Betting on red or black

We made and tested the new laser circuit driver and the good news is that it works fine even better than MKI prototype. The isolation of the analog and digital circuits produces a free-of-noise FE signal which allow us to focus really better and which more accuracy than in previous versions. Analyzing the signal with the oscilloscope we saw that we don’t almost have any noise, only a small background RF noise probably generated by the environment.

The bad news is that unfortunally we could not focus with the red laser.

We limited the current diode with a resistor but the S-curve we observed at the oscilloscope was very small. So we were decreasing the resistor in order to increase the current and obtain a better S-Curve amplitude. But at some level the diode destroyed itself again. So, we think probably the red diode and its electronics provides a lower gain than the blue one and we should amplify it more if we want to obtain a usable S-Curve, because it’s not possible to increase the luminosity of the diode without destroyed it. We decided to leave this improvement to other people interested on that and we will continue with our goal which is try focus with the blue diode which works fine. So we will bet all on blue (better than black).

There are two possibilities using the blue laser: focus on the PCB surface on some ground areas reserved for this task, for example near the screw holes. Or focus in some specific focus points outside the PCB. We must use again the glass with the protective film because it’s not possible to focus with the pickup mask.

First option it’s easier but we loose some small areas on our PCB designs. Second is more laborious because we have to make this small focus points and attached them to the fixture plate close to the PCB. Then indicate to the software where they are because the position will depend on PCB size. We are going to test both and see how they works and how easy are to use it.