TTL vs Analogue

[Alsone]

Hi,

Can anyone explain to me the disadvantage of TTl vs Analogue systems.

As I understand it the disadvantage is that the power of a TTL laser diode is always constant whereas with an analogue it can be varied.

However, I equally understand that the reason you might want to vary the power is to achieve white.

Which brings me to my next question, if you have a TTL projector thats balanced for white out of the box, is there any reason for not buying TTL in those circumstances as surely the full range of colours should be available to you in those circumstances.

[Stuka]

TTL lasers have 2 states - ON or OFF. So, with an RGB TTL rig, you basically get the 7 color combinations that the 3 lasers can give from either being on or off, and they'll always be operating at the full intensity of the laser.

With analog lasers, the intensity of each color is variable across the full operating range of the analog modulation signal, which gives potentially millions of color combinations with variable intensity.

[stanwax]

checkout the images here which show you the difference between analogue and ttl
http://www.stanwax.plus.com/lw/gloss..._analogue.html

Rob

[Stuka]

Hey, Rob -

COOL photo comparison - thanks for posting!!

Randy

[Alsone]

Hey guys,

Thanks.

Just wondered as I've seen some TTL lasers on ebay at great prices so thought could perhaps be tempted.

[FrankenPC]

Hey guys,

Thanks.

Just wondered as I've seen some TTL lasers on ebay at great prices so thought could perhaps be tempted.

I recently purchased a 250mw 532nm TTL laser. I then spoke to a Chinese EBAY supplier: http://stores.ebay.com/Snoc-Electronics
and asked him to send me a similar analog driver. I did a little soldering to swap out the current control resistors and I was all set. He sold the generic driver for 50$. He also sells other drivers from typical CNI laser systems.

Good to know.

[carmangary]

I use little die4drives for my red and green lasers. I think drlava has some analog drivers now, too.

[Speculative Lasers - Dan]

i have a 1W RGB TTL projector that i want to change to analogue, how much work is involved? do i just need to swap out a few resistors as mention above?

[stanwax]

there is a little more to it than swapping out a few resistors - though it can be implemented simply one of the main areas of difference if you want proper performance is in the tec control. Making the pump diode ramp up and down is pretty straight foward, but the temp of the xtals will more unpredicatable with analogue so the tec controller really needs some work too.
The effects of this will be noticed in scans as dark flickering patches and will be much more noticable on blue then green. The problem is that most tec controls (certainly on the chineese lasers I have seen) have single ended control of the tec so if the sensor tells them the xtals are too hot they can cool them down, but if the temp is too cool thay cannot heat up with the tec - this leads to the beam becoming unstable/noisy during the periods where the tec has no say in whats going on.
You can overcome this to some extent using a feed forward circuit that takes a portion of the modulation signal and uses it to warn the tec whats going to happen - though getting the balance of this right can be tricky.
Im not saying dont try this - cos I did Its just its not a 'simple' job but you may get lucky and find that your laser is quite happy with it.

Good luck

Rob

[FrankenPC]

there is a little more to it than swapping out a few resistors - though it can be implemented simply one of the main areas of difference if you want proper performance is in the tec control. Making the pump diode ramp up and down is pretty straight foward, but the temp of the xtals will more unpredicatable with analogue so the tec controller really needs some work too.
The effects of this will be noticed in scans as dark flickering patches and will be much more noticable on blue then green. The problem is that most tec controls (certainly on the chineese lasers I have seen) have single ended control of the tec so if the sensor tells them the xtals are too hot they can cool them down, but if the temp is too cool thay cannot heat up with the tec - this leads to the beam becoming unstable/noisy during the periods where the tec has no say in whats going on.
You can overcome this to some extent using a feed forward circuit that takes a portion of the modulation signal and uses it to warn the tec whats going to happen - though getting the balance of this right can be tricky.
Im not saying dont try this - cos I did Its just its not a 'simple' job but you may get lucky and find that your laser is quite happy with it.

Good luck

Rob

I would say it's not possible unless you are an EE.

BUT, you can aquire another powersupply geared for analog and swap out the current control resistors then do a little adjustment on the +5 (high signal) to get your power levels correct. Many of these cheap Chinese systems use common parts which are somewhat interchangeable.