[sdiy] Radio Controlled Synth ?

[Tom Wiltshire]

On 9 Jul 2007, at 14:57, Needham, Alan wrote:

> OK, it's not the quickest responding system on the planet ---
> BUT
> how fast would you wiggle a joystick ?
> how fast is a typical, cheap RC servo ?
> so if it is as crude as nailing a servo onto a pot shaft
> assuming the pulse rate is about 20ms then a microcontroller
> could be as quick as one pulse to update to a new value, 2
> pulses should be plenty. That would be fast enough for most
> joystick applications, pitch bend, filter mod, etc.
> It might be fast enough for an RC theremin pitch control :-|
> 	Alan - now mentally wibbling joysticks

I wasn't wanting to pooh-pooh the idea, just point out the  
limitations. As you say, it'd be fine for most joystick applications,  
and would replace any source of slow control voltages. Slow, complex,  
gently evolving sounds are right up my street, so no problems there.

Personally, I can't stand mechanical solutions, so sticking a servo  
on a pot shaft wouldn't be my preferred method. I'd either:
a) Filter the PWM output directly to derive a control voltage  
proportional to the pulse width
b) Use a uC to measure the pulse width and interface to some other  
type of output

T.


>
>
> -----Original Message-----
> From: Tom Wiltshire [mailto:tom at electricdruid.net]
> Sent: 09 July 2007 11:25 AM
> To: Needham, Alan
> Cc: Scott; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Radio Controlled Synth ?
>
>
>
> On 9 Jul 2007, at 09:58, Needham, Alan wrote:
>
>> Now there's an idea ...
>> the signal to an RC servo is a series of 5v pulses, pulse width
>> modulated for position, it souldn't be too hard to average this
>> to get a crude voltage control signal, a useful signal shouldn't
>> be impossible.
>> 	Alan - lost the plot again!
>
> Yes, I've played with these too. It'd be easy to filter the pulses to
> get a CV output, much like the PWM output on my own EG or LFO
> project. The problem is that the PWM output for RC is at a much lower
> frequency (can't remember of the top of my head, but might be as low
> as 50Hz) so you're going to need a filter with a very low cutoff to
> remove any ripple.
>
> T.
>
>
>
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