Help with clock circuit

[johnsoax]

Hello,

In building my meeting timer (see other thread by me), I found that I need a one second clock. I have a 120VAC to 12Vac transformer, so I would love to be able to steal the 60Hz signal off of it and then step it down to 1Hz. Any ideas? I currently have a zener diode and a 10K resistor across the 12Vac line, but it doesn't seem to work.

 

[mugzzzzy]

hi,

Before u try anything u should ask some one who knows about electronic first....i really recomand that u ask some one...

i didnt read ur other tread but i can help u a bit.... first the 60Hz from the 120AC....its just a sine wave with a 1/60 sec for one period....it has nothing do to with ur timer circuit.... what u need is a crystall oscliator for ur timer circuit... first find the oscilator of ur choice then make a square wave signal using some circutery, then using a chip u make that frequency down to 1Hz ....

and what are u expecting to see when u put the zinor diode and the 10k resistor??

 

[Sebi]

You need frequency dividers One div.by 10, and one div.by 6.
The resistor and zener only make rectangular wawe from sine.

 

[johnsoax]

You need frequency dividers One div.by 10, and one div.by 6.
The resistor and zener only make rectangular wawe from sine.

I have a 6 and 10 counter to be the frequency dividers. I'm having trouble getting the 60Hz to begin with. I have the resistor and the zener tied across the 12Vac transformer, but I'm not coming up with 5.1V, it is more like 8.

 

[Sebi]

Please post Your sematic. I think the problem: need independent winding for clock signal source, or use one-way rectifier.

 

[john1]

or you could use the unit from a discarded quartz clock.
They use next to no current, and are very very accurate.
They give a brief pulse every second.

When i see them in the rubbish,
i generally pick them up.

The plastic parts which work the mechanism
are usually the parts that fail.
Very often they work fine, and maybe they were discarded
because the battery ran down.
I have never come across one that had faulty electronics.

Regards, John

 

[johnsoax]

Please post Your sematic. I think the problem: need independent winding for clock signal source, or use one-way rectifier.

Sebi, that is almost exactly my schematic. I have a full bridge rectifier though.

I may just use a 555 to get a 10Hz clock and then use the counter to step it down to 1Hz (as I need both for my circuit).

I keep hearing people talk about using a watch, but I wouldn't even know where to look.

 

[johnsoax]

The rectifier is not drawn right, but it is installed correctly.

 

[Sebi]

For proper potential of 60Hz, need common GND with DC section. Forget the bridge, use one diode and connect 100k resistor paralel with zener.
Another possible solution:

 

[Russlk]

You can keep the bridge rectifier by using a diode as below:

 

[johnsoax]

You can keep the bridge rectifier by using a diode as below:

I will give that a try tonight, thanks.

 

[ljcox]

Alex,
You will also need a Schmitt Trigger to reduce the rise and fall times of the signal before you apply it to the Modulo 60 counter. Some counters are fussy about the rise and fall times.

Len

 

[johnsoax]

Alex,
You will also need a Schmitt Trigger to reduce the rise and fall times of the signal before you apply it to the Modulo 60 counter. Some counters are fussy about the rise and fall times.

Len

I was going to run it through an invertor. I have an extra schmitt trigger Nand gate on my board right now, I guess that I could use that instead.

 

[ljcox]

[/quote]

I was going to run it through an invertor. I have an extra schmitt trigger Nand gate on my board right now, I guess that I could use that instead.[/quote]

I doubt whether an inverter would make the rise and fall times short enough.

You could use the Hex Schmitt Trigger inverter, 74C14 or 40106, etc. Note that these can be used as normal inverters when the Schmitt action is not necessary.

Len

 

[johnsoax]

It worked like a charm, I just have to change the input to the divide by 6 to 6 and then it worked great.