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chrischrischris 03-06-2012 12:23 PM

Count down timer for my soccer club
 
Hi.
I'm trying to make a count down timer for my soccer club. I've got the count down happening with 2 x 7-segment led display, 4510s and 4511s (including a 32Khz crystal).

I'm having difficulty working out how to get the count from 00 to 59. I've put in a preset switch that sets to 59, then it counts down from there. However to automate it when it sees 99 I don't know how to tackle. Please can someone help.

Bill_Marsden 03-06-2012 12:45 PM

1 Attachment(s)
I breadboarded a simple counter that was the heart of a 2 or 3 minute countdown timer. Maybe it can give you a few ideas.

It was on Sheet 3 I believe, been a few years since I worked on it.

elec_mech 03-06-2012 04:49 PM

Hi Chrischrischris, welcome to AAC.

So you press the preset button, the count goes to 59 and immediately starts counting down, correct?

When it reaches 00, it then goes to 99 and begins counting down again, correct?

You want it to go from 00 to 59 automatically?

May I ask why?

I am unsure why you want the clock to count down to 00 then automatically reset to 59 and count down repeatedly.

I designed a similar counter and fed the BCD outputs to an 8-input NOR gate whose output was connected to the reset pin of my clock IC. In that way, the counter stopped at 00 until the preset button was pressed. You could do the same thing but feed the output of the NOR gate to the preset pin. If you use a CD4078, you can select either a high or low output signal depending on the needs of the preset pin. This should force the counter to "reset" to 59 once 00 is reached.

chrischrischris 03-06-2012 08:16 PM

Thanks Bill for the quick reply and the details to your count down timer.
I'm a bit of a novice on my breadboard and self taught. On the weekend I read up on NOR, AND, NAND gates etc to see how the signals were processed in the ICs. Your circuit scares me!

It seems to be on sheet 3 as you said, and "6 counter" I'm trying to figure out. There's an OR gate (I think you've made up out of 2 diodes and a resis, however I think you're using that to reset that digit. Correct? Pin 6, 11 and 14 are they going to multiplexers to obviously combine signals, however I haven't progressed to multiplexers. YO, X1, Mux Qa, Mplx A - bit foreign to me. Could you look at the link http://members.shaw.ca/roma/up-down.html and see if this can be adapted (as this is where I'm at).

chrischrischris 03-06-2012 08:28 PM

Hi Elec_Mech.
Thanks for your reply also.
Yes, when I press my reset button on the breadboard circuit I've made, it resets to 59 and counts down from there (through 2 preset dip switches fed to pins 3,4,12&13 of the 4510s).

Currently I only have 2 digits I'm experimenting with - units and 10s. I've used 2 x 4510s and 2 x 4511s. It's the 4510s I'm fiddling with to try to "repeat count" from 00, 59, 59...01, 00, 59, etc (i.e. the forcing the "tens" to count between 0 and 5). Next I was going to attempt 2 more digits (the minutes - where I need to preset to 45 minutes).

There must be a "conventional way" of forcing one of the 4510s to essentially count from 0 to 5, 4, 3, 2, 1, 0, etc, but I don't know how - I'm trying to re-invent the wheel, and for a novice like me I'm struggling with my ANDs NANDs and NORs! Can you help. I've spend "days" with combinations and googling! I need it simple.

elec_mech 03-06-2012 09:31 PM

Hmm, this is something I'll have to think about and research myself. I've seen clock circuits here that use logic ICs to reset 59 to 00 in the seconds and minutes and 12 to 1 in the hours, so I'm relatively sure something is possible in the reverse.

Allow me to pontificate a bit . . .

chrischrischris 03-06-2012 09:44 PM

Success!!! (I think).

I ended up using a 4025 tripple input. From the 4510 that displays the 10s, I was looking for a 9 in hex - (1,0,0,1) - from pins 6, 11, 14 and 2 respectively. I could use AB&D or AC&D through my 4025 to get a "high" which I would reset the 4510 with the preset (via 2 dip switches).

I used 1 of the 3 gates of the 4025, 3 pins linked together and stuck pin 6 to it (looking for a high to give an output low). I did the same on the 2nd gate with pin 2. I then fed both these to gate 3 as well as pin pin 11 (looking for low). 3 lows make a high! in the NOR gate. Signal sent to my preset on the 10s "load input" which grabs the combination 59 (0101 & 1001) via the 2 connected dip switches. Is this correct?

Can I assume that I can do the same "idea" with the minutes?

elec_mech 03-06-2012 09:50 PM

Could you post a schematic? Much, much easier to understand and we can offer a lot more help with it.

chrischrischris 03-07-2012 02:52 AM

Elec_Mech,
I'll draw up the wiring diagram when I get home today and upload for you to look at what I've done to date...

chrischrischris 03-07-2012 11:25 AM

Schematic
 
1 Attachment(s)
Hi elec_mech (and Bill).

Here is a schematic I've just drawn up for the circuit I've done to date.

Down the track, I'd like to delv further into:
* Changing the 7 segment LEDs to multi leds (maybe 100 per letter)
* How to provide power to the leds (voltage regulators - I'm guessing here)
* How to create a selection switch to pick various preset times - maybe 2 for the minutes
* Resetting the timer and stop start with the timer
* Wireless operation (remote).

Hopefully I can wrack your brain down the track, then provide others with schematics for this project.

Chris circuit.pdf

Thanks in advance.
Chris.


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