[PD] comport and servos

[Martin Peach]

Martin Peach wrote:
> Martin Peach wrote:
>>
>> To control a servo, using 1200 baud, the numbers 0, 128, 192 and 224, 
>> 240 should position the servo roughly at 1/5 range steps. 240, 248, 
>> 252, 254 and 255 may be too short. 
>
> That should be 4800 baud for 9 bits of 1/4800 seconds giving 1.875ms 
> for the widest pulse. 4500 baud would give a 2ms pulse. Currently 
> [comport] doesn't accept arbitrary baud rates even though they should 
> be possible on modern hardware. I'll try it and see...
> (Adding messages to control the RTS and DTR lines worked OK in linux, 
> but screws up data transmission, data is sent at unpredictable times. 
> Probably needs to be flushed. I still need to implement the Windows 
> version of this. )
>
Today I put a new version of [comport] and comport-help.pd in cvs at 
http://pure-data.cvs.sourceforge.net/pure-data/externals/iem/comport/comport/
Now you can set dtr and rts lines to control things, also read the dsr 
and cts lines. This doesn't interfere with serial data transmission 
unless cts/rts or dsr/dtr flow control is enabled as well. Here it works 
in winXP and linux at least.
As far as servos go, jitter is worse using the control lines: while the 
start of a pulse can be fairly accurately timed (using metro) to ~0.3ms, 
the end occurs at x ms or x+5ms regardless of the audio latency.
It should work for switching on a coffee maker or a light though, just 
connect dtr or rts to a solid state relay.
I suppose a [comport~] object could use a signal inlet for some kind of 
trigger to send a message that was set up on another inlet...any 
suggestions?

Martin