[PD] pd/arduino pwm > servo motor
hans at eds.org
Tue Oct 24 06:56:39 CEST 2006
On Oct 21, 2006, at 6:49 PM, Martin Peach wrote:
> Hans-Christoph Steiner wrote:
>> On Oct 20, 2006, at 4:31 PM, <martin.peach at sympatico.ca>
>> <martin.peach at sympatico.ca> wrote:
>>> "David NG McCallum" <d at mentalfloss.ca> said:
>>>> I can see that if you tried software PWM through pins 9-11 it
>>>> be any different than using any of the other digital pins. But I
>>>> thought that pins 9-11 did hardware PWM through the analogWrite()
>>>> function in the regular Arduino C. Am I wrong on this?
>>> I don't know. I don't have an Arduino, I'm trying to make
>>> something with a PIC that emulates the Arduino running Firmata.
>>>> Do you mean that hardware PWM on those pins hasn't yet been
>>>> implemented with Firmata?
>>> That's what I meant. Also that software PWM has not been
>>> implemented with Firmata either AFAIK.
>> Hardware PWM is implemented and functional on the lastest firmata/
>> pduino release. Software PWM and pulseOut are still lacking.
>> Once one/both of those are implemented, servo control will be
>> possible. Any volunteers?
> Ah I see, the hardware PWM function is called analogWrite in Wiring.
> My calculations based on a 16MHz arduino clock and the arduino
> firmware at :
> suggest that the hardware pwm is running at 490Hz.
> Anyone know if this is the case?
> If so, this should work for DC motors but is too fast for servos
> and too slow for audio.
The Atmel ATMEGA8 has a 30kHz hardware PWM, so it'll do audio too.
But yes, its waaaay too fast for servos.
> It could be used as an 8-bit DAC if a lowpass filter is placed on
> the output, something like a 10k resistor feeding a 0.1uF capacitor:
> 10k |
> = 0.1uF
> As for software PWM it would work best if you had access to the
> timer interrupts, which would have to occur at the granularity of
> the pwm (for servos, 1/256 ms ~ 4us). I can see how to do it by
> directly writing assembly code but in the context of the Wiring
> environment I'm not sure...
There are timer interrupts available. They are not documented in the
Wiring stuff, but the Wiring code is literally just C++, so you can
use the standard calls. I haven't touched that yet though...
The arc of history bends towards justice. - Dr. Martin Luther
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