741 Op-amp wiring help please?! :)

[Stuka]

Thanks, thats a really useful articel however I'm not sure that solution is going to work.

I've already tried using a RS232 jumper box between the ilda cable and the ilda connector on the projector but it doesn't give any results at all unless its wired in the regular way (X sig to 1, X gnd to 14)

I suspect that if i had differential ouputs then switching the -ve to pin 1 would do the trick but I don't.
.....

With that in mind, how about using a differential amp for the FB3, instead of a signal inverter? (That is also discussed in Bill Benner's article, plus I believe it is also used in the FB3-based rigs the guys use at LaserShowParts / Lumina VP. I plan on building the op-amp circuit for my FB3).

If you used that, you should be able to then use the toggle switch as needed to invert the X-axis.

Just another idea to throw your way! Your inverter circuit will probably work fine, too!

[James Lehman]

Hmmmm. I thought I was the only one on Earth using scanners with single ended inputs!

http://www.akrobiz.com/laserboy/p_laserboy_33.html

I made a new front end board for my scanner amps. My amps take both +/-28VDC and +/-15VDC, The +/-15VDC come from external voltage regulators. Since I knew these scanner amps were single ended, and as a matter of fact my rig was originally designed to hang up-side-down. I also put unity gain inverters on each axis. I can flip the axis simply by moving the little blue jumpers.

EDIT: The op-amp here is a dual. It's a TLO72, I think.

James.

[afrob]

DO NOT USE 741 OPAMPS.
The 741 was developed in 1968 and is the third integrated operational amplifier ever developed. It will severely degrade audio frequency signals even in a unity gain configuration. You know, integrated circuits have advanced a little bit in the last 40 Years...

20€cent,
afrob

[norty303]

DO NOT USE 741 OPAMPS.

Too late, besides I believe this is what Bill at Pango suggested for Jimbo, who sent me the diagram.

[norty303]

Ok, so after one slightly ugly attempt and a blown 741 (I think - some 12v connections got 'muddled' resulting in nothing but a very thin image vertically) I've now made up a nice neater version on a board and it works great....

...apart from the image is shifted down from the horizontal plane by a reasonable amount. If i remove the power to the opamp then the image reverts to its normal state in the middle so its definately something associated with the opamp

I can think of 2 things that are different from the diagram which might cause it but have no idea if its possible they are cause.

1. The diagram suggests up to 15v, but i only have 18v or 12v off my psu so i used the 12v.

2. I bought a big pack of mixed resistors and the closest it had to 5k1 was 4k7 so i used one of those instead. Could this cause the shift?

I now have some 5k1 resistors but wanted to know if that might be th reason before i tear it apart again.

Thanks for any advice you can give and any you've given so far!! If it wasn't for this forum I'd never have even attempted any electronics, and its been a fun couple of nights with my soldering iron!

[James Lehman]

You need both positive and negative voltages with reference to ground.

The shift you see is a DC offset created by the fact that you don't have it powered properly.



James.

[norty303]

Ok, that makes sense.

Any idea which pin it might be that i need to connect the -12v to?

The diagram below does only show the Gnd and +V

Or should pin 4 go to the -ve rather than the Gnd?

[James Lehman]

Sure.

You need to put -12V on pin 4 and ground pin 3.

Get rid of the 5.1K resister, and while you're at it use a better op-amp!

James.

[colouredmirrorball]

Thanks for any advice you can give and any you've given so far!! If it wasn't for this forum I'd never have even attempted any electronics, and its been a fun couple of nights with my soldering iron!

... and a lot of fried fingers! (I tried to repair a simple headphone by myself... it still hurts)
I'm afraid I can't help you, mate. I don't know anything about scanners. Will soon change!

[James Lehman]

To anyone who wants to learn how to solder, may I suggest getting some electronics junk out of a dumpster! It's free and you can't make it any more useless than it already is! You can get a lot of good practice removing and adding stuff. If you really want to get into repairing stuff, it involves a lot of part removal. That is in may cases more challenging than adding new parts. Plus, you would be surprised at the value of some of the parts you can recover from junk.

James.