[PD] arduino-help.me.please.pd [gadlletas]

Martin Peach martinrp at alcor.concordia.ca
Mon May 29 18:47:32 CEST 2006

Martin Peach wrote:
> Christian Klippel wrote:
>> hello,
>> servo's are _slightly_ different in that they dont take the classical 
>> pwm that you can regulate from 0..100%.
>> instead, a servo needs a repetetive pulse between 1 and 2 miliseconds.
>> that pulse train can have a frequency from 30 to 400 hz, for example, 
>> but the pulse width stays in the same range. a pulse of 1.5 ms 
>> positions the servo into the center, 1 and 2 ms are for the full 
>> movement to the left or right respectively.
>> in the controller you need a loop (or, preferably, an interrupt) that 
>> just waits some 20 ms, then sets the pulse on, waits 1 to 2 ms, and 
>> turns off again, then repeat ....
> ...or a 50Hz pwm with a positive pulse width varying between 5 and 10 
> percent. Doing this from a soundcard output is bad because 50Hz is close 
> to the low-frequency cutoff of the card, so the parts of the pulse that 
> should be at either 0V or 5V will actually drift towards each other. You 
> would need to add a comparator to get a digital level signal.
> The arduino digitalWrite command in conjunction with delayMicroseconds 
> (for the positive pulse)and delay (for the negative pulse) should be OK 
> for this.

Oh yes, and the arduino analogWrite (pwm) will not work because it 
splits the pwm signal into many small pulses so that it works better for 


> Martin
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