I’ve googled but been flummoxed by too many hits, thought I’d take a short cut.
Does anyone have a circuit for a D-Type flip flop or shift register in discrete transistor/resistor logic, either bipolar or mosfet designs ok.
The idea is to create a integrate a small amount of discrete components consisting of the flipflop and some driver circuitry for a single LED or RGB trio. Then these boards can be chained together in adjustable lengths. A micro would sit at the end of the line chugging the serial data into the chain and when it stops (and goes onto another chain), the pattern remains. Could be a good sparkfun widget actually.
I know there are addressable LEDs, but these use little micros of their own, I’m hoping discrete logic will bring down the unit cost.
I’ve googled but been flummoxed by too many hits, thought I’d take a short cut.
Does anyone have a circuit for a D-Type flip flop or shift register in discrete transistor/resistor logic, either bipolar or mosfet designs ok.
The idea is to create a integrate a small amount of discrete components consisting of the flipflop and some driver circuitry for a single LED or RGB trio. Then these boards can be chained together in adjustable lengths. A micro would sit at the end of the line chugging the serial data into the chain and when it stops (and goes onto another chain), the pattern remains. Could be a good sparkfun widget actually.
I know there are addressable LEDs, but these use little micros of their own, I’m hoping discrete logic will bring down the unit cost.
Phil
For a single LED (1 color) you could use a 74HC74 as a 1-bit version of a 74HC595. If you needed to drive more than 5 mA, connect the FF's Q output to a logic-level N-ch MOSFET.
HC logic can deliver a lot more than 5 mA. There was a thread on this just recently.
I second that - why build from transistors? You can get 74HC595s for $0.25, quantity 1. If you need more drive, hook up a ULN2803. Pretty compact and cheap solution. chain in units of 8.
Philba:
HC logic can deliver a lot more than 5 mA. There was a thread on this just recently.
Thanks.
I second that - why build from transistors? You can get 74HC595s for $0.25, quantity 1. If you need more drive, hook up a ULN2803. Pretty compact and cheap solution. chain in units of 8.
If you don’t need the ULN2803’s 500mA/50V output, a TPIC6B595 replaces a 74HC595 + ULN2803. The TPIC6B595 doesn’t have the same pin out as a 74HC595, however. The TPIC6B595 open drain outputs handle 150mA/50v and also have a lower voltage drop than the outputs of the ULN2803.
Thanks for the tip on the 74HC74…it seems like the appropriate choice assuming it costs less than the discrete RTL logic and can be got in SMD packages.
Been doing a little more googling and the D flipflop seems quite complex compared to an RS flipflop in RTL in needing four transistors…then again maybe there are simpler RTL circuits or some other approach…I’d still like to see some RTL to get a baseline.
Ideally there’d be a single gate chip out there…not likely but would be nice.
No I’m not interested in using array registers like 74HC595 or string in sets or eight or whatever, I did think of that first. The extra outputs would be wasted. The whole idea is to have a single or triplet RGB LED with just enough logic to catch the LED state on as small a PCB as possible and physically distribute them wide and far. Of course if the price point is low enough then I’ll look at that.
Another reason is simply curiosity and a bit of retro engineering as an exercise in how those chips work underneath the black plastic.
Please tone down comments on drive chips it wasn’t the question, I can handle that, although the TPIC6B595 was interesting to hear about for non physically distributed applications.
actually, there are a number of logic chips that have a single gate. Fairchild calls it tinylogic. I think other companies have similar.
The problem with the TPIC6B595 is that it’s pretty pricey. Unless space is at a serious premium, it will be much cheaper to use the ULN with a 595. I wish there was a beefier version of the 74HC595 that could do 30 mA per pin and 240 mA overall.
Thanks…that looks just the ticket. One of those things, a transistor to buffer and we’re done. Minimal component implementation. I had no idea these things were actually made.