Hey super smart fellas! It's a long story, but I have my hands on about 100 74HC4067's (16-channel multiplexer/demultiplexer).
I need to drive a 16x16 matrix of IR LEDs (LTE-5208A, 100ma). I imagine I can use one of the 4067's to select the row, but does anyone have any suggestions for the column side of things? Maybe a set of transistors to pull it down to ground? I don't need PWM and my biggest concern is speed (so pref. no SPI, I2C chips).
Also, fwiw, typically only one will be on at a time, maybe two, my point is that I don't need a huge 2A per column or anything. Additionally, it would be nice to be able to select any point arbitrarily, as opposed to cycling with something like a shift register.
I'll be driving all this from a Due, fwiw (and got plenty of logic level converters)
Set up 4 address lines and common pin, bring E/ low, and one of 16 outputs will follow the common pin.
(I show the INH line as 1 high and 1 low, that is not correct, that is the E/ pin).
Ahh.. I think I gotcha, so the "Common Input/Output" (Pin 1) on the left would be set to +5, and the same pin on the bottom would be set to GND, making it a sink?
Regarding the E/, I would imagine it could stay down on both unless I really wanted all the lights off.
Ya know, sometimes.. it's the easiest solutions that escape you
Regarding the 25ma limit, should I just through some transistors in there? The only thing is I would like them fast (<60ns), maybe a few 2N2710's? Any suggestions of some driver ICs? The one I'm most comfortable with is the ULN2003, but it seems slow and a bit overkill.
By the way, thanks so much for all ya do, I see ya all over the forums, and I doubt there's as many people out there who actually whip up schematics for folks to help them out, so thanks again!
Ahh.. I think I gotcha, so the "Common Input/Output" (Pin 1) on the left would be set to +5, and the same pin on the bottom would be set to GND, making it a sink?
Yes.
Regarding the 25ma limit, should I just through some transistors in there?
Note that a transistor will invert the signal so give it a logic one and it conducts. ( NPN )
Re: Transistors.
You'd need a PNP controlled by left side to source current (low = On), and NPN controlled by bottom to sink current (high = On).
This also introduces some different Vce losses into the signal path, so you'll need to look at that:
Vsource - Vce(PNP) - Vf (LED) - Vce (NPN)
Is the result positive?
If not, may have to consider another transistor, or perhaps a Logic Level, Low Rds MOSFET.
