Looking for the name on a concept AKA Do "reverse data loggers" exist?

Hello all,
I am a chemical researcher looking to find out what the heck is the name of a piece of equipment.
I work all the time with data loggers, some of which are very small
and reasonably priced. $50 for four channels logging of incoming voltage, saved to a file that can then be downloaded. What would you call something that did the reverse, that is send out voltages based on an uploaded file? Assuming I a looking for the cheapest possible incarnation, what would the likley cost be?
I am thinking about building a small robot but since any change is command steps will be rare I dont want more computer than is necessary.
Ghostwriter
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ghostwriter wrote:

I don't know that there is a specific name for this type of device other than a generic "data playback," but it's generally used in such things as animatronics, machine training, and QC testing. You might try companies that specialize in these applications.
If you want to roll your own, a basic microcontroller would be all that's necessary. You might find software already written for the microcontroller of your choice, or you could write your own. You basically need to run a clock -- all microcontrollers have at least one -- and compare the clock times with the recorded changes in EEPROM, RAM, ROM, or Flash.
Most low-cost microcontrollers do not have analog outputs, but making one isn't difficult. Probably the easiest is to use a separate DAC chip. There are several that are multi-channel -- 11 or 12 lines of your microcontroller will provide (as an example) 8 bits (256 steps) for the voltage, and 3 or 4 bits for addressing which analog output you want to apply the voltage to. There are 10, 12, and 16 bit DACs available as well.
If you create your own solution I'd say the parts would be in the $20-50 range, depending on the number of output lines and other features.
-- Gordon
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wrote:

Aren't there serial DACs. So you could serial out to the DAC instead of using a bunch of I/O lines in parallel. I have an ADC that has a serial out.
Joe McKibben
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Joe McKibben wrote:

Sure, all kinds. But MCUs with a several 8-bit wide ports are common and inexpensive these days, so that shouldn't be the deciding factor. It's a bit more coding and overhead to bit-bang out or use SPI or I2C or whatever, but it's a good approach as well. I'd probably use serial myself because I don't like wires!
-- Gordon
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I Googled on "animatronics" and ran across this site: http://www.animatronics.org / Its worth a look for the Black Magic Woman animatronic video if nothing else ! The other links might provide some info to give you some other ideas ...
Good luck ! JCD
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pogo wrote:

It's pretty good. The lips are the interesting thing.
Of course, Carlon Santana doesn't sing the song, and he's right-handed. <g> The following video does the group, and Santana justice:

http://www.youtube.com/watch?v=y_b3LMoQUJ0

-- Gordon
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Gordon McComb wrote:

Ooops... Carlos
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Yeah - I agree - the lips are in perfect sync. And I doubt any animatronic whatsitz will EVER be able to tease a guitar like Carlos Santana! Dang! Now I want to go to a concert!
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pogo wrote:

It's the lips that really make this animatronic, yet the site is virtually devoid of any discussion how the designer/programmer achieved the sync and lip shapes. Might be a trade secret. Oh, well.
I guess the fact that it is one of the most famous guitar riffs in modern rock, coupled with a very rudimentary animation with the skeletal hands, that made me look for more. I might have had a different reaction if the animatron was strumming a ukulele and singing kumbayyah!
-- Gordon
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That would be something involving a D/A (Digital to Analog) converter(s). Your data logger would have used an A/D (Analog to Digital) converter, along with some other electronics to store the data as a file.

Does the robot have a specific purpose ? Or are you simply trying to get started in the hobby by building one based on concepts & devices that you are familiar with ? I ask this because the statement "any change is command steps will be rare" sounds like you have a very specific purpose in mind.
Without knowing more, I would *guess* that you need to look into something like a small programmable microcontroller that offers one or more D/A converters onboard, such as the Basic Stamp from Parallax, the Oopic, PIC AVR, etc. Prices range from around $50 on up depending on what you need, what gear you already have, etc.
Tell us more and I'm sure we can provide more specific suggestions for you. JCD

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I am working on an open source project
www.reprap.org
I have been primarily working as a chemistry specialist, but had the idea of replacing the computer with a calibrated command set stored in a small amount of memory. I estimated that would allow you to put $100 or so into each machine and then run them off of a single computer. Since the current build rates are very slow there really isnt much need to change the command set more often than once a day, or even less if you dedicate specific machines to the construction of a small range of parts. I was also thinking that would simplify troubleshooting of the system since you could standarize a set of "shake-down" tests and graph signal vs response.
Ghostwriter
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Hmmm ... This puts a different spin on it - at least for me - than what I was originally thinking you needed. But the project is certainly cool!
Not the answer to your questions, I realize, but my first concern from browsing the reprap catalog site at http://reprap.org/bin/view/Main/HDPE is how well does the HDPE plastic stick to itself during the deposition of the various layers ? I know for a fact that a couple of people that frequent this group can make some very learned & intelligent comments on that subject, for sure.
Getting back to your original question, if the build cycle is really fairly slow, and depending on how fast the plastic (or other extrusion material) comes out - you may be able to get away with just serially commanding each motor/actuator from the main computer. Another approach would be to use the main computer to download an entire program (small, that is) complete with coordinates stored as code data, and then trigger each motor controller at the appropriate time from the main computer (using the main computer as an executive) .
Hope that makes sense. jcd
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That really depends on how hot you can get the material before it hits the air and also on hot heavy of a bead of material you are extruding. The problem is that the hotter/larger beads tend to sag so you have balance the interlayer adhesion versus part deformation. Currently some of the machines have produced watertight vessels using HDPE. Its traditional for the first "real" test of an extruder be the creation of a shotglass to celebrate with.

At least some of the work is revolving around adapting the technology for communities that have very limited access to computers and computer power. A lot of my fellow repraps are seriously interested in the one laptop per child product, so I had been wondering how many robots could be controlled by a single computer. Thats where the idea of a small amount of memory installed as an intergrated part of the robot struck me as potentially useful.
Ghostwriter
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ghostwriter wrote:

I'm not quite sure how a digital-to-analog conversion would be useful here, or maybe I'm missing the application. I think you'd want to avoid any AD/DA conversion because it is inherently "lossy." Fabrication machines are really CNC devices, and should be controlled and monitored digitally. Controllers can be quite simple. You can operate most any CNC machine with a low-cost microcontroller, with the G-code (or other programming) steps stored in a few K of Flash. However, most people use a PC because the interaction with it is easier.
What, specifically, were you intending to control with the analog voltages that have been stored?
-- Gordon
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wrote:

A lot of it is simply trying to take my understanding of electronic control circuit and expand it to understand what the simplest method of control for something like this would be. My thinking is that when we attempt to simplify the hardware, dead recogning rather than complex feedback loops would be simplest. That may be impossible to "dial in" to sufficent tolerance to make it worth the effort.
Even if its not high enough tolerance to be acceptable to Americans, Africa is potentially a completely different story.
Ghostwriter
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snipped-for-privacy@gmail.com wrote:

You lost me.
In any case, for these types of systems tolerance is really more than exactness of sizing or measure. It's the difference between working and not working. Also, digital is usually cheaper, oddly enough.
-- Gordon
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