Pots for Y+ and Y- / X+ and X-

[Phredy1]

Could I use pots for adjusting the X and Y sizes when using a sound card dac playing converted ADAT shows?

I was thinking of putting a pot in the Y+ and Y- and I should be able to use those to adjust my height correct? Same for adjusting the left / right with the X+ and X-?

Any suggestions on what pots to use?

Gene

[-bart-]

The cmrr of the input amps is very dependent on both x- and x+ being exact opposites.
It will be hard to achieve this with two pots.

Not really a problem if you run short cables.
If you value hum suppression and run long cables, high cmrr is preferred.

[chad]

Sure you can. You just need to use a duel gang pot for each -+ on x and y.

Like this:


chad

[mixedgas]

For once (and perhaps the only time, in your life) the Shack is your friend. These work good. So you need to chuck the matching knob in a drill press and drill it out .010 more, no big deal.

http://www.radioshack.com/product/in...ductId=2062359

100K dual, and even the new metric ones are very good.

Need short cables, to a certain extent, or buffers at the sending end for long runs, but still not bad.


Steve

[Phredy1]

Need short cables, to a certain extent, or buffers at the sending end for long runs, but still not bad.

2 questions:

1. Do I need to use the grounds on the pots or can I just leave those with no ground connected to them? If yes I need to ground, to pin 25?

2. I use a 50' cable. Too long?

Thanks!

[catalanjo]

2 questions:

1. Do I need to use the grounds on the pots or can I just leave those with no ground connected to them? If yes I need to ground, to pin 25?

2. I use a 50' cable. Too long?

Thanks!

1. Best use 0vdc rather than ground on the pots.
Wiper = output, input signal one end, 0vdc other end.
If you want to use ground for something try grounding one end only of shielded cable.

2. Depends so much on surrounding em noise that this would be difficult to answer correctly. Best try it and see! Worse case scenario you would need to buffer the sending end as Steve suggested. If you do this you would not necessarily need double pots since you would attenuate the single sided input signal to a buffer/inverter.
This also has the advantage of giving you the possibility of increasing the output signal for any insensitive scan amps and also gives exactly inverted outputs instead of approximately inverted outputs. (Double linear pots are never "exact" twins.)
Trouble is that a laser bounced off a scanner is one of the most sensitive galvos you're ever likely to meet.

PS.
1) Do NOT use logarithmic sound pots.
2) If you are installing pots might as well install inverter switches for back to front and upside down.
3) You might want to consider offset pots as well if you go down the "buffering" route.
4) Buffering only involves quad op amp chips (and sockets) and a few resistors but does require a +&- psu.

Best of luck

Cheers

[Phredy1]

I had all ready thought of putting a DPDT switch in to invert X, but never gave much thought to invert Y. I guess if the projector was ever hung upside down that would be the need to invert Y. The invert X came into the plan when I was thinking of projecting onto scrim.

This started out in my mind being a fairly simple idea, but like normal my ideas get more complicated when I try to put them into a build. I think I will just try Steve's suggestion for the double gang pot and see what happens. What is the worst that could happen? Or should I even go down that road.....LOL

Thanks for all the advice!

[mixedgas]

The worse that happens is you waste a gallon of gas, a hour of your time, and less then 10$ on a radio shack potentiometer and two db25 connectors. call ahead and make sure they have it in stock.

Steve

[catalanjo]

I complicate mine even further by hanging multi turn trim pots on the main pots so as to be able to choose the "range of the main adjust. (sometimes get "glitches" in the track just in the wrong place, and thats an itch you can't scratch in real time.

Good luck

Cheers
PS Isn't " a gallon of gas," worth more than a laser these days ??

[Phredy1]

I spent a few hours driving around looking for pots and nothing. A ton of singles and some duals, but no dual linear pots anywhere that I could find.

Would this work?



$1 each from Futurlec!

Gene