Test Equipment - frequency counter

[Electron Tornado]

I found these two kits on ebay. Has anyone tried either of these?

http://www.ebay.com/itm/DIY-Kits-1Hz-50MHz-Crystal-Oscillator-Tester-Frequency-Counter-Meter-Case-New-/321864867547?hash=item4af0a41edb:g:4pIAAOSwzaJX3Tgw

http://www.ebay.com/itm/Frequency-Counter-Meter-1Hz-50MHz-for-Crystal-Oscillator-Digital-LED-DIY-Kits-/141640365757?hash=item20fa6c76bd:g:SfMAAOSwv0tVMLD4

[Rob Strand]

There's no indication of what the input signal is.  It may be digital and hence require a preamp/front end. It's actually quite a bit of work getting a frequency meter front-end working that produces trustworthy measurements, especially one that gets upto 50MHz.   If you can't trust the measurements it's not much good, might as well be random numbers.

At first I saw 1Hz - 50MHz and assumed it was 1Hz resolution.  However one of the links you gave said:
""five (digit?) Accuracy Resolution ( eg 0.0050 kHz , 4.5765 MHz , 11.059 MHz ) ""
Which implies it has auto-ranging without needing a switch (which is good), and it does down to 0.1Hz resolution.  I don't know how long it takes to produce a measurement 0.1 sec, 1sec,  10sec?

This one looks like it has more professional specs but at 0.1 *MHz* resolution is pretty useless for audio.
It clearly states a 60mV sensitivity, which is good and in the ball-park of frequency meters.
http://www.ebay.com/itm/Blue-0-1-60MHz-20MHz-2-4GHz-RF-Singal-Frequency-Counter-Cymometer-Tester-Meter-/221545339793?tfrom=321864867547&tpos=top&ttype=coupon&talgo=undefined

I cannot give a recommendation on any.   I think you should find out what the first one takes as an input signal, and also ask yourself is 0.1Hz resolution OK for what you need?

Most "real" frequency counters have a period mode which lets you get more resolution for  longer waveform.   Honestly for audio stuff and when designing test gear etc.  I find the period mode far more useful.

[Electron Tornado]

Thanks, Rob. Looking at the one with the case, it looks like the input is coming from some kind of signal generator.

http://www.ebay.com/itm/DIY-Kits-1Hz-50MHz-Crystal-Oscillator-Tester-Frequency-Counter-Meter-Case-New-/321864867547?hash=item4af0a41edb:g:4pIAAOSwzaJX3Tgw



The chip itself may also need to be programmed. There may be enough info here to determine if one of those on ebay is worth a shot, or even if a better version can be done DIY:

http://web.mit.edu/6.115/www/document/16f628.pdf

http://www.microchip.com/wwwproducts/en/PIC16F628A

[alanp]

What's a known-good frequency counter you can buy new for non-silly money? (You know, like how Rigol stuff is affordable, yet still pretty decent.)

[blackieNYC]

Do you need a voltmeter? With a capacitance and frequency meter? This isn't mine (realistic radio shack meter) but it is $60. I'll measure voltage, then frequency on the one meter.
Maybe you need the oscillator. You might find a multimeter that does that. Or a phone app

[Rob Strand]

Looking at the one with the case, it looks like the input is coming from some kind of signal generator.

From what I can guess by looking at the board the front end might be just a single stage transistor stage.   Probably no schmitt-trigger, so it will for nice signals but you might find it has dodgy measurements when you use it in real situations, which can be a pain.  If you find you can't trust the measurements consider building a front end:

1) Pic with transistor amplifier front-end:
http://1.bp.blogspot.com/-irbvujT5QyU/TmIj-fYzSMI/AAAAAAAAALs/knq6o9OS_Gw/s1600/Frequency+meter.png

The things you need for the front-end are:
- JFET buffer with protection
- Schmitt trigger  maybe 50mV 100mV hysteresis

2) This one looks like it does the trick but the front-end buffer might be a bit overboard, also an electrolytic C1 is not good use a 100nF .  C5 through to U2 is the schmitt trigger.  The hysteresis is probably a bit high, which is why the first stage has some gain.  Also might need to tweak R7.  The good thing it gets you to 50MHz, or at least close to it.
http://www.qsl.net/yo5ofh/pic/frequency_meter_with_pic_16.htm
http://www.qsl.net/yo5ofh/pic/frequency_meter/weedfreq.gif

3) This is a typical 50MHz front-end.   This buffer looks good and is simpler/better.
http://electronics-diy.com/schematics/671/30706_13mg.jpg

4) This one (from signal input through to A1 and including the 10k) has the simpler buffer and uses an easy to get comparator but will only get to to a few hundred kHz.   T
http://www.next.gr/uploads/57/sound-frequency-meter-diagram.gif

[Rob Strand]

Do you need a voltmeter? With a capacitance and frequency meter? This isn't mine (realistic radio shack meter) but it is $60. I'll measure voltage, then frequency on the one meter.

Most frequency meters on DMMs are a bit dodgy.    Some have digital innards which work well - the tell tail sign is the specs are quite accurate and will have a top-end range beyond 200KHz.   The majority use a 555 timer and an analog method.   They often have a fairly large "+digit" accuracy spec  so they generally can't be trusted to within a few hertz.   They are only good for rough measurements and generally need a fairly nice signal to trigger reliably.

Like most things it all depends what you need it for.   If you want to check drift of an oscillator you need a something that is digital and has a good front end.   For this the DMMs are no good. The values bobble around more than the thing you are measuring.