suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.
I'm trying to brainstorm how to go about measuring the current at the diode. On a test load, current is measured at the resistor. But without a test load, is it as simple as measuring across positive and negative leads of the diode? Maybe I'm under thinking this, do I need a test load in place of the diode to measure current?
suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.
Better late than never... I thought I'd answered it anyway, but it was another one. Bit of deja vu for a moment...
Anyway, try a 1R resistor (1% metal film or better) in series with the laser diode. Then measure millivolts across that. As the diode's current is controlled, you will get a millivolt per milliamp reading on a volt meter without upsetting the diode current, or risking ESD by interrupting the circuit. A Lasorb across the diode helps, but so will some small value low ESR ceramic capacitor, as between that and the 1R resistor you'll get a low pass filter that will reduce very short spikes to insignificance wile leaving your fast modulation capability unaffected. Adding that 1R is not required, but in any system intended for experiment, modification, monitoring, it's a good idea to include it. It may not matter which side of the diode you insert it into either, but on a high-side driver you might want to sacrifice its ESD-resisting capability if you're careful and find it more convenient to put it on the ground side. For a handheld meter you would not do this, but you probably should if you want to scope waveforms with the scope and driver sharing a common ground.
Most drivers use a sense resistor that carries full current anyway, and you could read voltage across that, but you'll have to know its resistance and apply Ohm's law to get a current reading. If it's resistance is extremely low, you'll need a very accurate millivoltmeter too. Using 1R in series with the laser diode allows any cheap meter to work well enough.
I do. And you would have, in different circs. You're keen, you'll pick it up faster than most if you stay keen long enough. Electronics are usually cheaper than lasers too (and when I first got into electronics, the closest I could get to a laser was a diagram of a helical flash tube around a ruby rod in a book in the Ipswich library. They didn't even have a photo. How sad is that?! Not knocking Ipswich though. Damn good library..) What got me hooked on the join between electronics and light? Little neon bulbs. I kid you not. I studied whole books on thw weird ideas people came up with for using them. Most forgotten now.
Thanks
I used to play with fluorescent tubes and RF but I could never afford to get into lasers, despite the desire. I think I've come into lasers at the right time of life though. I have a little expendable income, have caused enough injuries to myself to avoid burnt retinae and have the sticking power to learn all these complex lasery technicalities.
If it weren't for PL it might be a different story though.
Indeed. For me it was Sam's LaserFAQ that did it. I mean, there were a couple of books at Maplin for 20 quid a time, and plans from 'Information Unlimited' that I was wise enough to pay for only once. And then there was the LaserFAQ, with free access. It's like living in a world where people charge a lot of money for a basic look at something, and then someone opens a gold mine to the public and lets you keep any nuggets you find. No possible contest, is there?