OP Amp Buffer

[mikkojay]

Hey Guys,
I am getting pretty close to firing up the lumia box, and I am getting to the point where I am plotting out the method I would like to control the intensities of the individual lasers contained inside.
The box will have 7 individual lasers total, all analog modulated.
I have one of these midi decoders, which has 8 TTL outputs and 4 10k potentiometer outputs.
Since the wipers on the 4 pot outputs only support 1ma each, I am thinking of buffering them with a quad op amp in a voltage follower configuration.
That will buffer the 4 variable 5vdc outputs OK, but I am wondering what the best option would be to pass them to 1 of 7 lasers based on the state of the 8 available TTL outputs.
I am not too worried about only being able to run 4 of the 7 lasers simultaneously, I would just like to come up with the cleanest way to do it.
I was thinking of "punting" for the time being, and making 4 of the 7 analog modulated and the remaining 3 just on/off using 3 of the available TTL lines, but that would not be exactly what I am looking for.

Just to be clear, I would like to have 4 sliders on the midi controller vary the intensity of 4 of 7 lasers. Which 4 of the 7 will be selectable using up to 8 TTL hi/lo outputs that I can generate from switches on the midi controller. Shouldn't be too bad- I just hope I have the parts I need so I don't have to end up ordering online and waiting like usual. I am not at home right now, I am sitting in a surgery waiting room on my laptop- my dad just had both of his knees replaced (went good, he'll still kick my ass on the golf course I am sure)

If anyone has an idea for this, I would appreciate your input.
Thanks!
-Mike

[mikkojay]

OK, I think I will try this- I'll just use 4 npn's to control 4 5vdc spdt relays, and attach the output from the op amps to the common pole of the relay. I will attach 1 laser modulation input to the normally open pole, and one to the normally closed pole. That ought to do it & be simple.
Stupid Radio Shack wants 5 bucks a piece for the relays though!
-Mike

[drlava]

there are many ways to solve this, some more complex than others but here's a simple way: use some of the digital lines to control an analog demultiplexor or two.

here's the cheapest DIP analog mux/demux I found on digikey (55 cents):
http://search.digikey.com/scripts/Dk...=568-1455-5-ND

You might need pull up resistors on the TTl lines and pull downs on the outputs.

[mikkojay]

Hey thanks for the reply Andrew- I was hoping you would see this one
I was also wondering about the pull up/down resistors- I will check out that IC & do a little experimenting.
Since I just got my midi controller, I suppose I will have some time to wait for a component to show up while I figure out how to map the keys & put together the buffer part anyway.
Its getting to that point where I am in the stretch, but I suppose I should be careful to not cut corners and do something hastily/crappy just because I am anxious to see some nebulas.
Thanks, Mike