hold_servo.hex) sends a constant 1.5 ms PWM signal to a selected pin to centre the servo attached to that pin.

I'm not sure why the source for this utility has not been published. However, it may be possible to disassemble (decompile) the .hex file back into an editable format using applications from the AVR toolset and you could then make any modifications required to reflect the change in hardware. Having done this, you may also have to modify the main photovore source in a similar fashion.

This appnote describes the issues of upgrading from atmega8 to atmega88: http://www.atmel.com/dyn/resources/prod_documents/doc2553.pdf. The document states "...ATmega88 is not designed to be a replacement for ATmega8, but is pin compatible and has a very similar feature set..." so this may be a simple task or it may require more experience.

In fairness to the community here, the project is a step-by-step detailed description of building a robot using a particular device, and you chose a different one. I would review that decision if you wish to continue with the $50 robot.


 


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