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### Author Topic: My clock design sucks  (Read 6651 times)

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#### Beatle

• Guest
##### My clock design sucks
« on: September 02, 2008, 22:59:10 PM »
I might have done something really stupid here but i am amateur.

I want to make a clock. I managed to make one using cmos to drive 7seg displays. Also, cmos are used fof BCD counters. Until here ok. I think i have done the stupid thing with the timer. I used 555 timer and calculate to 1Hz. I run some tests before, for example put it to work for 1 hour, and adjust it, and agai and again, but i never manage to have good accuracy.

And the strange is that, the accuracy may change without i change anything. It may show time forward (in one day) or time backward !!!

I want to use crystals but i cannot find crystals 1Hz. I thought of 10Khz crystals and use dividers, but use for example 4 dividers by 10? Is this normal?
What would be a normal operation?

#### Supernova

• Full Member
• Posts: 149
##### Re: My clock design sucks
« Reply #1 on: September 03, 2008, 10:41:57 AM »
If you want accuracy, you might consider an even higher crystal like a 32.768kHz and divide by 256 and 128 and you get 1 Hz using 2 TTLs. You might also consider software division using microcontroller

#### kammenos

• Guest
##### Re: My clock design sucks
« Reply #2 on: September 03, 2008, 18:16:13 PM »
I might have done something really stupid here but i am amateur.

I want to make a clock. I managed to make one using cmos to drive 7seg displays. Also, cmos are used fof BCD counters. Until here ok. I think i have done the stupid thing with the timer. I used 555 timer and calculate to 1Hz. I run some tests before, for example put it to work for 1 hour, and adjust it, and agai and again, but i never manage to have good accuracy.

And the strange is that, the accuracy may change without i change anything. It may show time forward (in one day) or time backward !!!

I want to use crystals but i cannot find crystals 1Hz. I thought of 10Khz crystals and use dividers, but use for example 4 dividers by 10? Is this normal?
What would be a normal operation?

555 will not have any accuracy. First of all, the oscillation depends on the resistors and capacitors, thet lack of accuracy. Also, it is very sensitive to temperature changes. Thus, you will go faster during summer and slower during winter... You may not like this.

#### Beatle

• Guest
##### Re: My clock design sucks
« Reply #3 on: September 05, 2008, 19:16:14 PM »
If you want accuracy, you might consider an even higher crystal like a 32.768kHz and divide by 256 and 128 and you get 1 Hz using 2 TTLs. You might also consider software division using microcontroller

Can you give me an example. Sorry if i suck but i am amateur noob.
How to make 256 and 128 division? How many chips must i use? And what is this software division?
Iam sorry that i do not understand
And very thank for the help friends

#### Supernova

• Full Member
• Posts: 149
##### Re: My clock design sucks
« Reply #4 on: September 07, 2008, 10:14:05 AM »
I suppose that software division he means with μController. And i also suppose that you do not have any idea how to use micros.

The most simple solution is to use the 4040. This can give you up to 1/4096 division. Here sre the pinouts: CMOS 4040 Pin out.

You may use 2 4040 chips cascaded to achieve up to 16777216 division!!!

If for example you want 256 and 128 division (as mentioned before), you will put your 32.768kHz crystal oscillator output to the /CLK
input of the 1st 4040. Then you will connect the output Q7 of the 1st 4040 to the /CLK input of the 2nd 4040. The 1Hz oscillation is now taken from the Q6 output of the 2nd 4040.
You may also consider using higher crystals for oscillation. Keep in mind that the faster the crystal, the better the accuracy you will have. But you have limitation of the 1st divider chip you use. If you use for example High speed CMOS, limitation is 60MHz.

#### Beatle

• Guest
##### Re: My clock design sucks
« Reply #5 on: September 10, 2008, 08:04:43 AM »
Thank you for the help friend. I will change it!