8 Led sequence, forth and back.

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Dagon

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Hello guys, well I have a problem, this circuit:

There are 8 leds, when led 1 is on all others are off, when 2 is on all others are off, etc. It must start in led 1 and end in led 8 and then go back to led 7, 6, 5 etc to led 1 and so on.

(If you have Circuit Maker is the Led.ckt file just bigger -8 Leds-).

I have to do this without the Data Sequencer, just using flip flops, gates, etc.

Thanks in advance for your help. :wink:
 
You can do this with a simple shift register. Each clock you shift in another '1'. When all the LED's are lit toggle a direction bit in a flipflop that causes '0's to be shifted in from the other side.
 
Thanks for your fast reply, but sorry I can't follow you.
I'm a newb at this.

Could someone make an schematic if possiple, thanks.
 
Anyone? I have tried with flip flops and a pulser, but only 2 leds work, the others take too long and don't go off. :cry:
 
Hi

It will be super easy to make it in a MCU.
Anyway, here is what I come up. :arrow:

Good Luck

STEVE
 

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Here's my attempt. The resistor/capacitor will set how fast it will go. The 8 wires on the right go to the 8 LEDs. The 2 gates at the top are NOR gates even though they look like NANDs.

Mike.
Edit made image bigger so numbers can be read.
 
Last edited:
Hi Pmmie,
Don't use both inputs on the 4093 Schmitt oscillator. Connect one input to its positive supply. You can use the 4093 for the flip-flop too.

If you don't use current-limiting resistors for the LEDs, the LEDs will load-down the output and the flip-flop won't work. Current-limiting resistors woill reduce the brightnes way down, so buffer each output that feeds the flip-flop with a couple of inverters or emitter-follower with current-limiting resistor to drive its LED.
 
audioguru said:
Hi Pmmie,
You can use the 4093 for the flip-flop too.
Click to expand...

Not really. If you use nand gates for the bistable latch then the inputs are active low rather than active high. In other words, the inputs have to be held high and one of them taken low to activate it.

This brought back some memories, I think it's 20 years since I last worked with discreet CMOS.

As someone else said, it's a doddle with a microcontroller.

Mike.
 
Hi Pommie,
Of course you are correct. I saw your symbol for a Nand flip-flop and forgot a 4001 is a Nor.
Are most of the LEDs driven directly from the 4028 without current-limiting resistors? Are the LEDs bright enough? What supply voltage?
 
I doubt CMOS will drive anything direct. If I remember correct, the B series were buffered, which meant they could supply more current - still I doubt it would drive an LED at any reasonable brightness. I assumed this was a logic exercise and therefore we didn't worry about such trivial matters as driving capability. :roll:


Mike.
Edit, The NAND symbol is what is drawn be Eagle as a NOR. That's what you get for using free software. - Still a very useful program though.
 
With a 9V battery I directly drive fairly bright LEDs from B-series Cmos all the time. 8 to 10mA isn't bad. Try it. Sometimes I parallel a couple of gates or inverters in the same package for extra brightness.
 
As I said in an earlier post, I haven't used CMOS for about 20 years, I'm now far to lazy and just do everything with a pic chip.

Mike.
Edit, Just read the post and it could be construed as I'm knocking CMOS. I'm not, I grew up on it and it's a great way to learn logic. If you can design it with gates, it will be a walk in the park to do it in assembler :twisted: .
 

A PIC is CMOS anyway :lol:
 
[quote="Nigel Goodwin]
A PIC is CMOS anyway :lol:[/quote]

Touche. In my defence, it is now 1:30 in the morning - I've had far too many stubies and I should go to bed.

Good night

Mike.
 
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