Steve Anderson wrote:[
Harry, if you're getting 'wrong polarity' light when modulated, just reverse the inputs to the LM311, feedback isn't used so it's of no consequence to the '311 which way around the inputs are.
Below is my suggestion, this should be good for up to a 300mA laser, the BC107 200mA. The 2N2222 will drop one ot two hundred mV, so allow for that. I've drawn a red laser...but I'm sure you know what I mean...R110 would of course be a low-value preset in practice...make sure it doesn't go open-circuit (the usual failure mode of presets) otherwise say goodbye to the laser...eventually fit a couple of fixed resistors in its place to give the correct voltage out of the LM317...
The diode and 47 Ohm resistor is drawn wrong...sorry to point that out...
Steve A.
Hi Steve
Just to let you and all know how its going ...I finished the modulation circuit but as i said been fault finding ..first up i stuffed up on your PWM 555 timer diode after the timers out put it was mis shaping the ramp which ended up being i used a tiny zener diode by mistake ...so fixed that .
For the transistor circuit after the LM311 I didn't have a 2n2222 and used a BC107 ..guess what again a no goer !No mistakes this time just didn't work these Violet uv Lasers are fussy ...I went looking in my junk box of transistors and tested about 100 to see which bugger would switch the laser on in a transistor switch circuit ...so i have ended up using an old 2sb400 transistor radio metal can type must be from the 60's or 70's..but works the other i could of used but theres no data i could find onit Fmps2369 one other so warn could not read the type but its another old am radio can type trany.
Modulating these buggers is harder than i was expecting live and learn !
I first up tested the laser to see it if was working modulating with a pc signal generator first low frequency pulses to see it flashing by eye up to 10hz...next up to higher frequencies and manually sweeping the laser across a spare glow tin and i can see the gaps in the pulses so that lasers switching ok via Steves circuit and the other circuits .
Did it again with a SSTV signal i can see the gaps or differences in major light level changes on my glow tin .
Now Steve i inverted the inputs to the LM311 but
Because i used a 555 timer last time that inverted the video signal ...now not using that and doing the above i inverted it again !!!!!!! Yakes tell you what since i will be trying photos i will invert them and that should fix it without more soldering ...
I can see thinking things will get easier when i do the scanning is not going to happen so expect horizontal trouble shooting next .