PIC based high-resolution cap meter

[AtomSoft]

Ok Here is a better view:

 

[Mike - K8LH]

That looks great Jason. I agree with Roman that a ground plane is an important consideration...

 

[AtomSoft]

Yeah i know im still working on it. I have to add a couple caps and the regulator is all. Then ill add the ground plane. I find it a bother in eagle

 

[be80be]

Roman Black Nice job i just got done play with it on a bread board here a vid nice work agin thanks Burt

 

[Mike - K8LH]

That looks great Burt (be80be). What was the nominal value of the cap' you were measuring?

 

[be80be]

I think the bread board is adding about 85pf the cap was a 22 that I use with my crystals there supposed to be 1% caps

 

[AtomSoft]

Great job, ill be ordering the pcbs this week.

 

[Mike - K8LH]

I think the bread board is adding about 85pf the cap was a 22 that I use with my crystals there supposed to be 1% caps

That's exactly why I asked -- I was wondering what kind of stray capacitance there was from the solderless breadboard. I've never been able to use a crystal on the solderless breadboard I have here.

Regards, Mike

 

[be80be]

I never use capacitor on solderless breadboard with crystals they never seem to work

 

[AtomSoft]

Funny, they always work with me Also shouldnt you be able to zero it out ? if so can you connect it via wire and zero out before connecting both ends?

 

[be80be]

Also shouldnt you be able to zero it out

Not on a solderless breadboard any way

I made a pickit2 on one worked fine so I moved it to a strip board and it wouldn't work, I looked and couldn't figure what was wrong. Then it dawned on me I forgot the caps on the crystal didn't need them on the solderless breadboard and had to have them on the strip board.

 

[Mr RB]

The board is looking good Atom! This is fun.

I still have some suggestions (haha);
1. adding another trimpot to let the user do global calibration is a good idea. Please see what i said in post #17.
2. The button on PCB may be under the LCD? I still think the button is better OFF the PCB as they can position it nice on front panel. Then the space on PCB can be used for that 2nd trimpot.
3. Does it really need the ICSP connector? With through hole they/you can program the PIC and plug it in a socket. Removing ICSP connector makes the PCB simpler and smaller and probably makes routing easier.

I just measured two adjacent empty rows on a solderless breadboard (5holes/row) and they measured 3.1pF. Much less than I expected! Maybe it is double that or more depending what is on each side of a row (what is plugged in).

In the past when I have used xtals in breadboards I left out the 22pF caps and it always worked ok.

Burt, did you remove the link for the video? I can't see it on this page but maybe it's my clunky old web browser...
(edit) Can that last statement I had Flash turned off in my browser. I was able to see your vid from the url; https://www.youtube.com/watch?v=9FZDP-8Osyk

If that 107pF is the base reading (ie C1 and all the wires etc) you can zero it out by pressing the zero button (or short PIC pin RB2 to GND).

 

[AtomSoft]

The board is looking good Atom! This is fun.

I still have some suggestions (haha);
1. adding another trimpot to let the user do global calibration is a good idea. Please see what i said in post #17.
2. The button on PCB may be under the LCD? I still think the button is better OFF the PCB as they can position it nice on front panel. Then the space on PCB can be used for that 2nd trimpot.
3. Does it really need the ICSP connector? With through hole they/you can program the PIC and plug it in a socket. Removing ICSP connector makes the PCB simpler and smaller and probably makes routing easier.

I just measured two adjacent empty rows on a solderless breadboard (5holes/row) and they measured 3.1pF. Much less than I expected! Maybe it is double that or more depending what is on each side of a row (what is plugged in).

In the past when I have used xtals in breadboards I left out the 22pF caps and it always worked ok.

Burt, did you remove the link for the video? I can't see it on this page but maybe it's my clunky old web browser...
(edit) Can that last statement I had Flash turned off in my browser. I was able to see your vid from the url; https://www.youtube.com/watch?v=9FZDP-8Osyk

If that 107pF is the base reading (ie C1 and all the wires etc) you can zero it out by pressing the zero button (or short PIC pin RB2 to GND).

1 & 2: Ok will do and remove the button
3. I like the ICSP because will allow debugging.

In the past and till this day i never measured the capacitance on a breadboard but never ever had a problem. Never knew it could jump that much. Try a newer breadboard and see if you have same issue...

I knew you could still zero it out on breadboard.

Roman, ill get working on this today, since i will make the order by friday. Since the max is 50 x 50 mm i can still make the board a bit larger since its already smaller. Its not like its cheaper for smaller than the 50x50.

 

[be80be]

Romam I just posted the video didn't edit it here it is with links showing you design it hope you like this

If that 107pF is the base reading (ie C1 and all the wires etc) you can zero it out by pressing the zero button (or short PIC pin RB2 to GND).

Bread board not much good for a cap meter it doesn't read them right I'll post my finished one this weekend I have a nice box for this.

Thanks gin Roman Black for you hard work nice job

 

[hugo]

Hello Roman,

Nice work ! Thank you for sharing !

How about making an even simpler version of cap meter using a PC terminal as a display and to power it from USB/RS232 port ?
The same thing could be done with a high res frequency meter and or a PIC DDS function generator ...

By the way have you seen this one :

http://www.myplace.nu/avr/minidds/index.htm

 

[Mr RB]

Atom, that was a new breadboard but I only tested 2 rows, capacitance would be more with 3 rows (ie middle row to outer two) and a lot more if they had components with long legs plugged into those rows.

Burt, the cap meter should zero out ok, the zero function in software will remove all the breadboard capacitance and fixed delays like comparator switching times. Then the only thing displayed will be the extra (test) cap when it is added.

Hugo, that is a nice little DDS project in your link! He doesn't say what the top frequency is or the phase accuracy but it's still a cool project.

I'm not keen on PC-driven test gear as it's very limiting when you have to have a big PC next to whatever you are testing. I prefer small self contained testgear so it can be connected to whatever in the field and doesn't have grounding issues or need mains power etc.

 

[AtomSoft]

Hey Roman im working on my own version... so far i can read 1nF to 10uF!!! I need a better resistor to get a better resolution but im using a 1k 1% and get great results. Imagine with a 10k or 100K resistor with a 1% tollerance i would get great results. Im uploading a video now and will post ASAP

 

[be80be]

Now one for inductors would be handy

 

[AtomSoft]

heh i can try but not promising anything

Here is my video:
https://www.youtube.com/watch?v=JXLJFW0c5qA

 

[AtomSoft]

Hey Roman, you think these will do a good job ?
https://www.mouser.com/ProductDetai...=sGAEpiMZZMsPqMdJzcrNwsDBSEuVlBlrnyJmauO2D6Q=