Help with 1 MHz Analog Laser Modulator

[SaltyRobot]

Now just to verify you did keep all other resistors the exact same value as in the schematic correct? If they are changed even slightly this changes the math drastically. Also it is a differencing amp not differential. Two totally different circuits. The differencing math seemed to be pretty simple as it mostly relies on plugging in resistor values and voltages at certain points in the circuit and then using division, multiplication and subtraction. No calculus needed.

What if you eliminate the op-amp and just do the constant current circuit in the data sheet for the LM317. What do you get then? This will help determine if the problem is in the LM or Op-amp side of the circuit. If you follow the data sheet exactly you should produce the current you are looking for however you will not be able to modulate it. If this test proves productive then we can move on to see why the Op-amp circuit is not responding correctly.

[roekeloos]

Hi good news. I bought a professional power supply at last I built the circuit without the Opamp and the output was as expected.

Using 3x 3ohms I got a max of 1.2A which is perfect. The multimeter still shows 0.4 over the dummy load so either my multimeter was broken or this dummy load is totally wrong.

But at least now I can see the current on the power supply. So the circuit was working all along! Yiihaa.

Things don't get warm anymore cause R11 is now 3x 3 watt resistors. And I'm using a lm338 with proper heatsinking.

Diode in copper aixis module gets really hot when running on 1A, really fast

Only problem now is that the modulation only works from 3-7V and not 0-5V. Does this have something to do with the pot or the R11 values?

Thanks for all replies again.

[roekeloos]

It working perfectly now. Pot sets the initial value for output. If pot at minimum modulation only starts above 3V. But with pot at about quarter way onwards modulation behaves as expected.

Now to build a electret microphone amplifier to amplify voice between 0-5V. And then to decode the laser modulation again. Aaaa why do I take on such projects. Thanks for all the help!!!!!

[steve-o]

Congrats and post some pix when u get it all up and running !
- And, welcome to PL

[SaltyRobot]

Hey that's great that you got this working. Please keep us up to date on how this driver works out for you.

Also where are located?

[roekeloos]

Hi.

Okay the modulation works from 0 to 0.7 A with a 0 - 5v input. And when I push the input to 9V I get up to 1A. That's strange because the 0-5V input is suppose to give me 0-1.2A out. Don't know if I'll be able to fix this because of time limit. I'd rather just work with a 0-9V input modulation.

This is for a artwork I'm working on. In essence the idea is to have the two tin can string telephone but the string is a laser. So far so good.

I'm from South - Africa and currently busy with a Masters in Interactive Media Design.

Thanks for great forum. Will post pics once installed.

[steve-o]

Really cool. There are other drivers available, one is called a flex-mod and the other is called Badpip. They are pre-assembled and available here on this forum. I'll find the links if you're interested. Sounds like an interesting project that you are working on.

[jammah]

hi I'm super interested in this too, I have acquired all the components needed for this driver Ill have a go at putting it together in the next few days
Id love to see pictures
james