From 1MHz to 1HZ clock

[RDL2004]

Hi,

I need a simple 1Hz clock signal for a circuit I'm playing with. It needs to be very accurate. I have a 1MHz 100ppm (TTL level) crystal oscillator. What would be a good way to get to 1Hz from there? I don't have to use this oscillator, I just happen to have it on hand. How would you do it?

Thanks

 

[hjames]

If you need *real* accuracy, use a "32KHz" clock - it has better timing characteristics, and is easier to divide down to 1Hz. In either case, a microcontroller is the easiest way of building it, but you can use some discrete counter chips if you really want to do it in hardware.

 

[RDL2004]

Yes, you are right about the microcontroller, I probably should have said that I'd prefer to do this in "hardware". Maybe I should try looking for a non-surface mount 32KHz oscillator.

 

[philba]

Yes, you are right about the microcontroller, I probably should have said that I'd prefer to do this in "hardware". Maybe I should try looking for a non-surface mount 32KHz oscillator.

or make one with a 20 ppm crystal and 4060 + a flipflop. the 4060 14 stage divider gets you almost there (2 hz) and then the ff takes you the rest of the way. all in TH components. total cost well less than $2. if you need 74xx logic, there is a 74HC4060

 

[hjames]

Incidentally, it looks like most RTC chips have some sort of "Square Wave Output" pin where they can output a divided down clock signal. Unfortunately there needs to be something that talks I2C in order to configure it. The main benefit is that RTC clocks have most of the oscillator circuit prebuilt - just supply the crystal.

 

[philba]

good point! though I'm not aware of a small rtc that doesn't require a some sort of processor to initialize it.

by the way, the 4060 does support a crystal directly (plus a couple of caps and resistors).

 

[RDL2004]

I'm not real sure because I'm at work, but I think I have some 4060s. I may also have a couple of 32.768KHz crystals of some kind that I got for a project I thought about doing last year with a Basic Stamp and one of the DS13xx chips. I really wanted to try and use that 1MHz oscillator though, because it works well on the breadboard and I'm not sure a crystal will.

- Rick