# Convert 10 MHz sine wave to 1Hz TTL (PPS)

#### xSkGx

Joined Mar 21, 2011
4
Hi, I have a 10 MHz sine wave and I want to convert it into a 1 Hz square wave.

Wave details:
Vpk-pk: 4V, Cyc RMS: 1.4V, Period: 100ns, Frec: 10 MHz

I found some schematics (this one) but its input is 10 MHz square wave, so if it's easier to convert 10MHz sine to 1 Hz square give me a hint please.

#### bertus

Joined Apr 5, 2008
22,289
Hello,

You can use the circuit if you put an schmitt-trigger in front of it.
An 7414 is an schmitt-trigger that will output the wanted squarewave.

Bertus

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#### t06afre

Joined May 11, 2009
5,934
Using a 7414 is an schmitt-trigger may be an good idea. But asuming 5 volt as supply voltage. The positive-going threshold will be typical 2.38 volt and max 3.15 volt. And also the 7414 will not like negative voltage on the input. This is something that need to be sorted out

#### bertus

Joined Apr 5, 2008
22,289
Hello,

I see no big problems.
Use this circuit as input:

Remove C7 and R2 and R3 to connect it.

Bertus

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#### t06afre

Joined May 11, 2009
5,934
Hello,

I see no big problems.
Use this circuit as input:

Remove C7 and R2 and R3 to connect it.
Yes that will do the job nice

#### RiJoRI

Joined Aug 15, 2007
536
Hi, I have a 10 MHz sine wave and I want to convert it into a 1 Hz square wave.
Just out of curiosity, why would you want to make a divide-by-10-million circuit???

--Rich

#### t06afre

Joined May 11, 2009
5,934
@Bertus
Since we are talking about a relative high frequency here. Do you think it would be an idea to select resistor values. In order to get a better match with the signal generator output resistance. Which I guess is around 50 ohm

#### bertus

Joined Apr 5, 2008
22,289
Hello,

You could put a 50 Ohm resistor on the input to ground for impedance matching.

Bertus

#### Markd77

Joined Sep 7, 2009
2,806
On the schematic I noticed that the supply voltage of 5V is being fed into a 5V regulator. That isn't going to work well, the 7805 regulator would need at least 7V to work reliably.
If the 5V supply is stable anyway you could just skip the regulator.

#### THE_RB

Joined Feb 11, 2008
5,438
You can do it with one tiny PIC like a 12F675 and no other parts needed.

Just use the 10MHz sine to clock the PIC (your 4v p/p signal will be fine) and use firmware to generate the 1 second output.

The firmware is proven and very simple, it is the ZEZJ (Zero Error Zero Jitter) algorithm about 1/3 of the way down this page of PIC timing systems;
http://www.romanblack.com/one_sec.htm

#### xSkGx

Joined Mar 21, 2011
4
@bertus
Then it was that I tought, I need a schmitt-trigger, ty for the schematic.

@t06afre & @bertus
Yes, it's 50Ohm, I forgot to mention it but I'm counting with it.

@RiJoRI
Well, I have an rubidium atomic clock and I need an 1 PPS signal in order to sync my system's clock.

@Markd77
Yes, I have two options, one is to use 5V from the computer's PSU and other is to use 15V from the atomic clock's PSU.