Revue - die4drive project
Well here's my own experience as a newcomer to the laser hobby.
I've always been fascinated with lasers since watching James Bond almost have his balls cut off with one years ago.
Some time back a relative bought a 1mW laser pen which I butchered to play with. At the time (about 7 years ago) these were far from cheap and I had lots of fun with it. I still have the diode but it is now very weak from the abuse that it has been subjected to including having the built in driver board blown to bits by 20 Volts. Surprisingly the diode lived.
I recently managed to get hold of a GVG-712 which is a fairly basic (but very effective) home/small hall tri-colour disco type unit. For want of something to do I also ripped an old cd burner to bits for the laser not knowing that a lens would also be needed which had ended up in the bin.
Having seen what can be done with 120 mW via the GVG, I then decided that I wanted to get a bit further into the hobby and build my own unit. I could of course buy ready made equipment from ebay but where's the fun in that?
I needed something that would drive the fairly chunky diode that I would buy at a later date if all went well. It would also need TTL/Analogue modulation capabilities as well as CW.
Looking around I came across the die4drive project by Robin Bowden which at £5 for the pcb plus the cost of components sounded ideal. The driver is adjustable giving constant current up to 1063 mA. Adequate for my intended purpose. A nice touch is the soft start feature which can be overridden if desired. It is claimed that soft start can extend diode life.
Being an electronics engineer by trade I had some experience with surface mount devices but as it is several years since I worked in the trade my sole tools were a small soldering iron, various small screwdrivers, a digital meter and a X9 watchmakers eyeglass.
Ordering the parts from Farnell turned out to be a bit of a juggle. Surface mount resistors come in batches of 50 etc and there is a minimum total order of £20 so I added a few extra bits to make it worth while. Notably an extra op-amp and MOSFET so that if the project went ok I could build a second driver or at least get a second go at trying to build one if things went wrong! Or looking at the project at bit more positively Including another pcb, would effectively give me two drivers for £30 which isn't at all bad. (I daresay the price could come down even further with a bit more juggling.)
When the pcb came I noticed that smd's had got a lot smaller since I last worked with them! Oh well, too late. I'd ordered it all now so had nothing to lose (except £30) by attacking the project.
At 57 my eyesight is not as good as it once was so I sellotaped a X9 watchmakers glass to the frame of my glasses and cleaned the point of my trusty soldering iron to a fine tip. There are much better tools for soldering smd's with than a 15 watt iron but I plodded on.
Sitting down with the various bits I wondered if I'd made a wise move but as things progressed it got easier. I put the smallest components on the pcb first which were the resistors. Last to go on was the MOSFET. I work on the principal that there is more room to manoeuvre this way as work progresses.
It was only after soldering a few resistors on that I remembered an old trick that greatly helped position the components. A pinhead attached to the smallest blob of Araldite possible held the component in place while it was soldered to the pcb. After 4 hours the pcb was complete and ready
to test and the excerise had been far easier than I had expected it to be.
To be on the safe side I stuck a 7805 in series with my Coutant variable PSU to keep any spikes at bay. I have had some bad experiences of dirty pots' in variable PSU's.
First thing to do is to decide what the maximum current the diode will need is and cut the 3 links on the pcb accordingly. Details are given on Robins site. As I only have small diodes to play with at present, I left all three links intact giving me a maximum of 146 mA to play with. No heat sink was needed but if it were to be run at high current a suitable heat sink should be used. There is a hole on the pcb to enable one to be bolted on.
The driver is very easy to set up. Just short the connections to the diodes anode and cathode apply power and connect a millivolt meter between MON and negative. The reading is simply translated as 1 millivolt = 1 milliamp. Adjust R2 to set the threshold (when the diode will JUST laser). After that link the TTL/Analogue to 5 Volts using the 'set' pad which will switch the diode hard on and again metering from ground to MON adjust R1 for whatever the maximum current rating is for the diode or whatever you want to limit the current to (see notes on current links).
I was extremely pleased that my driver worked first time. If time is taken putting the project together and each components connection to the pcb is checked with a meter as it is put in there isn't much chance that it won't won't work first time.
The driver certainly gives a much cleaner light than my previous arrangement of a resistor in series with the variable psu feeding a diode. As a beginner, I have no idea yet of the technical reasons why this should be so but it definitely is. Possibly noise being generated by the resistors?
All in all a very nice little project to start with. A bit of care and you shouldn't have any problems constructing it. I just need a decent diode and lens now!
I understand that Robin can also supply the driver ready built. Full details and schematic at:-
http://www.die4laser.com/
Revue by Dave
lasersonmymind@hotmail.com
