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Thread: Modding from TTL to Analogue

  1. #11
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    Isn't it easier to use the TEC part of the driver boards as is an to put in a new driver schematic for the LD which matches the current and voltage output?

    BTW: I'm looking for changing my green dpss from ttl to analogue. But I think in my case it could be more cost effective to just buy an analogue one.

  2. #12
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    I just get a throbing sensation... :Embarassed:
    Funny..... thats the feeling I get when I go to bed :lol:

    I've been to busy reverse engineering it to be bothered fixing it yet

    I will draw out the unpopulated area of the board (obviously with no values), there isn all that much missing, a few resistors and caps, a pot and an 8 pin soic chip.
    There are also a couple of resistors and caps missing in other places on the board, most of them in parallel with other resistors/caps. These could be different values that get used with the analogue mod.

    Would the frequency of the ttl blanking (10kHz) be fast enough to emulate analogue?

    Jim

  3. #13
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    Quote Originally Posted by JimBo
    Would the frequency of the ttl blanking (10kHz) be fast enough to emulate analogue?

    Jim
    If you mean emulating by using PWM to drive the TTL. Then I don't think so:
    10kHz, 8 bit: image you have intesity 1: thats 39 Hz pulses
    Intensity 128 (half power) that's 78 Hz pulses.

    If it would be a static beam, they yeah. But you beam is moving at high speeds. So this means you'll end up with a stripe pattern instead of something like analog modulation.

  4. #14
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    hehe, and i thought the Chinese were the ones good at reverse engineering
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  5. #15
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    Default Possible end-run around analog blanking modification problem

    Quote Originally Posted by marconi
    altho, You still would only get almost 10khz analog this way because of what they chose of output driver op-amp and output transistor
    They need to be changed out ... FET output would help too
    Hey Marconi;

    You mentioned something that I've been noodling on for some time. Rather than modifying the internals of the PSU to support analog modulation directly, what would prevent you from mounting a power mosfet right at the output of the existing PSU and using that to give you analog modulation? (You could build a voltage divider to knock down the zero-to-five volts of the analog blanking signal to somthing more reasonable - say, zero to 1 volts - and then apply that to the gate of your mosfet.)

    That way you'd still have all the current limiting capabilities of the existing PSU intact. And assuming that there wasn't any capacitance in the circuit downstream of the current regulator, you shouldn't ever have to worry about overcurrent. (The Mosfet isn't going to be able to pass any more current than the existing PSU can deliver.)

    So what do you think? Would it work? (Sure would be a cheap fix, since a nice power mosfet can be had for about a buck.)

    Heck, you could even bias the gate of the mosfet so that zero volts on the analog blanking line would drop the current down to just below lasing threshold, but would not completely kill it. That way you'd be in a better position to come back on at full power quickly. (Limit the blanking-induced power loss!) To complete kill the diode just hook the shutter control to the TTL blanking line on the PSU itself.

    Ok - tell me why it won't work...

    Adam

  6. #16
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    I've stripped the head down to see what is inside it, from what I can tell it has the laser diode at the back with a thermistor and TEC, then in the middle a lense presumably for focusing into the crystals, then the crystals along with another TEC and thermistor.

    Am I right?
    Can you just suply the diode with 5v to make sure it is ok?

    Jim

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    :? :? :? :?

  8. #18
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    Hi Guys
    I will try to use a few of your-alls quotes this way it wont get too messy..haha.

    Isn't it easier to use the TEC part of the driver boards as is an to put in a new driver schematic for the LD which matches the current and voltage output?
    Basically is what Ive been doing here, the problem is ..it takes up additional space
    requiring an additional box..
    Ive been trying to avoid this and use whats there already..cheaper..sometimes
    Also, By using the already established current settings it would make overdriving the diode less likely.
    Sure, some of us are smart enough to start at minimal current and crank it up to just what we need ..
    but if this is a blue laser..sometimes you get lost in the adjustments as temperature changes on the diode
    at diff current settings ..the blue lasers have such a small window of success on hitting the sweet-spot.

    Rather than modifying the internals of the PSU to support analog modulation directly, what would prevent you from mounting a power mosfet right at the output of the existing PSU and using that to give you analog modulation? (You could build a voltage divider to knock down the zero-to-five volts of the analog blanking signal to somthing more reasonable - say, zero to 1 volts - and then apply that to the gate of your mosfet.) [/qoute]

    Good question., Might be where we will end-up at ..
    At first look , it looks easy depending on the original setup of the board.
    Some are not so easy or have no room inside.

    Right now I have built a driver using a video op-amp and an mosfet for a TTL green laser and trying to avoid hacking up the original supply..(this is for Astroguys unit).
    works well..needs to be mounted to a beefier heatsink..but I think I will prolly also have to use an external 5v supply as the one included in his old supply is iffy.
    Dunno yet.. still tuning ..to me it seems like it would be all to easy to blow up the diode by overcurrent
    if the setting are not just right. seeing that I dont know what the original current draw is for the head unit which I dont have ..I will have to make a guess what that diode needs..
    This board I made is capable of doing a few amps easy.
    I did this so that later on..we all could maybe convert more of these units to analog without too much
    inside intervention and have plenty left over.

    Also, I the circuit I have is very linear ...smooth transitioning and fast.

    [qoute]Heck, you could even bias the gate of the mosfet so that zero volts on the analog blanking line would drop the current down to just below lasing threshold, but would not completely kill it. That way you'd be in a better position to come back on at full power quickly. (Limit the blanking-induced power loss!) To complete kill the diode just hook the shutter control to the TTL blanking line on the PSU itself.
    Doing that already in the op-amp driver...Plus DPSS lasers on their own all have different lasing threholds , I think this would have to be adjustable. Altho this also could be done in some software blanking settings too.
    Not going to rely on that tho...
    You are right..we dont want to turn the diode completely off..only just too our eyes.
    Its much easier on the diode..

    I've stripped the head down to see what is inside it, from what I can tell it has the laser diode at the back with a thermistor and TEC, then in the middle a lense presumably for focusing into the crystals, then the crystals along with another TEC and thermistor.
    You got it right...and looks almost identical to some of the blues from CNI I have.
    Mine have a anamophic prism pair inside as well.,, otherwise the same.
    One of mine has a bad diode TEC block...just barily makes temperature at low levels.
    Its the work- horse for experimenting as it also has a funky crystal set inside..I had to move them around the burn spot.
    My new one from spec looks the same as well but works perfect except its only good to about 8khz TTL,,ugh.

    Can you just suply the diode with 5v to make sure it is ok?
    Almost.. Just not 5volts only..but I think you meant the same thinking as the rest of us
    But checking the diode for output on a questional unit would also require some fancy tactics with a mirror
    and possibly removing the focusing optics to check the output.

    BTW: I'm looking for changing my green dpss from ttl to analogue. But I think in my case it could be more cost effective to just buy an analogue one.
    Almost seems that way... I know if I was to buy a new one again I would like to know exactly what the limits of modulation are...as it is now we are only told that some of the newer units will do up to 30khz.
    But I gotta see this for myself as I have recieved many that were NOT as quoted. !!!
    A scope pattern of the diode at 30khz input would be nice to see.

    but I think there has to be an easier way..Thats what Im trying here now.
    But at least I think we could figure out what they (CNI) and others have done in the TTL/analog units
    by figuring out the missing parts would get us closer to home and have usable units.
    But still..I want more .. I want to know that it will spit-out squarewaves at 30khz at 50/50 cleanly.
    without getting weaker or at least by eye not not have shadows or tails.
    I have seen where some manu's only have modulation from zero to abt 3.5volts..
    This makes it look brighter on dimmer transitions, but that dont fool me..


    I hope I didnt miss anything
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  9. #19
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    Quote Originally Posted by allthatwhichis
    :? :? :? :?
    Twice...

  10. #20
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    Hey Marconi;

    Great post! You did miss one part of my original question though.. I asked "...what would prevent you from mounting a power mosfet right at the output of the existing PSU and using that to give you analog modulation?"

    I understand that you'd want some biasing circuitry on the gate to adjust the "off" to be just below lasing threshold, and you'd probably need to drop the voltage range from the 0-5 volts coming out of the DAC to something like .1 to 1 volts for the gate, but that is easy enough to do. (In fact you mentioned something to that effect when you posted:
    Quote Originally Posted by marconi
    Doing that already in the op-amp driver...Plus DPSS lasers on their own all have different lasing threholds , I think this would have to be adjustable. Altho this also could be done in some software blanking settings too.
    Not going to rely on that tho...
    You are right..we dont want to turn the diode completely off..only just too our eyes.
    Its much easier on the diode..
    My point is that if a hobbyist wanted to do this for a SINGLE laser, it wouldn't matter that he would have to tinker around with the bias a bit in the begining to get everything correct. Once it was dialed in you'd be all set. I agree that it would be different for each laser, but I'm not looking for a mass-production product. A simple resistor network would do the job...

    So, ignoring for a moment the fact that the gate biasing circuitry is going to be slightly different for each laser, is there any fault with the basic idea of using a single power mosfet all by itself to provide analog blanking on the output of an existing TTL-only PSU?

    Adam

    Adam

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