View Full Version : 1 color laser and a RGB signal, how do i wire this?

12-21-2017, 10:08
So the problem that i am having is that i have a 1 color laser (blue)
now if i project a circle that has red green and blue it only displays the blue part.
i want my laser to display the red and green part also as blue.

how can i wire this according to the ILDA pinout?
i assume just wiring the red green and blue pins together wont work, as a white signal would give a modulation signal of +15V then?

12-21-2017, 16:07
Most software will handle that for you but if not,
You might be able to use the intensity pin.
If that doesn't work and it is a TTL laser then you can use an OR gate.

12-23-2017, 05:23
Opamp summing amp. Add them up and when any color is on the laser will be on. You will need to take the signal from differential to single endedby just using the positive side of the signals. The output to the laser will then need to go back to differential. I like the drv134/137 chips. Real easy to use. See my post about Lorentz attractor for schematic.

You could try feeding the signals into 10k resistors and then tying them together for a passive mixer but I doubt it will work well. Do one set for positive and one set for the negative. Using 10k should...should prevent any damage. This approach is not recommended.

dump the output caps in their circuits orbit won’t work.

01-28-2018, 14:10
A passive mixer/selector with three 1K resistors and three schottky diodes will work, but you may see odd side effects with some drivers and you'll lose the low end of your signals. You don't want to sum the signals unless its your only choice, or if your doing abstracts, you just want to pick the highest signal of the three colors. If you do sum them you need to make sure the input to the projector never exceeds +5 volts and never dips below -0.6 volts.

TTL drivers instead of analog drivers with a 0-5V input are another matter...

I have a friend who designs IC chips for a living. I asked him to create the zero diode loss analog RGB to single color circuit for me. He came up with something that is beautiful and cheap to build.

You just need the first page of the PDF, although I'd add pull down resistors, unity gain buffers, and maybe 5.3V Zener clamp diodes to the inputs. I'd also add a 150 ohm series resistor and a Zener clamp to the outputs.

Its circuit and related simulation are attached...

So anyways, the core "Most Positive Signal" circuit is attached, but again, it needs unity gain input buffers, an output clamp, and some other features.

License is granted for private, non-corporate individuals to make their own boards for their personal home laser show use at their own risk . Commercial for profit or non-profit sales of this circuit or portions thereof without the express permission of and design review by S. Roberts and/or JT are forbidden. Least my name be associated with someone's untested "forked" design that damages projectors.

Get busy on the board layout for this if you want to, Kecked... But I want to see the proto functioning before you release it..

I'll post my usual passive RGB "select high" circuit later, I need to scan it in.


02-02-2018, 03:28
Why not just use a summing opamp with high value input resistors. Add a little gainand shove the diode on the output for crowbar. You can then just use a pot to keep the output below five bolts or a zener to clamp. Or a second stage to limit. Advantage is since you raised the signal up when you chop the diode drop and rescale, the diode drop affects the signal less.

Say you double to 10v. Now the diode drop is effectively half. If tha5 where germanium it’s 0.075v. Instead of 0.15v
0.075/5v=Is 1.5%. Heck the regular diode with none of this is 14%. This is much better.

Don’t forget to divide the input signals by three....

02-02-2018, 13:39
Because the voter circuit works down to "0" volts and uses the native scaling of the signal with almost no error or loss...

0.5V Red 1.0 volt green, 0.325V blue summed then divide by three for scaling...

0.5 + 1.0 + .325 = 1.825

1.825/ 3 = 0.608 volts, 40% lower then the 1.0 volt demand for green...

Please see attached for horrible old way that works, lousy circuit, but it works for most users if only driving ONE analog laser by an analog signal source. Most Chinese TTL lasers need an active pull down, basically a collector-emitter junction to ground on the sending end, so this circuit will not provide for that need.


02-02-2018, 15:39
Makes sense.........