Cheap panel mountable frequency counter

[factus10]

This came up on Hacked Gadgets today:
http://nuxieshop.com/forums.html?main_page=product_info&cPath=2&products_id=5

I've ordered one. At $20, it's kind of hard to go wrong.

[gubbeper]

Nice! Let us know if it's any good!

[goodrevdoc]

Wow! this is great. I was just looking around today for one of these. Planning to make a combination voltage input/freq. counter on the output for tuning VCO's. I found some solutions here and there, but nothing as cheap and easy as this. And you get to build it too. I'm ordering one!
-justin

[urbanscallywag]

<nitpick>

That's not a frequency counter! Frequency has a rate and a direction. How are you supposed to measure negative frequencies?

</nitpick>

A "real" frequency measuring device (not what is more commonly known as a frequency counter, a "problem" started by HP I've heard) requires an IQ detector. That way you can measure the direction as well as repetition rate of the input signal. This is just something they cover in school to emphasize negative frequencies.

This project does seem neat if works as advertised.

What may be even cooler would a "real" frequency measurement of a through zero oscillator.

[nuxie1]

Just saw this forum come up in my server logs. Just thought I'd come and say hello, and thanks for the interest. Unfortunately I've had to raise the discounted price to $24 due to extra costs in shipping and packaging and an unstable aussie dollar.

You're right in that its not a true frequency counter, the microcontroller is simple counting rising edges each second and displaying a frequency based on that. However for the price I think it is quite useful for many frequency display applications.

For those who have bought one (or more), please let me know how you find it either here or by emailing me directly. I welcome any feedback. And I'd love to see it mounted and used with other equipment, make sure to post up some photos are email me with them!

Cheers.

[factus10]

If you want to make this a 'true' frequency counter it'd be relative simple to front-end it with a zero crossing detector. You'd need to touch the counting code since most zero crossing detectors put out a pulse for both transitions (pos to neg, neg to pos). Or just divide what the display shows by 2.

Actually, this circuit might do the trick easily.

[urbanscallywag]

Hello nuxie1,

Unfortunately a very large portion of people, even a large portion of engineers wouldn't think twice about calling this a frequency measuring device, so that's why I had to turn on nitpick mode.

I was wondering how well the repetition counter works as SNR decreases. Do you get multiple triggers from noise? I guess this is a question to ask someone who builds this into their modular.

[urbanscallywag]

[nuxie1]

[factus10]

[BananaPlug]

Anybody know how wide the 16x2 display is?

[urbanscallywag]

[nuxie1]

[guitarfool]

[urbanscallywag]

[Scott Stites]

I like a good nitpick as much as the next guy, but obviously in a very practical sense, this is a frequency counter. It's practical in the same sense that referring to most synth VCOs as an oscillator is not technically correct either. People generally get what you're talking about, as opposed to being totally confused when you start pointing stuff like that out.

I can't imagine the response I would elicit at work if I started declaring that the device on my bench and the device my company manufactures really isn't a frequency counter.

"The SINAD meter isn't working with today's build. I should have 40 dB, but it's near zero."

"Are you sure? What's your notch frequency?"

"1 kHz".

"What's your counter read?"

"My what?"

"Your counter".

"I don't know. I don't have one. I could let you know the number of accumulated events per second, however".

"Uhh..."

"But, sadly, not the direction".

"Is there anybody else there besides you?"

We do, however, call our function generators "function generators" and our oscillators "oscillators", though generic tissue paper is often mistaken as "Kleenex".

Cool project, BTW.

[urbanscallywag]

You will have a hard time explaining single sideband modulation without negative frequencies.

Like I said I pointed it out because its emphasized in school once complex modulation is commonplace. Just because many people call a device a frequency counter (again apparently this was an error on the part of HP many years ago) doesn't mean its correct.

Good enough for rock'n'roll? Certainly.

[Scott Stites]

I'd have to agree to disagree, then. We cover complex modulation in the same box (DMR, P25, Tetra protocols as well as arbitrary waveforms and modulation, LSM, C4FM, QPSK, things of that nature) in addition to the standard analog functions such as FM, AM and its cousins, USB and LSB. Rarely, if ever, do we discuss "negative frequencies", or use "frequency counters" to measure the quality, accuracy and purity of complex signals. There are meters, eye and constellation diagrams and plots built in (and built for) specifically those purposes. For sideband measurments, generally I'll use a spectrum analyzer to measure the frequency of a side band, upper or lower, or, for more accuracy, set the receiver to the frequency of the suppressed carrier and measure the error, which should tranlate to the modulating frequency plus any error the transmitter may have (and by factoring in the timebase/aging of the reference oscillator of the measurment equipment, unless, of course, it's synced to GPS or WWV master clock). For complex signals, I'd feel comfortable measuring DQPSK mod accuracy on a constellation chart, but feel it would be a bit overkill for my modular, even if it did have a TZ oscillator.

We use frequency counters to measure the frequency of non-complex signals, RF and AF, usually CW to check the accuracy of the unit, hence the name. We use them to measure....frequency of non-complex, unmodulated signals. The same RF generator that generates simple FM and AM is also used to generate the complex signals, so, again, we need to count the frequency of the carrier in order to determine its accuracy. I'm not sure what you'd prefer to call it, but "frequency counter" is not the mouthful any other definition would certainly impart. I'd reserve that definition for the rare occasion one feels the need or urge to measure "negative" frequencies.

[urbanscallywag]

Sorry I've offended some around here with some trivia.

[blue hell]

[Scott Stites]

Oh, it takes more than that to offend me.

It's just that bit of trivia perplexed me, and I've been in the test equipment field for twenty years. That's the first time I've ever heard anyone say a frequency counter...ain't. And rare is it that I've ever heard HP accused of getting anything wrong from the start (they were like the Moog of test equipment, baby). I don't work for them (or Agilent), BTW. Just a grudging admirer....

Jan, negative frequencies are measured in NegaHertz. Should they ever come into contact with positive frequencies, all matter will cease to exist.

[urbanscallywag]

Complex signals and negative frequencies are some of the most non-intuitive and confusing things I've come across. They are much more useful in communications (Scott goes over a lot of this in his post here) than in synthesizers, so lucky us.

Suppose I have a through zero oscillator (especially useful in JH's FS1A). It has 2 outputs, an in-phase (cosine) and quadrature (sine) output. These "two" oscillators make a complex sinusoid, which really does have a frequency (positive or negative), not just a repetition rate (ducks! ).

The input signal into the FS1A ("made" complex by the dome filter) is fed into a balanced modulator along with the complex sinusoid from the quadrature/through zero oscillator. If the frequency of the quadrature oscillator is negative the input signal is shifted down (down converted) by the magnitude of the frequency. If the frequency is positive it is shifted up (up shifted) by the magnitude of the frequency.

If you've looked at the FS1A you see that you can get up and down shifts at the same time through different outputs. This is because you can change signs on the signal summation to change between down and up converting. But by having a quadrature/through zero oscillator you are able to smoothly sweep between shifting up and shifting down.



So that's one example of how negative frequencies play a role in synthesizers. I don't think there are many. If there are errors above please let me know!

[mono-poly]

And orderd one.

[blue hell]

[factus10]

Well, I'm glad that's all sorted out then. Because all I want to do is tune my synth without relying on hearing beat frequencies