Simple audio controlled stepper?

[ZeroPoint]

Hi guys. My main projector project is on hold for a bit due to lack of $$ so I'm hoping to throw something together with what I have for a house party I'm throwing tomorrow night... erm, I guess technically it would be tonight.. But anyway, I'm hoping to use my galvo set (a cheap 20kpps set from china) to make two single axis scanners. At the moment I have nothing to control it with so my idea is to feed it an audio signal from my stereo system. I just want it to make a simple fan that goes with the music. My dilemma is that I'm not sure, A) If this is logical (I dont know the currents involved in operating the motors so I don't know if the signal from the speakers will be adequate) and, B) How I would wire it to get the desired effect. I'm searching google right now to see what kind of schematics I can find because my set didn't come with anything as far as instructions/manuals/schematics. Of course it's not going to be as easy as feeding the + and - wires to the motors since there are 6 unlabelled pins on them, plus im not sure how to incorporate the PSU, amps and drivers into the idea. One of the main issues giving me doubt is the + and - input voltages. I'm assuming there is no spring return in the motors so they need both voltages in order to go in both directions. how would this work with a simple audio signal? If anyone has toyed with similar ideas or knows of anything that would help I would be eternally grateful for any response


Edit: As you can probably tell, this is my first time setting up any sort of galvo so I'm quite the noob. I should have looked at the set before posting this because most of it was very self explanatory but I'm still left with 2 questions. The only pins I'm still unsure of on the amp/drivers are a set of 3 labelled In+, In-, and G. I know what these means but I'm not sure how I would feed them in relation to my audio idea. Then there is another set of 3 labelled -15, 0V, and +15. Does anyone know what these are for? the amps are already being fed 24 volts from the psu and the galvos are already connected. If the In+ and In- are the signal inputs then what is the 15v for?

[ZeroPoint]

ok, scratch my entire previous post, i've got it working... sort of. It does exactly what i wanted it to do except that it is hardly noticeable. The input signal is so weak that it barely moves the scanner. turning up the bass and the volume helps but it is going to require me to turn it up well past the acceptable limit for my apartment at 2 in the morning lol. Is there possibly something I can adjust on the scanner amp so that it will increase the output?

[mixedgas]

Your galvo amp has 3 pin differential inputs designed for a +/- 5 or +/- 10 volt input. Forcing audio into one side of a diff input without driving the opposite side with a inverted mirror signal will cause your single ended audio signal to be canceled. They are noise canceling inputs You possibly just measured how well they cancel.

Open up the input gain pot on the amp. Apply your audio to the + input of the galvo amp (carefully) and ground the - input of the amp to the ground pin, and your return (ground) signal of the audio cable to ground on the galvo amp 3 pin input. When you ground the minus input on the galvo amps three pins, it makes the + input single ended and the galvo will now deflect.

I'm sure you know this by now, but....
Don't use the 8 ohm speaker outputs to drive your galvo amp, use the line outputs (RCA plug). If you use the speaker audio you have to AC couple it, and the 12-24 volt spikes from a ringing bass speaker could kill your galvo amp's inputs.

Peak signal at full blast out of a RCA jack should be about 600 mV, so not much deflection unless you open up the gain pot.

Here are typical galvo amps of a older generation,

http://www.skywise711.com/lasers/scanner/scanner.html

Second to last drawing in the set.

Steve





Steve

[polishedball]

If you use the speaker audio you have to AC couple it, and the 12-24 volt spikes from a ringing bass speaker could kill your galvo amp's inputs.


Steve

Wouldn't the speakers output be AC coupled already as to block the DC? wouldn't you basically need to DC couple it shorting the caps? Its early but was thinking it worked that way.

[mixedgas]

Wouldn't the speakers output be AC coupled already as to block the DC? wouldn't you basically need to DC couple it shorting the caps? Its early but was thinking it worked that way.

On singled ended amps, yes.. Perhaps on older or low cost systems as well.

Not that I would know, I have not done pro audio for a long time, however:

Lots of modern amps are DC servoed, and direct coupled via a Zobel matching network, etc. Even LM3866 based amps can have a optional DC servo these days. It does not mean the output response goes to DC. On startup, most amps without pop reduction swing to near one of the rails till the feedback loop kicks in.

example:

MY personal stereo amp is a 1U rack, passive cooled, switcher running class G or HIJK or something that can have massive voltage swings yet has a near DC to 63 Khz frequency response, yours for 135$ on closeout sale. Bridged on 4 ohms it does 160 watts, and I'm not talking marketing peak watts... It does tricks like reduce its supply rails on low passages, etc. Its schmart(tm) :-)


Steve