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Count down tally counter

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bigfish312

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Im looking to build a Decreasing counter. Id like to have a three fig, 7 seg display that will count down from a set, but easily changeable number (450, 300 and 100) and reset back to that number but not when it reaches 0.

I if there is a way of making the display flash when it is nearly at 0 (eg <20) this is also part of my brainstorming.

Thanks in advance for the help
Bigfish
 
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kchriste

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Im looking to build a Decreasing counter. Id like to have a three fig, 7 seg display that will count down from a set, but easily changeable number (450, 300 and 100) and reset back to that number but not when it reaches 0.
While a microcontroller is cheaper, you could still look into counter chips like the 74LS192, 74HC192, etc and interface them with a seven segment driver chip like the 74LS47, 74LS48, etc.
I if there is a way of making the display flash when it is nearly at 0 (eg <20) this is also part of my brainstorming.
At this point I'm strongly saying microcontroller, though it can be done with logic chips but it's a lot of hassle.
 
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shimniok

Member
Seems like microcontroller is the answer to everything these days :D The thing is, if you don't want to futz around with all the overhead of setting up an IDE, getting the programming figured out, etc., then do it in logic. That can be more of a hassle for some. I bet you could even get the flashing going without much trouble... but start with the countdown logic first... happy to help however I can.
 

bigfish312

New Member
firstly, thanks for the quick replyes

I dont think using microcontrolers is an option to me as i dont have the funds to set that sort of thing up.

The second reason for this home grown project was to get me back into using logic as i start my first year on a electronic masters this September. so im interested in the second option. It will be part of a progressive project that is going to be tied into a much larger circuit.

any help or pointers to usefull books or links would be most use full

thanks for your time
Bigfish312
 

bigfish312

New Member
counting rounds fired from a paintball gun, the trigger is eletronic, so i will use the input from there as the count. The different start values are for the mesured capasity hoppers i use, the 100 is for counted speedball games. Firing when there is no ball loaded causes lots of damage so its important you dont, the display will let me know that im not going over the set amount.
 

blueroomelectronics

Well-Known Member
How big do you hope to make the PCB? It's going to take a fair amount of logic to do what you want and if it's TTL it'll be power hungry.
 

shimniok

Member
How much do you already know about logic circuits? If you've done this before, maybe you'd feel comfortable looking up the datasheets for the counters listed above? You could get a sense of what needs to happen at least to count down.

My thought is you'd have one set of circuits to set the initial value. That initial value feeds into the countdown chip / circuits. Another circuit drives the LED 7-segment displays. And another circuit flashes the power to the 7-segment circuits when the counter is < some value. So you can tackle each of these pieces one at a time.

Michael
 

bigfish312

New Member
Im relitvly new to logic, i know the different types of gates but havent done alot of work with them and to be honist im still learning.
The box its planning to go in is fairly large, aprox 60x200x30mm so there is lots of space. The hoppers are powered so i can use the battrie off them (9.6v 1.2Ah) so i can use that as needed.
 
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kchriste

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Since this is going to be a learning experience, you'll need the Pocket Data Book from TI which includes lots of info about the 74 series glue logic all in one PDF. Here is a circuit out of a very old book that you can start from as it is a relatively simple matter to cascade another 2 counters and display drivers for 3 digits. You'll need pullup resistors on pins 9, 10, 1 & 15 of the 74192 especially if you use 74HC series logic but it is good practice even with the 74LS series. You can use your trigger in the place of the 555 pulse generator if it is 5V level. Have fun!
 

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