How much signal.....?

[MechEng3]

One question. How many lasers could be run off a QM2000 card.....each modulation line before needing an op-amp to take the load off the card? This assumption running the lasers from a 50' ILDA cable. The issue of multiple lasers on one modulation signal line is the target. I just don't know what the output side of the board will stand. Let's say for instance you had 6 red lasers, 3 green lasers, and 4 blue lasers in one projector. Would there be enough voltage/milliamps to keep a good modulation signal over 50 or 100' cable?

[300EVIL]

You'd also need to figure in the impedance of the laser drivers modulation input. Though, my guess is most of them are high, K ohm to M ohm range.

I have seen a drastic improvement in signal just adding the color correction board to my system and I currently use a 6' ILDA cable.

[MechEng3]

Each laser is a little different....I have taken recordings of amperage at full mod with a power supply and the FB3 with a scope. I will locate the readings I have and go from there. I am not sure of the Laserwave needs as far as input impedance. I only have one of Bridge's drivers here to test. The color correction board would be a nice item to employ here.

[allthatwhichis]

Does the ILDA cable length make that much of a difference for laser modulation?

[Stuka]

I want to see THAT projector when it's done!!!

[laserist]

Is there a reason you don't want to consider buffering?

[Things]

Does the ILDA cable length make that much of a difference for laser modulation?

Over significant distances it can, I believe regular ribbon cable has a resistance of about .64 ohms / 10 FT.

[dave]

Does the ILDA cable length make that much of a difference for laser modulation?

It really all comes down to the input impedance of what's at the end of the cable. If the impedance is very high, the difference will be very negligible...

[FourDee]

Exactly. Even when you even have an input impedance of 10Kohm (which isn't much), and you have a cable impedance of 100ohms (which isn't a little) you only have a factor 100/10100 signal loss. So that's about 0.05 volts on a 5V signal ...

[mixedgas]

Exactly. Even when you even have an input impedance of 10Kohm (which isn't much), and you have a cable impedance of 100ohms (which isn't a little) you only have a factor 100/10100 signal loss. So that's about 0.05 volts on a 5V signal ...

It really comes down to the added capacitance of the parallel cables and how much Slew Rate Pango has on the opamps. If you have belden with individually shielded pairs and dont have those nasty lasers with autoswitching analog/ttl inputs with less then 1K impedance, then you wont see much of a problem.

But I have seen quite a few (and own one) lasers that have input impedance problems.

look, each channel of a buffer is one opamp, one protection zener for color, two protection zeners for X_Y signals, and maybe 5 resistors, it costs more for the DB connectors which have shot up in price and more for the board space then it does for the parts. 5 boards with 4 buffered outputs and interlock stuff with a 3 Day turnaround double sided were gonna be 250$ for SELEM minus parts. I have to pay my car insurance, so it didnt happen.

With 0 fast turnaround, and switching to surface mount except for the buffer chips, that would go down to less then 35$ a board, and the schematic is already entered into the software , but I would like to revise the layout quite a bit to minimize vias.

Steve