Electronic Circuits and Projects Forum

Have you looked at the new PICs with the CTU peripheral?

http://www.electro-tech-online.com/c.../06/01375a.pdf

Hi,
That's really nice. You CNC-ed the box too?

Great Job and nice finishing.

I've got all the parts except for 16 MHZ oscillator .

Thanks a ton! I bought a DVM with cap measurement but it sucks and doesnt even work... I will make this ASAP

I will get PCBs made of this.. dont worry im not going to sell it. I just want a nice sturdy version. When i order its in sets of 3. Ill be sure to send you 1 thanks

Hi,

Nice product case design. Is that a custom case or found somewhere?

Can it really be as good as 0.01pf?

come to think of it, I suppose the casing is actually a modified toolbox.

Hi 3v0, yeah I've seen the PICs with capacitive touch feature built in. The main benefit of those is they can select between a number of inputs to connect to the PIC comparator. However for this design any old PIC with a comparator will work fine.

Vizier87, thanks! Yep the front panel text is CNC engraved. It's that black/white stuff that is used for permanent front panels. I got the material from a trophy shop.

Atom, sure get PCBs made and I'm not stressed if you sell a couple of PCBs to cover your costs. If you want to sell full kits just give me $2 for each kit you sell..

MrAl, the case was a $6 electronics case from Altronics australia; http://www.altronics.com.au/index.as...=item&id=H0285 I've seen them from other suppliers probably Jameco or Digikey or someone in the USA will have them.

Yes it does INDICATE to 0.01pF. As for accuracy that depends on the calibration and linearity. The calibration I could get to better than 0.2% of a cap value, (I think mine is better than 0.1% but I only had a limited number of 1% caps to test so it depends how good those caps were). The linearity should be quite good, as it has zero function that removes ALL internal capacitance and constant delays (like the comparator switching times) then the only thing that adds to the measured period after that is the external cap.

Please don't think it has 0.01pF overall accuracy! Where the 0.01pF resolution is nice is in seeing temperature drift of caps and seeing the effect of putting your finger near something etc. Or seeing how much a trimcap changes when you put the metal screwdriver in it.

cr0sh, an ATMega + external comparator shold be fine! You need a comparator with fast switching times and good push-pull output. The the ATMega needs to measure the periods as described on the web page and display it. An Arduino may introduce problems as it has long tracks to IO pins and may not make a great oscillator. But then again it might work fine, I don't know.

Thanks everyone for the interest!