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RE: AID: AID and the Orpheus Filter

From: Steven Wood   stevenikoro.com
Date: Sat, 6 Nov 2004 20:38:31 -0800

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Hi Stefan...

Thanks for the thorough response.  I've taken a lenghty absense from
asking questions and spent a lot of time learning electronics, AID, and
the basics of PIC programming.  All of your notes were very helpful in
my understanding the platform.  (I went ahead and built an AID mainboard
PCB using the toner transfer method with great success and will post my
experiences with that when the project is done and I have more time.)

Meanwhile I've done a lot of testing with sensors, motors, and the more
physical aspects of the project, and come up with an overall schematic,
circuits, and pcb layouts.  They are here:

http://ikoro.com/p/orpheusfilter/dev/

There is no code written yet.  I would as much as possible like to
finish the circuits first as they need to go to production soon.

> -----Original Message-----
> From: owner-aid@interaccess.org
> [mailto:owner-aid@interaccess.org] On Behalf Of Stefan Wiechula
> Sent: 15-Oct-04 12:31
> To: AID Mailing List
> Cc: Steven Wood
> Subject: Re: AID: AID and the Orpheus Filter
> 
> 

~snip snip~

> 
> What sort of control do you need over the motors?  If you'd
> like to stop, start and change direction then you'll want an 
> H-bridge circuit such as Rob's motor driver board.  If you 
> want variable speed control, then you'll need to use the PWM 
> outputs from the PIC or some other D/A method.  If you only 
> want to start and stop the motor (not breaking to a stop, 
> just removing power) then you can get away with a single bit 
> digital output per motor.

At first the intention was to go with single bit output, but it has
become evident that PWM is almost a necessity for the application.  I
would like to provide eight channels of (software generated) PWM using
another 16f877 on each perhipheral card.

> It might be possible to run 1 of those motors off the board
> logic power but certainly not 100 to 200 of them!  It's a 
> good idea to isolate such things from the microcontroller as 
> much as possible anyways.  As above, use an H-bridge such as 
> the LS293 or, in the single bit output case, a transistor 
> (someone else can advise you which type).

Right, I have designated a separate PC style power supply for +12V to
all the perhipheral cards, and built them around the ULN2803 Darlington
Array (rated at 500mA per channel).

Direct questions I have now:

[1] If I am supplying +12V to the motors and +5V to the signal circuits
from the same 400W power supply, is it sufficient to decouple them using
capacitors or is there still going to be noise appearing on the signal
lines?  All "ground" is the same anyway, is it not?

[2] What is the maximum length of the AID bus?  Right now the proposed
length is roughly 15-20 meters.  (Crazy?)  I am running only the
channels I require over CAT5 twisted pair.  Is there a particular
pin/wire arrangement that would minimize the amount of interference and
give the best signal?

[3] Is the ULN2803 the right choice for a PWM solution?

[4] Is optoisolation required in addition to the ULN2803 in this
situation?

> Hope that helps,
>
> Stefan.

Very much indeed... Thank you!

Best,
Steve


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