Hello all,

This is my first post so I would like to start by saying thank you! This is a great forum and I've learned a lot by just reading other people's threads. However to this problem I couldn't find any help for at least by searching.

Anyway I'm working on this LED sequencer circuit. Here's the original schematic by Bill Bowden (http://www.bowdenshobbycircuits.info/page5.htm#shift.gif):

I'm using this circuit because I need a rather long sequence with 45 or even 54 steps. This circuit seemed to fit my purpose ok.

However I would like to add some delay after the last step. Now it just keeps on repeating the sequence instantly. The delay time could be anything from 1 to 10 seconds and controllable if possible.

Do you have any suggestions how to pull this off? I have been thinking about a some kind of a 555 timer circuit. I also found this: http://electroschematics.com/5476/timer-light-switch/

I'd like to also add that it would be possible to use the last LED/step in the sequence as a trigger for something. For example with an LDR?

Thank you so much for your kind help. Please try to keep your language as easy as possible since I'm not an engineer, just a hobbyist. I can read schematics and I have built lots of circuits but I don't really understand everything that's happening in there. I'll try my best though

Kind regards,
Anssi

 

I was just experimenting a little and I noticed one more clue. Obviously the link between the last 13th pin in the sequence and the 47k resistor causes the looping manner of the chaser. If I disconnected the link it made the circuit to run the sequence through only once.

After that I was playing around with a momentary switch with the ground connection. It seemed that when I pushed the button (ON) it started the sequence but stopped it immediately when I released the switch (OFF). So I was wondering if I could apply here a circuit that opens and closes the gate for the ground or plus voltage at an adjustable rate.

For example: It takes 3 seconds for the sequence to finish. I would set the voltage gate circuit to open and close the gate every 5 seconds. So when the gate first opens it starts the sequence. After 3 seconds the sequence finishes (and doesn't repeat). The gate is still open for 2 seconds and after that it closes. After 5 seconds of closed gate it opens again and the sequence starts again.

Does this sound possible? Would this be the thing I'm looking for: http://home.cogeco.ca/~rpaisley4/LM555.html#4

 

It looks like this circuit was designed to be infinitely expandable by adding a new 74HCT164 chip with LEDs connected to it like the originals. You would just connect pin 13 of the previous 74HCT164 to pin 1 of the next 74HCT164 and continue adding stages as needed. If you wanted to add some delay where no LEDs were turned on, you would simply remove some led's from the end of the chain. The sequence would continue, but the LEDs wouldn't turn on because they wouldn't be there. If you look at the modified schematic, I added an extra stage and only put four LEDs in the chain. Then I connected pin 11 to the 47k resistor, thereby making it the end of the chain. So the four leds on the last chip will blink in a row, then it will wait two clock ticks, then start up again at beginning of the chain. You can customize this by changing the amount of 74HCT164 chips, the amount of LEDs in a chain (only connect one LED to one pin though) and where to connect the 47k resistor.

That being said, you might run into problems using the 74HCT164 to drive the LEDs directly for this application. It is not meant to drive the amount of current LEDs require and you run the risk of burning out the chips. You can use a transistor to turn on an LED, but you would need one transistor for each LED and that might get expensive and hard to wire up. One LED at a time might not be a problem though. But if you start seeing your chips dying, I'd be willing to bet that that's why

 

Thank you for your reply

Yes that's a nice idea to leave some LEDs out from the end of the sequence. I have actually expanded the circuit with additional 74HCT164 chips already and it works fine (Thanks to Bill Bowden for instructions). But if I'm running the sequence with fast speed it trespasses the final steps too quickly for my purpose. I would like to have at least 1 second of delay. If the sequence of 45 steps lasts for 3 seconds it would mean that by leaving 9 "empty" LEDless steps to the end the delay would last only for 0,6 seconds.

I JUST 5 minutes ago tried to apply the basic astable 555 timer On/Off to the voltage and it worked! I don't have time to draw a complete schematic of this but for those who are interested it was this:
http://home.cogeco.ca/~rpaisley4/LM555Astable.GIF

and the output goes to the sequencers voltage rail. I just got to be careful with the part values.

I'm so excited!

Thanks to newothegreat for his contribution. I appreciate help like this.