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Thread: Revue - die4drive project

  1. #1
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    Default 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
    Last edited by 450nm; 09-19-2007 at 06:32.
    A lovely childhood. Just me my mother and the voices.

  2. #2
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    Default

    I've already built 2 of these and have 2 more on order. I never soldered any of those small components before but what I found worked for me was to tin the board then remove the solder with wick. Then use lots of liquid flux to make it sticky. Then I could hold the component in place with a small pointy thing and then with a small dab of solder on the iron, just touch where I wanted it to go. Then I'd do the other side or sides. Once it was all tacked in place I'd go back and add solder if needed.

    If you have a better method I'd like to hear it. I have heard of people using ovens. Has anyone tried that?

  3. #3
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    In similar fashion, I blob some solder onto one pad on the board, then hold the component in position with fine tweezers. Whilst applying heat to the solder blob, the component sinks onto position and is held fast while I run around the other pads. Finally returning to the original anchor for a last melt and kiss of fresh solder.

    Sorry for the excessively technical terms

  4. #4
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    yep ive got 2 third on its way
    Eat Sleep Lase Repeat


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  5. #5
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    Hi Andy, Just looked on your site and noted that you were complaining of a lack of voltage from the pcb.

    Iím not sure what you mean. I just checked and my 1.2 board gives the full 5V on open circuit (no diode in place).

    I have 2 small diodes and with one in place the volts across it is 2V and with the other it is 2.5. Surely the voltage is set by the characteristics of the diode?

    A lovely childhood. Just me my mother and the voices.

  6. #6
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    Quote Originally Posted by 450nm View Post
    Hi Andy, Just looked on your site and noted that you were complaining of a lack of voltage from the pcb.

    Iím not sure what you mean. I just checked and my 1.2 board gives the full 5V on open circuit (no diode in place).

    I have 2 small diodes and with one in place the volts across it is 2V and with the other it is 2.5. Surely the voltage is set by the characteristics of the diode?

    i have version 1 not 2. diodes need 3v and i found the board was giving out 2.5-2.7 v

    im sure version2 is fine
    Eat Sleep Lase Repeat


    Aluminium Optic Mounts

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  7. #7
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    Ah right, I don't have the circuit for V1. I just checked and the MOSFET has a DS resistance of .037 Ohms so with the 1R resistor and a 5Volt rail, I made it:-

    5 - (1.037X1.063) = 1.102331

    Which at Robins full rated output of 1063 mA would give 3.897669 Volts available across the diode which seems plenty to me.

    If I ever get a diode that will run it flat out I'll be able to measure everything with a meter to confirm

    Regards - Dave
    Last edited by 450nm; 09-19-2007 at 10:54.
    A lovely childhood. Just me my mother and the voices.

  8. #8
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    Re Carmangary comment is there a better way ??

    Well I dont know about better, but in our work on miniature electronics many solder systems have come and gone over the past ten years or so.
    Probably the best so far has been the small hot air system. I am not talking about the big expensive job with the various heads at an alarming cost but the simple little unit. Hakko make one type. You can get very simple solder and desolder joints with this device.
    The other comment re liquid flux (not plumbing stuff under any circumstances of course)... This is really good stuff.
    The real secret to a good job is a very clean PCB pad (clean with isopropyl alcohol) , pre tinned and cleaned off again with solder wick or similar. Clean then use liquid flux. With this method you can then get a small "ball" of solder on a "run" down the legs of the IC .. you can do this with just a standard smallish iron you will end up with very few bridges once you get the knack. Any bridges clean off with solderwick.
    Then hot air flow over the legs again if you have same and voila a perfect joint. Don't forget to clean up the flux after with isopropyl.
    We regularly (daily) do 100 pin + SMT IC's .. None of this gear is super expensive.
    Just remember clean, clean, clean liquid flux and your away. (oh and a bit of practise is not a bad idea before doing the real expensive bits)

    Cheers
    Ray
    NZ

  9. #9
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    Quote Originally Posted by andy_con View Post
    i have version 1 not 2. diodes need 3v and i found the board was giving out 2.5-2.7 v

    im sure version2 is fine
    ??
    Hi Andy,

    The driver outputs a current not a voltage.
    The voltage across the diode is determined by the forward drop of the diode at that current.
    The voltage compliance of the current source is supply minus I*R where R = on resistance of the MOSFET + 1R.
    From a 5V supply you should easily be able to drive a diode whose Vf is up to 3.5V

    Regards,
    Robin

  10. #10
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    LOL

    ahhh im not slating your driver Robin, its great.
    Eat Sleep Lase Repeat


    Aluminium Optic Mounts

    http://www.laser-man.co.uk/opticmounts/

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