Minutes Clock + 555circuit

[cloud@PT]

Just Minutes Clock Countdown

Hi Guys

I need your help on a project i have for a timer that look's like a chess clock, but not the same.

I need a Master Timer that count's donw minuts from 99 to 0, in the end it will freeze the TimerA and TimerB.

TimerA and TimerB are the clock's of Team A and Team B, each one is going to turn on their clock, when present (almost like in chess)

It's a simple circuit but I need help on making 555 circuit to give 1 minut clock to the DM74LS90N.

What should i use for the 7led display? and what type of display comon catode or comon anode?

I'm tring to figure it out on the net but all i get is hour + minuts + seconds clock's, i just need the minuts

 

[ljcox]

Did you do a search of this forum for Timer?

I designed a timer similar to your description about 3 years ago.

So if you search for ljcox and timer you should find it.

 

[cloud@PT]

tried, seen a lot but not what i wanted!!

what resistor and capacitor should i use to make the 555 give me minute to minute impulse?

 

[philba]

if you need accuracy for timing, I would not use a 555. rather, I'd use a watch crystal and a 4060 (or 74HC4060)+flipflop+bcd counters to get to minute counting. You could adjust the 555 somewhat accurately but you will get much much better long term accuracy with a 32768 hz watch crystal and no adjustment needed.

 

[cloud@PT]

well the clock is to be used on 20 minut matches between team a and team b, there's no need for a quartz clock or anything like it because there will be no long term counting!

Does anyone have the 555 circuit for minuts? with the value of the capacitor and resistor?

 

[philba]

how would the teams feel if they were getting 19:20 instead of 20:00? a quartz crystal will cost well less than a dollar and need no adjusting.

look at the 555 datasheet for the formulas.

 

[Hero999]

how would the teams feel if they were getting 19:20 instead of 20:00?

You'd be doing very will to get that degree of acuracy. The large value electrolytic capacitor required for a delay of this lengh would have a high tolerance, typically +-20% so at the worst one team might have 16:00 while another might have 24:00.

However I do unserstand that you'll be using the same clock for each team so it probably won't be as bad as this but the drift due to temperature fluctuation and aging of the componants will be significant.

Does anyone have the 555 circuit for minuts? with the value of the capacitor and resistor?

Look at the datasheet, you'll find that T = 1.1RC, study the graphs, rearange the formula for R, then C and plug different values into it until you get the value of T you desire. Having said this you'll need a trimmer pot for adjustment due to the componant tolerances.

But seriously this is not a good way of making a acurate delay, for that checkout this thread. Here's my favourite schematic, it doesn't get much simpler than this, one IC with a crystal and a couple of resistors and capacitors gives you an acurate 1Hz time base, the other taps on the IC will also give you longer delays.

 

[cloud@PT]

well if you say that the 555 will not help to have the time right for the teams, i apreciated, that way i would not be hanged!

The quartz circuit provides the 1hz = 1 second clock.

Since i'm making it only in minuts, and since in normal clocks the minutes part takes the clock after the seconds part, what frequency should i have on my minute timer?

 

[Hero999]

Figure it out yourself.

Hint: 1Hz is one cycle per second.

 

[cloud@PT]

60hz?

I'm going to the store and try to find that quartz clock and the rest of the stuff, nothing like testing!

thanks for the help! keep helping

 

[philba]

no no no. you won't find such a beast. you will need to make one. use a watch crystal - 32768 hz. use a 74HC4020 (14 bit counter with oscillator support) to generate a 4 hz clock rate. Take the output from Qm (pin 2). Then input that into a second '4020 to count by 240. Use a quad input nand gate (74HC20) to look for 240 (000000011110000) on the output of the 2nd '4020. hook up the inputs to Q4-Q7. when the output of the '20 goes low, one minute has passed. It will be low for 1/4 of a second. edit: use the 1 minute clock to reset the second '4020, also.

Use the minutes clock to drive a bcd counters like the cd4510 and into a 7 segment drivers like the cd4511.

total cost? maybe 3 dollars.

edit: arg... got my counters mixedup. use 74HC4060 and not the '4020. sorry.

 

[ljcox]

tried, seen a lot but not what i wanted!!

what resistor and capacitor should i use to make the 555 give me minute to minute impulse?

Was there one that you could adapt to ypour purpose?

I learnt electronics partly by building circuits designed by others and working out how they work. Then I adapted other circuits to meet my needs.

Finally I started designing my own from scratch.

(Later I did a degree in Electronic Engineering)

 

[Hero999]

60hz?

No, wrong way round. 1Hz is one cycle per second, two cycles per second is 2Hz and two seconds per cycle is 0.5Hz, therefore 60 seconds per cycle is 1/60Hz.

Anyway liston to philba, using a 32768Hz crystal with a counter string to divide the frequency down to 1/60Hz is the best way of doing this.

 

[cloud@PT]

well

the problem is that if this problem was 10 years ago i wouldn't be bugging everyone here, and consult the books, the teachers and test it all in the electronics school...

But the world became telecom's for me and no more electronics, but since i have a problem and there is no clock that fit's for this task, i'll construct it!

I'll have a meeting in my school to use the lab and design the circuit, choose the parts, buy them, teste them and if ok i'll give feedback here!

Thanks to all!

 

[Hero999]

Perhaps you could print off this thread and show it to them, they'll probably know exactly how to implement this.

 

[cloud@PT]

The funny thing is that this "product" is for the National Paintball Association I preside, and they will do this project in class, to teach counter's for the students!

It wasn't my decision, the school liked it and it's a really good ideia, there's nothing like doing real projects than to just make one that has no use in real life!!!

I've printed some circuit's you've made, i'll use some part's of it, but it helped a lot just to put my head running a bit like 10 years ago!

 

[RODALCO]

If you use the mains frequency 50 or 60 Hz from the low voltage side of a transformer, put it through a schmitt trigger like a 7413 to give it a square wave to trigger the 7490 or other divider ic's and get your 1 Hz time base.
This can be further divided as required to obtain longer accurate time intervals if you don't want to use a crystal oscillator.
Then if you only want to record minutes then add driver ic's and 7 segment displays as required on the appropiate ic's of the counting chain.

 

[ljcox]

If you use the mains frequency 50 or 60 Hz from the low voltage side of a transformer, put it through a schmitt trigger like a 7413 to give it a square wave to trigger the 7490 or other divider ic's and get your 1 Hz time base.
This can be further divided as required to obtain longer accurate time intervals if you don't want to use a crystal oscillator.
Then if you only want to record minutes then add driver ic's and 7 segment displays as required on the appropiate ic's of the counting chain.

He means 7414 not 7413.

I would use CMOS as it is easier to use and operates over a wider supply voltage range than TTL. It is also more immune to noise.

 

[RODALCO]

7413 is a double schmitt trigger with 4 imput ports per gate, you can leave one port open to allowe for remote start stop options.
For continuous operations put all 4 inputs together.

A 7414 is a hex schmitt trigger with one input per gate.