Modulation

[planters]

I recently received some Flexmod P3 drivers and tested both a LOC-815 diode and a Nichia 445 diode. The driver is nicely constructed and works well. Set up is easy. When applying a (+) V to the modulation lead there is a linear increase in current output up to the user defined maximum which is reached when at (+)5 V. vs. ground. However, when using Q. Show and attempting to control output by attaching the modulation lead to pin 5 ( or 6 or 7 ) on the ILDA DB25 connector output from the computer, the laser modulates well ie. no trails between objects or within structures. But, the brightness is only 1/2 of what it is when applying a fixed (+)5 V. signal. I suspect that I am only modulating to (+) 2.5 V. vs. the Flexmod ground. I do not have an oscilloscope and so I can't check this. Should I connect the R-, G- or B- to the Flexmod ground? Should I connect the DB25 pin 25 ( ground ) to the Flexmod ground?

 

[Bluefan]

I'm surprised you got this far. From what I understand you have the current regulator for the laser diode running on a floating power supply (batteries for example). The ILDA interface is probably ground referenced. Connecting only a single lead between to a floating system won't get a signal to the other side.
The modulation signals from the ILDA are referenced to some zero point. I'm not familiar with the ILDA standard, but the modulation signal is either from - to + or ground to +. Both need to be connected or the driver on the other side doesn't see a voltage. Remember that voltage is always a two terminal thing.
Two non-floating systems can't be connected carelessly. Connecting a floating system with a single wire will just put that complete system at that potential, it won't get a signal there.

I'm probably not very clear