How do ttl lasers work with showcards?

[grantanthony]

I'm reading about lasers and see there are analog and ttl lasers/drivers... with the ttl lasers usually being far less expensive than analog setups.

What I'm wondering is how these ttl lasers work with showcards? Unless I'm mistaken, a showcard is basically a USB to analog output... typically with the outputs conforming to the ILDA standard and via a ILDA connector (parallel port). You could theoretically control the ttl laser via these means (the differential p-p 5v analog signal), but your pwm capabilities would be rather limited compared to connecting the ttl lines up to a digital pwm pin on the showcard's microcontroller due to a limited dac update rate.

So.. how does this work? Does this setup require some sort of analog->ttl converter board on the laser side? Are ttl lasers simply not used?

Thank you

[grantanthony]

And a follow up question...

I have two green <50mW lasers I bought off ebay (but from american sellers and allegedly american based businesses). Random side note.. both said they had IR filters but that was absolutely not the case.

Both lasers are embedded in a heatsink and one even has a fan... but even after running these things for 8 hours they are still cool to the touch. What's the point of the heatsinks and fan? All I can think is it's either marketing.. or they are sold this way to get around some legal restrictions, but still allow you to crank them up to be far stronger than 50mW.

I would appreciate your thoughts.

[colouredmirrorball]

Hi,

Yes, most setups with a DAC tend to not use TTL lasers. TTL lasers switch on (or off if they're really cheap) at a certain treshold voltage. I don't have a clue how many volts that is and I guess it depends on the laser. This means that if you work with colour gradients, you can lose part of the image where the signal is under this offset voltage.

Most decent software packets have an option to only give TTL signals (only full on or off), so no analog to TTL convertor is needed.

Also, how do you know it's not because of those heatsinks and fans the lasers are running cool? :P
Cranking them up is on your own risk.

[mixedgas]

True TTL turns on at 2.4 volts and OFF at ~ .60

So it has to fall to less then .60 to turn off (Some Caveats apply beyound the scope of this post)

In practice I've seen the Chinese use other voltage levels.

The Pangolin card will usually drive a TTL input just fine. However what you get may not be what you want.

Some cards have a TTl level blanking signal besides the analog.

I have simple circuits to clean this up (Opamp Scmidt triggers) that you can build.

Steve