Square wave frequency doubler

[stitch67]

I realise a similar topic has been posted before (and I have viewed some earlier forums) but I want to add my specifics and requirements with the hope that someone can reply with a simple and effective solution or circuit diagram. Please go easy on the tech jargon as this is all new but I am willing to give it a go.
I have a device which transmits a square wave signal within the frequency range from 1Hz to 700Hz (highly variable frequencies). I want to double the frequency value before sending it to meter. Another requirement is that I would prefer it if possible for the circuit to work with 12VDC without the need to transform to another voltage.

Regards
Stitch

 

[Roff]

I realise a similar topic has been posted before (and I have viewed some earlier forums) but I want to add my specifics and requirements with the hope that someone can reply with a simple and effective solution or circuit diagram. Please go easy on the tech jargon as this is all new but I am willing to give it a go.
I have a device which transmits a square wave signal within the frequency range from 1Hz to 700Hz (highly variable frequencies). I want to double the frequency value before sending it to meter. Another requirement is that I would prefer it if possible for the circuit to work with 12VDC without the need to transform to another voltage.

Regards
Stitch

It's easy if you don't need a 50% duty cycle at all frequencies. If you do, it's a lot more difficult.
What is the amplitude of your signal?

 

[stitch67]

I have the specs on the instrument being measured - it is an anemometer that has an optical sensor which when the wind cups rotate, a disc with a"square wave" like cutting blocks the sensor switching it on and off and this gives the varying freq signal in what I would say is very nearly 50% duty cycle.
_________________
__ __ __
__| |__| |__| |__ <----- light sensor sits at this level and switches on/off as this disc with the square wave outer rim spins around.

If the wind speed is constant then it would be 50% but as the wind gusts vary, the frequency output varies and I would assume the cycle duty would vary gradually. If there is no wind, the signal would remain in either a high or low state, if this complicates things. Sorry about being too verbose, but I'm trying to give you a visual picture off what I am trying to achieve.

Instrument specs (only info I have available from manufacturer's specs)

Property Description/Value
Sensor/Transducer type: Cup anemometer/Opto-chopper
Measuring range: 0.4 ... 75 m/s
Transducer output: 0 ... 75 m/s
Characteristic Transfer Function: 0 ... 750 Hz square wave
Uf = 0.1007 × R + 0.3278 (Uf = wind speed; R = o/p pulse rate)
Accuracy (within 0.4 ...60 m/s)
With Characteristic Transfer Function: ± 0.17 m/s*s
With "simple transfer function" Uf = 0.1 × R: ± 0.5 m/s
Transducer output level:
(Iout < +5 mA): High state > Uin -1.5 V
(Iout > -5 mA): Low state < 2.0 V
Settling time after power turn-on: < 30 µs
Operating power supply 9.5 ... 15.5 VDC, 20 mA typical

Regards
Stitch

 

[Roff]

But why do you want to double the frequency? Knowing the application will help us help you.
The question I asked was, do you need a 50% output duty cycle.

 

[stitch67]

There is a second option if this is easier though it means losing a decimal point in accuracy when displaying the wind speed.
That is reducing the frequency by a factor of 5. Found this site
**broken link removed**
if you can help me with some suggestions if this approach will work and is simpler than doubling I would be appreciative. Regards Stitch

 

[stitch67]

Ron, the instrument measures frequency in metres/sec. That is 30Hz = 30 m/s. I want to display the value as knots (to use on my yacht) which is very close to doubling.
Ie, 30 Hz= 30 m/s = 58 knots
the display unit I intend to purchase is on ebay
**broken link removed**

Just trying to rig up something simple but useful.
Hope this helps with my request.

Stitch

 

[stitch67]

Ron, the instrument measures frequency in metres/sec. That is 30Hz = 30 m/s. I want to display the value as knots (to use on my yacht) which is very close to doubling.
Ie, 30 Hz= 30 m/s = 58 knots
the display unit I intend to purchase is on ebay
**broken link removed**

Just trying to rig up something simple but useful.
Hope this helps with my request.

There is a second option if this is easier though it means losing a decimal point in accuracy when displaying the wind speed.
That is reducing the frequency by a factor of 5. Found this site
**broken link removed**
if you can help me with some suggestions if this approach will work and is simpler than doubling I would be appreciative.

Regards Stitch

 

[audioguru]

Remember car speedometers with red seven-segment LED displays in the 70's?
You couldn't see them in the daytime. At night the numbers kept changing and were a blur.
You want that on your yacht?

A moving pointer is easily seen and can be lighted at night.

 

[Leftyretro]

Remember car speedometers with red seven-segment LED displays in the 70's?
You couldn't see them in the daytime. At night the numbers kept changing and were a blur.
You want that on your yacht?

A moving pointer is easily seen and can be lighted at night.

Yea they sucked, at least on my '86 T-bird it did. Also update rate was pretty slow. Also the speed number would stop at 85mph even though it would go much faster

However I loved that car until it's demise after 175K miles (gross polluter status, calif smog laws), probably the last V-8 I will ever own.

My Buick (2000 LaSabre V-6) has analog display for both speed and RPM, but of course they are first digital processed and then analog driven, because there is a MPH/KPH switch and you can make the speed display change instantly between those units, makes the needle jump

On a side note, this buick was the first car I had with a low tire inflation alarm. When I had first to change a tire I looked for a sensor to figure out how they did it, but could find anything. I googled and found out there are two different systems. A more expensive one used pressure sensors and is mostly used in large semi trucks. For cars, most just use the existing anti-locking brake speed sensor. It looks for a difference between the four wheel speeds for one different then the other three, pretty cleaver. It's effective because I got a low tire pressure alarm once but couldn't visual tell which tire, but measured 20 psi in one and the other 3 were at 30psi. Anyway this system doesn't display which tire is low, but does tell you that there is one different then the rest.

Lefty

 

[Roff]

OK, here's a schematic. I agonized over the voltage regulator. The counter datasheet says it draws 500mA, and with the boat's battery at 14V (charging), the maximum dissipation of the 7805 will be 4.5W. However, I'm sure that's with all 28 LED segments lit. Normally, that will never happen. Still, you should have a husky heat sink on it. I considered specifying a switching regulator, which would be much more efficient, but a canned one is harder for me to find (maybe one of the other guys knows of one), and I didn't want to design one. If you go with the 7805, I'm still not sure of a part number for the heat sink. Again, maybe one of the other guys can chime in.