I'm not sure if this will work or not, but it's a fairly simple idea, so maybe one of you who is familiar with mosfets could tell me if it would.
Okay, so the usual way of driving a lot of leds in a matrix is to multiplex them. But that results in each LED being on for maybe 1/8th of the time if you're driving an 8x8 matrix. And that means your LEDs will be dimmer than they would otherwise be. Of course you can drive the LEDs at a higher current to make up for this, or use driver IC's but let's say we don't want to use those methods for whatever reason.
So I was thinking, what else can you do? Well, what's the real issue with multiplexing? You can index a specific LED by row or column, but the LED turns off the moment you move to the next one, right? And that's why they are dimmer than normal. So might there be some way to keep them on after we move to the next one, and also turn them off at will, without using shift registers which would get expensive fast for a lot of LEDs?
That got me to remember flip flops and latches, but those are around twice as expensive as a mosfet, and are more complicated with five pins to the mosfet's three.
Anyway, I wondered if there weren't some way to use a single mosfet as a latch. What would happen if you took the output of a mosfet and routed it not only to an led, but also back to the mosfet's gate, via say a 10K resistor? And what if you also attached the gate to a microcontroller pin. And what if you set that pin high? Would the mosfet switch on? And what if you then let that pin float? Would it stay on? And if you then pulled the pin to ground... since the pullup is via a 10K the mosfet would then turn off, wouldn't it?
The above is probably some stupidly simple electronics circuit you learn in your first year of electronics but I didn't find anything when I googled for single transistor latch so I don't know what it would be called if it does work.
Anyhow, I haven't quite worked out yet how, if that can work, how I would then wire those into a matrix which I can index one transistor at a time. Cause the normal way you do that is pull up on one side of an led and pull down on the other with the rows and colums, but I'm not sure how you would do that with the transistors if one side always has to be grounded to keep it on when you're not fiddling with the gate.
So what do you think? Will the single transistor latch work at least? And can you see any way to put those in a matrix you can index row/column to flip them on and off?