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'[PIC]: Projector Lift'
2002\09\21@120544 by Matt Johnson

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I am wondering if anyone has some good sample code for an IR Decoder. I am
building a ceiling projector mount that lowers from the ceiling via an
electrical motor. I would like to control the projector mount with my
remote control.

Also, what is the best way to get an electric motor to spin for just a
certain number of times and then stop? I want to be able to raise and
lower the mount via a corkscrew action but need precision clockwise and
counter clockwise movement. Is this best done with a stepper?

- Matt

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2002\09\21@133547 by Peter L. Peres

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Gear the motor down and use a rev counter (you do not need an encoder
probably), and a precise end switch at one end. Both could be optical
interrupters. The code depends on what remote protocol you have. There are
several remote receiver projects on the web.

Peter

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2002\09\21@141550 by Matt Johnson

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Can you gear me towards a project for a universal remote that is specific
to the PIC or AVR? I have not been able to find one!

- Matt

On Sat, 21 Sep 2002, Peter L. Peres wrote:

{Quote hidden}

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2002\09\21@142426 by Brandon Fosdick

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Matt Johnson wrote:
> Also, what is the best way to get an electric motor to spin for just a
> certain number of times and then stop? I want to be able to raise and
> lower the mount via a corkscrew action but need precision clockwise and
> counter clockwise movement. Is this best done with a stepper?

Don't know about the IR part. Have you thought about using contact switches on
the screws or the platform? Setup one switch to trigger when the platform is all
the way up and another to trigger when its down. Then use a PIC to turn the
motor on/off when the switches trigger.

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2002\09\21@144610 by Bob Ammerman

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In this case, I'd use limit switches rather than a stepper.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Matt Johnson" <spam_OUTmattTakeThisOuTspamALTAPACIFIC.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Saturday, September 21, 2002 11:37 AM
Subject: [PIC]: Projector Lift


{Quote hidden}

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2002\09\21@145835 by Bob Ammerman

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> Don't know about the IR part. Have you thought about using contact
switches on
> the screws or the platform? Setup one switch to trigger when the platform
is all
> the way up and another to trigger when its down. Then use a PIC to turn
the
> motor on/off when the switches trigger.

Even better. Wire the switches up so that when the motor is at the
corresponding extreme of motion the power to the motor is disconnected by
the switch itself. This way, if your PIC crashed you won't run the motor
into the stops.

You can use a DPDT relay wired up as a reversing switch and connect two
diodes across the normally closed switch contacts to do the job, like this:

[Use fixed font for ascii art below!]

              NC
      DPDT    Upper
      Relay        Limit
      wired as a   Switch
             reversing   +--|/|--+
POS       switch      |   |
MOTOR         +----+      |       |
POWER --------|    |------+--|>|--+---------->
             |    |
MOTOR         |    |    To motor
POWER --------|    |------+--|>|--+---------->
NEG           +----+      |       |
                         |       |
                         |       |
                         +--|/|--+
      NC
     Lower
                          Limit
                          Switch

Bob Ammerman
RAm Systems

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2002\09\21@150523 by Peter L. Peres

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On Sat, 21 Sep 2002, Brandon Fosdick wrote:

*>Matt Johnson wrote:
*>> Also, what is the best way to get an electric motor to spin for just a
*>> certain number of times and then stop? I want to be able to raise and
*>> lower the mount via a corkscrew action but need precision clockwise and
*>> counter clockwise movement. Is this best done with a stepper?
*>
*>Don't know about the IR part. Have you thought about using contact switches on
*>the screws or the platform? Setup one switch to trigger when the platform is all
*>the way up and another to trigger when its down. Then use a PIC to turn the
*>motor on/off when the switches trigger.

Imho this is not accurate enough. The projector must be pointed
accurately. The switches will have too much hysteresis for this.

Peter

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2002\09\21@150726 by Peter L. Peres

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On Sat, 21 Sep 2002, Matt Johnson wrote:

*>Can you gear me towards a project for a universal remote that is specific
*>to the PIC or AVR? I have not been able to find one!

http://www.google.com/search?hl=en&ie=ISO-8859-1&q=ir+remote+receiver+code+pic

Peter

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2002\09\21@152404 by Brandon Fosdick

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"Peter L. Peres" wrote:
> Imho this is not accurate enough. The projector must be pointed
> accurately. The switches will have too much hysteresis for this.

Hadn't thought of that. Although, if the switches trigger before a physical
travel limit the PIC should be able to compensate by reversing the motor for a
calibrated length of time. Or if the switches trigger before the desired end
point the PIC turns the motor off after a calibrated delay.

How precise does this need to be? I'm thinking the error shouldn't be more than
a few millimeters if the motors are slow compared to the switches and the PIC.

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2002\09\21@153105 by Brandon Fosdick

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Bob Ammerman wrote:
> Even better. Wire the switches up so that when the motor is at the
> corresponding extreme of motion the power to the motor is disconnected by
> the switch itself. This way, if your PIC crashed you won't run the motor
> into the stops.
>
> You can use a DPDT relay wired up as a reversing switch and connect two
> diodes across the normally closed switch contacts to do the job, like this:

Thats too easy. :)

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2002\09\21@154028 by Robert Rolf

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"Peter L. Peres" wrote:
> On Sat, 21 Sep 2002, Brandon Fosdick wrote:
> *>Matt Johnson wrote:
> *>> Also, what is the best way to get an electric motor to spin for just a
> *>> certain number of times and then stop? I want to be able to raise and
> *>> lower the mount via a corkscrew action but need precision clockwise and
> *>> counter clockwise movement. Is this best done with a stepper?
> *>
> *>Don't know about the IR part. Have you thought about using contact switches on
> *>the screws or the platform? Setup one switch to trigger when the platform is all
> *>the way up and another to trigger when its down. Then use a PIC to turn the
> *>motor on/off when the switches trigger.
>
> Imho this is not accurate enough. The projector must be pointed
> accurately. The switches will have too much hysteresis for this.

No they don't, since you'll be operating them from the same direction
when you use them to sense the endpoint. Any good snap action switch
(Micoswitch, Alco, C&K) will give you a very reproducible endpoint.

Also, if you short out the DC motor when the limit is hit you greatly
reduce coasting since the motor stops nearly instantly.
Satellite jack arms use this technique (or more precisely, the receiver
does) and I have found reproducibility in the sub mm range on a 60cm
Von Weis arm running with no load.

You might also consider using a fixed stop for the projector and
letting the lift overshoot. E.G. Have the projector hanging on
the lift hook, but at full extension the projector rests on a
flange/base which the hook drops past. That way your final position
is NOT dependent on the motor rev. count and simple limit switches will
suffice. If your base endpoint has a pyramid shape, it will be self aligning.

And steppers will not have as much torque as a good DC motor,
and are much harder to drive (more electronics).

KISS (keep it simple stupid). IOW, a turns counting PIC is probably
overkill.

Robert

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2002\09\21@160745 by Wouter van Ooijen

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> > Imho this is not accurate enough. The projector must be pointed
> > accurately. The switches will have too much hysteresis for this.

Use an 'opto interruptor' (is that the right name?) accurate enough for
positioning the head in floppies...

Wouter van Ooijen

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2002\09\21@180546 by Peter L. Peres

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On Sat, 21 Sep 2002, Brandon Fosdick wrote:

*>How precise does this need to be? I'm thinking the error shouldn't be more than
*>a few millimeters if the motors are slow compared to the switches and the PIC.

Depending on how the mechanics are set up and how far and how big the
screen is one milimeter may be a lot. I have some experience in this,
believe me. I'd even go as far as to suggest a software-settable 'down'
stop. Fiddling with tall ladders in a semi-darkened place full of chairs
and/or tables that cannot be moved comes to my mind as a very good reason,
from my past experiences.

Peter

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2002\09\21@180748 by Peter L. Peres

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On Sat, 21 Sep 2002, Brandon Fosdick wrote:

*>Bob Ammerman wrote:
*>> Even better. Wire the switches up so that when the motor is at the
*>> corresponding extreme of motion the power to the motor is disconnected by
*>> the switch itself. This way, if your PIC crashed you won't run the motor
*>> into the stops.
*>>
*>> You can use a DPDT relay wired up as a reversing switch and connect two
*>> diodes across the normally closed switch contacts to do the job, like this:
*>
*>Thats too easy. :)

Moreover you can wire the relay to one of those 'power buddy' devices and
have it pull in when the projector lamp comes on, so you need just one
control, for the projector. But invest in precise 'down' settings. See my
other postings.  There are mechanical ways to achieve this (hard stop +
spring or slip clutch on mechanism for ex.).

Peter

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2002\09\21@181617 by Peter L. Peres

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On Sat, 21 Sep 2002, Robert Rolf wrote:

*>> Imho this is not accurate enough. The projector must be pointed
*>> accurately. The switches will have too much hysteresis for this.
*>
*>No they don't, since you'll be operating them from the same direction
*>when you use them to sense the endpoint. Any good snap action switch
*>(Micoswitch, Alco, C&K) will give you a very reproducible endpoint.

True but I have bad experiences with 'homemade' (actually small shop
built) gear.

*>Also, if you short out the DC motor when the limit is hit you greatly
*>reduce coasting since the motor stops nearly instantly.
*>Satellite jack arms use this technique (or more precisely, the receiver
*>does) and I have found reproducibility in the sub mm range on a 60cm
*>Von Weis arm running with no load.

This is pretty good. But it probably runs very slowly to start with. The
projector should come out and get in with about 10cm/sec (0.3fps) unless
it's very huge.

*>You might also consider using a fixed stop for the projector and
*>letting the lift overshoot. E.G. Have the projector hanging on
*>the lift hook, but at full extension the projector rests on a
*>flange/base which the hook drops past. That way your final position
*>is NOT dependent on the motor rev. count and simple limit switches will
*>suffice. If your base endpoint has a pyramid shape, it will be self aligning.
*>
*>KISS (keep it simple stupid). IOW, a turns counting PIC is probably
*>overkill.

Only if you do not combine the vertical alignment into the final down
position, and make it adjustable. Acoustic ceilings have a way to give and
sometimes the screen must be moved up or down.

Peter

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2002\09\21@182250 by Matt Johnson

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One idea that I liked that doesnt require mechanical switches is using
something to check when the current spikes (which would be because it hit
a stop and using the current spike as an indicator of when to stop. Then I
dont have to worry about mechanical switches. Does anyone have a schematic
or code on how to check for the current spikes?

- Matt

On Sat, 21 Sep 2002, Bob Ammerman wrote:

{Quote hidden}

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2002\09\21@190430 by Olin Lathrop

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> Also, what is the best way to get an electric motor to spin for just a
> certain number of times and then stop? I want to be able to raise and
> lower the mount via a corkscrew action but need precision clockwise and
> counter clockwise movement. Is this best done with a stepper?

I think limit switches would be easier.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\09\21@191057 by David Duffy

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Peter wrote:
>On Sat, 21 Sep 2002, Brandon Fosdick wrote:
>
>*>Matt Johnson wrote:
>*>> Also, what is the best way to get an electric motor to spin for just a
>*>> certain number of times and then stop? I want to be able to raise and
>*>> lower the mount via a corkscrew action but need precision clockwise and
>*>> counter clockwise movement. Is this best done with a stepper?
>*>
>*>Don't know about the IR part. Have you thought about using contact
>switches on
>*>the screws or the platform? Setup one switch to trigger when the
>platform is all
>*>the way up and another to trigger when its down. Then use a PIC to turn the
>*>motor on/off when the switches trigger.
>
>Imho this is not accurate enough. The projector must be pointed
>accurately. The switches will have too much hysteresis for this.

I've done this recently. I used opto's for to tell the PIC where to stop
but also had
mechanical limit switches just outside the normal desired stop positions in
case
the PIC ever locked up or one the TRIACs went short. (3 wire 240Vac motor)
I may be paranoid but the motor concerned opens a large cabinet so has quite a
bit of grunt and would damage the cabinet gear system if allowed to run amok!
David...
___________________________________________
David Duffy Audio Visual Devices P/L
U8, 9-11 Trade St, Cleveland 4163 Australia
Ph: +61 7 38210362 Fax: +61 7 38210281
New Web: http://www.audiovisualdevices.com.au
___________________________________________

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2002\09\21@194243 by jpeixoto

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Just an idea... Ever looked at a satellite dish positioner ???

It does exactly what was mentioned earlier: has a rotation sensor (reed
switch) and mechanical limiter switches.


{Original Message removed}

2002\09\21@234814 by Ray Gallant

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source=If you're talking about an AC motor, you could select a split capacitor (bi-direction AC motor).  You can write your PID routines accordingly if you feel like it.  I am using that type now in an agitator application with a gear ratio included that give me 6 PRS (115VAC, 1/6A).  Mechanical stops should take care of failures.  If your concern, you can always put a thermal circuit breaker on the AC Motor line.
On the other hand, a synchronous motor or encoder type is not that difficult to handle.  The encoder can also (fixed) be an external magnetic strip being read by a coil pickup or other device.  The steps in the mag strip are very fine.  Sound like a nice project.

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2002\09\22@130632 by Nelson Hochberg

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Back in 1970, I was teaching and I helped two of my students to do exactly
this except we didn't have video projectors or IR remotes back then.  The
projector lift moved a platform up and down that held a slide projector, a
movie projector and a film strip projector.  With a dpdt hard wired switch
at the podium (wired exactly as Bob Ammerman described), the lift lowered
two feet from the ceiling.  We had a push button that shorted out the down
micro switch that lowered the table two more feet to the stops so we could
thread the movie/strip projectors or change the slides.

All parts were obtained from a local (but well stocked hardware store). Four
sprockets clamped to nuts threaded onto four all thread bars were connected
via a bicycle chain to the motor.  The four all thread bars were bolted via
pipe floor flanges to a plywood shelf.

If I were to lift just one projector today, I would buy a surplus linear
actuator for the mechanical portion.  It would have the motor, non-turning
screw, adjustable stops all rolled into one part.

Here is a circuit that will receive the IR signal:
http://www.aaroncake.net/circuits/irremote.htm
Adjust R6 until the relay clicks with your remote control transmitter.  This
would actuate with any button on the remote control.  If you want to actuate
on a specific button on the remote, you will need to decode the modulated
signal with an oscilloscope and route pin 8 of IC2 to a PIC.

If you know the carrier frequency of the remote (you can determine that with
an oscilloscope also), you can use the appropriate photo module fed into the
PIC.  One of the Vishay devices in the following link or equivalent:
http://www.vishay.com/document/82058/82058.pdf

Hope this helps.

Nelson

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2002\09\23@090535 by Hazelwood Lyle

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>-----Original Message-----
>From: Matt Johnson [.....mattKILLspamspam.....ALTAPACIFIC.COM]
>Sent: Saturday, September 21, 2002 1:58 PM
>To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
>Subject: Re: [PIC]: Projector Lift
>
>
>Can you gear me towards a project for a universal remote that is
specific
>to the PIC or AVR? I have not been able to find one!
>
>- Matt


Matt,
I have had good success using the PIC IR decoder from
Terry Weeder. This was from an article in the Feb. 1998
issue of "Nuts & Volts". It uses a 16C54 along with an
external EEPROM. You can get order a back issue from
http://www.nutsvolts.com, and the software is at their ftp
site: ftp://nutsvolts.com/irremote.zip

This project can be programmed to any 38-40 khz remote
control that you like, and can be re-programmed easily.

There is also a version that has been ported to C and
should be more "portable" (if you have a C compiler).
You can find info on this at http://www.zianet.com/tdl/download.htm

I have not tried this "updated" version.

Good Luck,
Lyle

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