Ive searched the internet and checked some old circuit books around but I cant seem to find a circuit to do what I want. Basically it needs to:

1. Set a 7-seg display to show up 10 when powered on
2. Count down from 10 when a certain switch is closed/pressed
3. When the timer hits zero, the display stays at zero and fires a one-shot
4. This one-shot triggers a relay on and off, preferably with it on only for about 1-2 seconds

It will be reset by having the power cycled. In case youre wondering, its for a switchboard to launch small explosives. Thanks for your input.

 

dump the search for any standard circuit. just use a simple micro , a single chip will do all u want to do

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Incredible !ndia

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"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

I know this seems obvious, but I often look over simple details in complex problems.

Don't forget to display 10, your going to need two seven-seg displays.

 

Yup I know, or a two-digit display. Can you give me a site that would least have examples of PIC code and I could go from there? Ive never done work with microcontrollers before. Also, would it be possible to set up a virtual microcontroller on the computer and simulate circuits and code with it? And would I be looking at a 16F84, 16F873 etc?

 

http://winpicprog.co.uk/pic_tutorial.htm
piclist.com

__________________
Gods own Country
Incredible !ndia

www.flickr.com/photos/_akg/

"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

Anyone interested in writing a bit of code to do that for me? Im having a hard time learning PIC code, as with any other code that Ive tried to learn. Or even just a simple countdown from 10 circuit that I could play around with.

 

how much are you willing to pay for it?

__________________
Gods own Country
Incredible !ndia

www.flickr.com/photos/_akg/

"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

If you'd looked at my tutorials you would have noticed that they include all the parts you require, and just need putting together as you wish. The 7 segment tutorial should be of particular use to you?, as it counts up on two 7 segment displays.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I looked at them, but the problem is that I dont understand any PIC code at all, and since we're coming up to exams very soon, I dont have a lot of time to try and learn it. Mind you, the timer is kind of a side project, but Id still like to have it around in the summer.

 

Paul Obrien

A discreet solution, try a 4017 decade counter driven by a 555 with the LEDs mapped by diode arrays OR an EPROM . I'd rather use a PIC or 89c2051.

 

Forrest Mims had a circuit in his Engineer’s Notebook II (25 years old) that does exactly what you want with a 74LS192 BCD up down counter and a 74LS47 common anode display driver. The borrow pin could fire your explosives. Try a search for 74LS192 and 74LS193 4 bit counter circuits. If you don’t find what you want, let me know. I will scan it for you.

 

That would be extremely helpful if you scanned it.

 

Looks like what I need. All I have to do is set the astable 555 to 1Hz and play around with the switches and it should be good to go right?

EDIT after some reading about timebases, would I be able to omit the 555 and use a 4060 with a 32.768MHz crystal, followed by a 4013 flip flop to get a 1Hz pulse and just feed the 7400 with that?

 

Either way should work. 555s do change frequency some with temperature changes, especially at low frequencies.

 

Its going to be used outdoors, but it doesnt have to be EXACTLY one second per pulse, its just kind of a 'for effects' thing. I think Im just gonna stick with a 555 since I dont have an xtal. Anyone have those chips in the circuit? I cant seem to find them in my stash and I cant get them as samples from TI for some reason.