12mins, 10mins, and 4mins, countdown timer

[ion2557]

I've designed a countdown timer using JK flip-flops with preset and clear. The schematic is posted below. Including the diagram of the clock.





The outputs of the countdown timer, the ones connected to the 7segment LED display, are supposed to be connected to a 74185  Binary-BCD converter IC and would be passed through a CD4511 before the 7segment LED.

The switches for the 12mins, 10mins, and 4mins, are supposed to be pulse switches.

Will someone help me with my clock?

Coz I can't make it to a exactly or near 12mins or any of the settings. I have a difference of about 0.2-1.3seconds delay/advance.

Any comments or suggestions regarding my design is highly appreciated. Thanks.

[motion55]

There is a wide tolerance when using RC circuits for timing. The 1uF capacitor can have a 5% error or worse for an electrolytic cap.

You should use a crystal controlled clock. It seems you are using a 1 second time base. You use a 32768Hz clock crystal oscillator and divide it down to a 1Hz frequency using a CD4040 + one  J-K flip-flop..

[marcelino]

There is a wide tolerance when using RC circuits for timing. The 1uF capacitor can have a 5% error or worse for an electrolytic cap.

You should use a crystal controlled clock. It seems you are using a 1 second time base. You use a 32768Hz clock crystal oscillator and divide it down to a 1Hz frequency using a CD4040 + one  J-K flip-flop..

papano po ang pag-apply ng xtal oscillator sa circuit na tulad nito?

[ion2557]

papano po ang pag-apply ng xtal oscillator sa circuit na tulad nito?

yup..

pno nga po b apply crystal oscillator s gni2ng ckt?

ndi q p kc ntry gumamit ng crystal oscillator eh..

You should use a crystal controlled clock. It seems you are using a 1 second time base. You use a 32768Hz clock crystal oscillator and divide it down to a 1Hz frequency using a CD4040 + one  J-K flip-flop..

ts pano ung division nung CD4040 ng frequency..

idi2vide b nya into 12 equal parts in a linear manner?.

thanks po pla s pgrespond..

[motion55]

The 32768Hz clock has to be divided in 15 stages to get 1Hz. Each stage divides by 2. A CD4060 ripple binary counter happens to have 14 stages and an inverter gate that can be used as oscillator. Checkout the CD4060 datasheet. I earlier said it was CD4040 but the CD4060 seems to be better. You need a 15th stage composed of a J-K flip-flop to divide 2Hz to 1Hz.

http://www.national.com/ds/CD/CD4020BC.pdf#page=1

[ion2557]

thanks sir..


i get it now.

the only problem remaining is that the only available crystal oscillator in our vicinity is around 3.2MHz.

it would then require me to add another CD4060, am i right sir?

[ion2557]

ooppss...


i would like to correct my self..

i need to add an 8-stage Ripple-Carry Binary Counter/Divider and Oscillator if there is one like this available and i should remove the flip-flop stage you have suggested..is there anything like this sir?.

if there is none, then it means that i would create the stages with flip-flops. is it correct?

[ion2557]

thanks sir..


i get it now.

the only problem remaining is that the only available crystal oscillator in our vicinity is around 3.2MHz.

it would then require me to add another CD4060, am i right sir?

that is if it is possible to get an output to the 8th stage of the CD4060.