Roman you are definitely right it would be easier, but not so much fun, and I would probably learn less! I won't discount going that route, but I might have a go at it anyway. I had a quick search for frequency counter kits, and came across an old post of yours at electro-tech online, did you ever build that?
...

No, I canned that idea. The problem with measuring "frequency" over 1 second is that the resolution is terrible for low frequencies. So there was little point of having the xtal oven giving perfect timing if the freq being measured was 200Hz with +/- 1Hz error!

In the end I calibrated my old bench freq meter to a GPS time pulse and got that down to <1PPM error.

A well designed PIC/AVR based frequency meter will measure low frequencies as periods, which makes them a lot more complex to write code for but means that the accuracy and resolution of low frequencies is still good. I have built PIC frequency meters using that system too but have never released the project as there are already lots of good PIC/AVR based frequency meter kits around.

Also for signal generation now I am more often using digitally generated frequencies which make a very accurate and stable frequency. That means I am not reaching for a frequency meter very often these days.

 

Hey How you making out over there ????

 

What me? Making out at ETO forum?

I make out fine, there's lots of good electronics people there and no "psych101 trolls".

 

I've been running around in circles to a certain extent... When I first read the data-sheet, I thought I had to produce a sawtooth of around 4Vpp, of course that was given a +/-12V supply, which I have on my breadboard. However when I read a bit further into it I realised that:-

• A) I have a +/-12V supply on my circuit
• B) the sweep voltage should be 1/3 total supply voltage -2V so 24/3-2=6 (sweep voltage)
• C) the voltage should be swept down from +12V so peak voltage of sawtooth=12V, minimum voltage of sawtooth is 15-6=9V
• D) from the above the sawtooth needs to be positioned at +9V
• E) the sawtooth needs to be inverted
• F) I needed to add a diode to both Vcc (pin6) and duty cycle adjust (pins4&5) to reduce total supply seen by 8038, such that pin8 could go to a higher voltage and facilitate the sweep function.

Anyway it was getting a bit too intense so I've left it alone for a few days, to try to get a fresh perspective.

On the up side I built Roman Black's capacitance meter, I had the parts and needed one to check capacitance for the timing capacitors. It works really well and was easy to build. I've ordered a sexy aluminium box for it and when all is in hand, I'll make another post to show and tell.

 

Hi Bance, congrats on the cap meter! I'd love to see photos.

Back on topic and re your sweep generator, maybe you could add point G); if you use a constant current circuit to to charge the ramp cap you will get a nice linear sawtooth waveshape.

 

I've been running around in circles to a certain extent... When I first read the data-sheet, I thought I had to produce a sawtooth of around 4Vpp, of course that was given a +/-12V supply, which I have on my breadboard. However when I read a bit further into it I realised that:-

• A) I have a +/-12V supply on my circuit
• B) the sweep voltage should be 1/3 total supply voltage -2V so 24/3-2=6 (sweep voltage)
• C) the voltage should be swept down from +12V so peak voltage of sawtooth=12V, minimum voltage of sawtooth is 15-6=9V
• D) from the above the sawtooth needs to be positioned at +9V
• E) the sawtooth needs to be inverted
• F) I needed to add a diode to both Vcc (pin6) and duty cycle adjust (pins4&5) to reduce total supply seen by 8038, such that pin8 could go to a higher voltage and facilitate the sweep function.

Anyway it was getting a bit too intense so I've left it alone for a few days, to try to get a fresh perspective.

On the up side I built Roman Black's capacitance meter, I had the parts and needed one to check capacitance for the timing capacitors. It works really well and was easy to build. I've ordered a sexy aluminium box for it and when all is in hand, I'll make another post to show and tell.

Any updates boss???

JAy