AVR-Chat

I would be greatly appreciate it if anyone 
could share any pointers regarding this subject.
I am investigating if using an avr to control the operation 
of a motor is feasible (on/off only in regular intervals).

At 12:21 PM 10/4/2004, mech_research wrote:



>I would be greatly appreciate it if anyone 
>could share any pointers regarding this subject.
>I am investigating if using an avr to control the operation 
>of a motor is feasible (on/off only in regular intervals).

Certainly, but the AVR will need to work through an appropriate interface.

Thanks for your feedback Robert and Dave

The (very) distant goal is to control an injection molding machine 
using just low cost microcontrollers instead of plc's.
However at this point  just knowing if turning on and off a fan or 
any other low power AC motor is possible and the required components 
to do this, would be a sufficient first step.

--- In AVR-Chat@yahoogroups.com, "mech_research" <mech_research@y...> 
wrote:
> I am investigating if using an avr to control the operation 
> of a motor is feasible (on/off only in regular intervals).

The short answer is that it is feasible.  The longer answer is that 
to do so, you may need one or more devices between the AVR and the 
actual device being controlled.

The AVR outputs, in digital mode, can assume either of two states: 
approximately zero volts and approximately the positive supply 
(typically 5 volts).  Each output can source or sink on the order of 
tens of milliamps (although lower is better because there is a 
combined limit on the current of all outputs).  If the device that 
you want to control meets these specifications and doesn't exhibit 
kickback voltage (as will happen when you switch an inductive load) 
then you can drive it directly.

If your device doesn't meet these specs, you'll need one or more 
interfacing devices (relays, opto-isolators, high-current drivers, 
etc.) arranged so that the one connected to the AVR is compatible 
with its outputs and the one on the opposite end has characteristics 
compatible with your device being controlled.

At 05:21 PM 10/4/04 +0000, you wrote:
>I would be greatly appreciate it if anyone
>could share any pointers regarding this subject.
>I am investigating if using an avr to control the operation
>of a motor is feasible (on/off only in regular intervals).

Do you have a few more details on what you would like to 
drive?  Voltage/current? AC/DC? We could then point you off in the right 
direction.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III

At 08:28 PM 10/4/04 +0000, you wrote:
>Thanks for your feedback Robert and Dave
>
>The (very) distant goal is to control an injection molding machine
>using just low cost microcontrollers instead of plc's.
>However at this point  just knowing if turning on and off a fan or
>any other low power AC motor is possible and the required components
>to do this, would be a sufficient first step.

Your welcome.  Controlling a fan will be a lot simpler than an injection 
molding machine, but certainly a place to start learning.

I'd be tempted to start with Grayhill I/O modules for this.  They are 
isolated which eliminates a lot of worries.  I know they work well at 
isolating the micro from inductive kick back.

Take a look at

http://embrace.grayhill.com/embrace/Item/ASP/PartsList.asp?CatalogGroupID=ACOutput&GroupDisplayLabel=I%2FO+Modules+%5C+Digital+%5C+AC+Output

You will want modules rated for inductive load, something like

http://embrace.grayhill.com/embrace/Item/ASP/Item-Detail.asp?PartNo=70%2DOAC5%2DL&CatalogGroupID=ACOutput&GroupDisplayLabel=I%2FO+Modules+%5C+Digital+%5C+AC+Output

Make sure you check your current and voltage requirements before selecting, 
and give yourself some margin.  Also since this is relatively high (line) 
voltage make sure you have sufficient spacing and that it's fused (and you 
have a manual off switch to isolate everything).

That will get you started w/o having to worry too much about the 
electronics for the power control, leaving you to concentrate on the 
logical control.  I expect the injection molding equipment itself will 
require something a lot more sophisticated than on/off.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III

>
>I'd be tempted to start with Grayhill I/O modules for this.  They are 
>isolated which eliminates a lot of worries.  I know they work well at 
>isolating the micro from inductive kick back.

Exactly what I was going to suggest. :)

I see no reason that you couldn't take an AVR, add some protection/interface circuitry, and use it as an industrial controller.  Take the safety systems outside the controller though. I wouldn't trust that to software.

At 05:49 PM 10/4/04 -0500, you wrote:
>I see no reason that you couldn't take an AVR, add some 
>protection/interface circuitry, and use it as an industrial 
>controller.  Take the safety systems outside the controller though. I 
>wouldn't trust that to software.

Well as long as you don't try to do something like flux vector control 
:).  I agree though keep the hardware interlocks, they are there for a 
reason.  If you want a sobering read sometime read up on the Therac-25 
incidents.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III