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  #1  
Old 09-18-2011, 10:30 AM
brozizds brozizds is offline
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Default LED count down timer

Howdy,
I tried to get help with an old project but got no responce. So here is my new one. I would like to diy a varible count down timer on a PCB with a green LED at the start of the timer and a red LED and piezo buzzer at the finish. An LED numeral timer would be great! Times would vary on different timers from 15 min. to 12 hrs. may be. Can anyone help with this or am I asking to much? I apppreciate all your help in the past and on this one!
Thanks Jim
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Old 09-18-2011, 01:28 PM
elec_mech elec_mech is offline
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Hi Jim,

Bertus replied to your other post. I saw it, but I wasn't sure what you were asking for - another circuit design or PCB design help?

In response to this post, what you're asking for isn't difficult. If you have microcontroller experience, that is the way to go to reduce parts count, cost, assembly time, etc. Assuming you don't want to go with a microcontroller, you can do this completely with digital ICs.

The link Bertus sent in response to your earlier post is helpful. Using the same IC, here is another circuit by Bill: http://forum.allaboutcircuits.com/sh...2&postcount=12.

Adding digits to display the time isn't hard, but it will add a lot of hardware to your circuit. Are you looking to display only hours and minutes or seconds too? HH:MM (four digits) vs HH:MM:SS (six digits)?

How big do you want the digits? You can go with the readily available 7-segment displays from 0.30" high to 5" high or make the digits as big as you want using individual LEDs mounted to a plastic board.

Do you want the green LED to stay on until the end of the timing cycle when the red LED and buzzer go off or only for a second or two when the timer is first started?
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Old 09-18-2011, 04:28 PM
brozizds brozizds is offline
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Default timer

Thanks elec mech for the reply and I just saw bertus's reply TY. I would love to get a PCB design for this circuit http://forum.allaboutcircuits.com/sh...0&postcount=27 which works great and was developed by Bill M. I have butlt 8 or so of these but hard wired all and it took very long hence the reason for PCB. But I am open for sugestions. I got interested in possibly led numeral after a pm with Bill. I like the above design because parts are easy to get and not to complicated to build.(freebie for wifes brother)and I think could be fit onto a small PCB. Thank You Again, Jim (the newbie)
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Old 09-18-2011, 06:11 PM
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Bill_Marsden Bill_Marsden is offline
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I'm thinking of designing a simple LED numerical count down timer. I think I hear the sounds of a Guinea pig! Interested?

It isn't too complex, around 7 chips or so. I actually designed and tested a prototype for a stadium timer almost 10 years ago, we regularly get requests for instructions from other folks on the site (students).

Since you are into carpentry you would also have some fun with the box, large LED displays are practical from discrete LEDs.

I'll draw complete plans, you build it, and we'll post it on the complete projects if it turns out to be worth something. I have most of the parts you'll need, so other than labor it shouldn't be that expensive.

First of all, lets define what you need. My concept was for a martial arts timer, which can count down from 3, 2, or 1 minute, has a start, pause, and reset button, and a buzzer when it hits end of count. An additional option is a light bulb on the top of the box.

What is it you are needing?

I think I missed your other post.
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Old 09-18-2011, 07:03 PM
brozizds brozizds is offline
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howdy Bill,
Yepper I'm interested and thanks. These timers would be simalar to our original http://forum.allaboutcircuits.com/sh...0&postcount=27 same purpose for cooking. The 8 I did are still up and running. Now I need about 8 more for the baking area but as in my first thread I would like them to be variable. Is this possible? From a few mins. to possibly 12 or so hrs. But there will be 8 so I can make #1 timer from 5 to 15 mins. #2 timer from 10 to 20 mins. and so on. What do you think ? and can we squeeze it on a fairly small PCB?
Thanks Jim
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Old 09-18-2011, 07:18 PM
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Count down either involve a PIC (which is small) or discrete logic (which isn't).

A really simple way to do it is a pot with a calibrated numbers in back of it. Being analog (as were your other timers) it won't be extremely accurate. Another way is a rotary switch, with 8 positions. These would be small, and a PCB would be super simple, most of the work for these kinds of circuits is in the case, the box they are packaged it. You probably have figured that out though.

I'm willing to help how I can whatever you choose to do. I can't be of much help with the PIC or Arduino, since I have never worked with them, and software is hard work (for me at least). In this I am fossil, I like the old ways.

The chip count I gave could be more for a numerical display, so it looks like you probably don't want to go that route. You might want to try one, but this is going to be a bit of work, and if the 555 route works (with improved controls) then we can go that path.

Something we could do with the 555 is a bargraph, a analog type display that will show percentage of time passed. It will take one or two extra chips, but it would be almost as good as a numerical display. It would be pretty small overall too.
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Old 09-18-2011, 08:43 PM
brozizds brozizds is offline
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thanks im not really looking for super accurate and I do like the pot for adjusting like the last ones with green led on at start and while running and red led with piezo buzzer at the end and could we have the piezo pulse with the red led so the sound is diff than the others I built?
Thanks Jim How bout the PCB layout would that be a problem?
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Old 09-18-2011, 09:45 PM
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For this making a PCB is easy. Now we are discussing features. For some reason this is the longest phase (basically a combination of negotiation and trying to understand someone elses thought processes). It is also where things go wrong generally.

I know you are helping a barbecue place (a family thing). If the people can be trusted to set the knob right this would be simplest way. If not then you are better off with switches, it is hard to screw up turning something on or off. Either way the front panel will take up much more space than the circuit inside. A good exercise at this point is to start doodling what you want it to look like.

I know of some nifty way to make labels, which will come in handy later.

Is the bargraph still on, or is it off the project?
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  #9  
Old 09-18-2011, 11:41 PM
brozizds brozizds is offline
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Bill,
thanks I really need a PCB layout for our original timers cause I have 8 more to build. I would be ok with those timers. I've been having probs with my comp. TY jim
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Old 09-19-2011, 12:44 PM
elec_mech elec_mech is offline
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Jim,

If you only need eight boards, I'd recommend using a prototype board. See my reply, post #3, in your original post: http://forum.allaboutcircuits.com/sh...ad.php?t=59475.

No need for the time and expense to design a custom board. All you need is the prototype board (~$3 per board, ~$1-1.50 per circuit), your parts, and solid 22 AWG wire (insulated being ideal, but you can go without as well since none of the jumpers cross each other). If you get the board from RadioShack, you can pick up a three pack (different colors) of 22AWG solid for under $8, P/N: 278-1221 if you don't already have some. I'm reasonably sure elexp.com also sells solid 22AWG too. Then you just need a soldering iron and solder.
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