I'm looking to make a small clock - I have everything planned except the timer circuit. I need to find two circuits: one that will send its output high every second and one that will send its output high every 60 seconds (I haven't decided whether or not to include seconds yet!).
I was thinking something with the NE555 timer but so far I cant find the right resistor/capacitor values to make the time period exactly 1 or 60 seconds.
I implemented a divider with two CD4017 Johnson counters giving a 1 sec pulse. The signal induced in a small wire acting as an antenna in the input was taking it from the 50 Hz in the wiring nearby.
Perhaps too bulky for you.
Have you dismantled a table clcok? Lots of them come with small xtals and the divider already giving 1 Hz output.
Without knowing what a 4040 is (and without looking it up) if you properly divide by those two numbers it should be as accurate as the crystal. Thats the general way to get a 1Hz frequency. Use a 32768 and divide it down.
As mentioned before, you can also use a 0 crossing from mains power and divide that down.
You've got the right idea. It would be as accurate as the crystal specifications once you've tuned it. 32,768 Hz crystals are used all the time in battery powered clocks.
The 32k crystal idea is a good idea i think, but they do make single chip
solutions to divide this down to 1Hz. This chip has all the counters in
that one chip.
If someone wants to look this up that would be great, or else i'll have to
check to find the part number.
The 32k crystal idea is a good idea i think, but they do make single chip
solutions to divide this down to 1Hz. This chip has all the counters in
that one chip.
If someone wants to look this up that would be great, or else i'll have to
check to find the part number.
I'm going to go with the CMOS 4060 & 4040 with the 32.768 kHz crystal purely because of the range of part available at my local supplier of these parts.
I think so, it's been so long now since i looked at these circuits.
For one reference i used a crystal osc in DIP package connected
to a divider (large divide ability) and so i didnt have to play with
the oscillator section at all. Two chips basically.
Frosty:
What kind of accuracy do you need? I ask this because you
may not need a crystal controlled oscillator just an RC type
which is a little easier to do.
I think so, it's been so long now since i looked at these circuits.
For one reference i used a crystal osc in DIP package connected
to a divider (large divide ability) and so i didnt have to play with
the oscillator section at all. Two chips basically.
You'd need an oscillator for the crystal. Use the 4060 for the first stage as it has a built in oscillator.
You've got the right idea. It would be as accurate as the crystal specifications once you've tuned it. 32,768 Hz crystals are used all the time in battery powered clocks.
do you have any experience how much the crystal frequency can be changed using the cap values given in your example?
We have a member in a German forum who wants 720 pulses within a 24 hour time period. This would mean a frequency of 0.008333Hz, almost impossible with a any crystal and divider.
Having the crystal with the nominal frequency the achieved closest result would be 0.0078125Hz using a 14 bit binary counter and another one with Q8 as output.
We have a member in a German forum who wants 720 pulses within a 24 hour time period. This would mean a frequency of 0.008333Hz, almost impossible with a any crystal and divider.
And not too difficult with any microcontroller, I was using 74HCT161s and noticed in the TI datasheet they were discontinued by TI. More and more 74 & 40 series ICs are becoming scarce.
We have a member in a German forum who wants 720 pulses within a 24 hour time period. This would mean a frequency of 0.008333Hz, almost impossible with a any crystal and divider.
It's been a long time since I've used that chip. It really depends on the crystal type and cut. Overtone SC cut crystals can't be tuned very far off. AT cut crystals can be pulled further off than SC cut crystals.
It looks like Diver300 has the correct solution for you anyway.