NEED HELP IN A BAD WAY.... LED PROJECT

[telephoneman]

is there a chip out there to drive 7 -10 leds that will count pulses from a 555 and hold the lights on until the last pulse and restart? working on a project for school and having trouble finding the right chip to make the project do what my instructor is asking for. tried a 3915 with a capacitor to make the same effect but he would like to see if i can find something drive by a 555.  PLEASE HELP.

 

[AN920]

I don't know about a single chip apart from a micro. Discrete it could be done with a row of D-type flip-flops wired as serial-in-serial-out (SISO) shift register and clocked by the 555. You may also use 2X 8bit shift register chips with the proper feedback after 10 stages.

View attachment 40339

 

[Fowkc]

Sounds similar to a project I did for GCSE. I had the 555 clock a 4017 decade counter. Each output was connected to a thyristor that turned an LED on. Thus after 10 pulses, all the LEDs were on. It's not the ideal solution, because it requires 10 discrete thyristors, but it worked.

 

[AN920]

Also there will be a problem to turn off the scr's when the count restarts.

 

[Fowkc]

Hmmm... can't remember how I got round that... perhaps it wasn't an issue, not sure - it was a good few years ago!

But there must be a way around that problem. The last 4017 output could be used to turn on a PNP transistor to switch the SCR power on. When that output goes high, the transistors turn off and the SCRs reset. Again, it's not elegant (you only get 9 outputs), but it probably works.

 

[telephoneman]

thanks for all the help so far... i'll see if i can get something going.. if anyone has anymore ideas... i'd love to hear them....  THANK AGAIN.

 

[AN920]

You can do it many ways, some less elegant than others.

 

[aries1470]

is there a chip out there to drive 7 -10 leds that will count pulses from a 555 and hold the lights on until the last pulse and restart? working on a project for school and having trouble finding the right chip to make the project do what my instructor is asking for. tried a 3915 with a capacitor to make the same effect but he would like to see if i can find something drive by a 555.  PLEASE HELP.

Hmm... why not use a simple decade counter? and instead of using an LED, re-route the output to keep the appropriate led's on in order from 0-9?
Here is a simple circuit here, but just try to think on how to 'convert' it... ;-)
http://www.aaroncake.net/circuits/counter.htm
I will leave that part up to you :-D it is a very simple circuit and ready to take a pulse from a 555 timer too. just remember to keep your voltages within limits.

 

[ante1]

You might be able to use the UAA180.