Post by thread:[PIC]: Projector Lift

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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}> 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 > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

In this case, I'd use limit switches rather than a stepper. Bob Ammerman RAm Systems ----- Original Message ----- From: "Matt Johnson" <spam_OUTmattTakeThisOuTALTAPACIFIC.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Saturday, September 21, 2002 11:37 AM Subject: [PIC]: Projector Lift {Quote hidden}> 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 > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> 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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

"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. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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. :) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

"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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> > 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 -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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}> > 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 > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> 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 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 ___________________________________________ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

>-----Original Message----- >From: Matt Johnson [.....mattKILLspam.....ALTAPACIFIC.COM] >Sent: Saturday, September 21, 2002 1:58 PM >To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.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 -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu