Originally Posted by blueroomelectronics

I was thinking on doing a PCB for the might be popular LC meter. There is a better 16F628A version. I'd like a frequency & duty counter too if I did it. Might base it on a 16F88 instead. Would also like to see if it's possible to get the internal comparator working in the design.

I got the internal comparator working as an oscillator on a '628A Bill. It ties up the TMR0 T0CKI pin (RA4) though so I had to setup TMR1 as the frequency counter and I fed the comparator output to the T1CKI pin (RB6). Here's how I setup the comparator;

Code:

MAIN    movlw   b'00000110'     ;                                 |B0
                                ; b7 = C2OUT                      |B0
                                ; b5 = C2INV                      |B0
        movwf   CMCON           ; turn comparator on              |B0
        bsf     STATUS,RP0      ; bank 1                          |B1
        movlw   b'00001111'     ; RA4=output, RA0-RA3=inputs      |B1
        movwf   TRISA           ;                                 |B1
        movlw   b'01000000'     ; RB6 = input (T1CKI)             |B1
        movwf   TRISB           ;                                 |B1
        bcf     STATUS,RP0      ; bank 0                          |B0

Just need to fabricate a new prototype and finish the software. I was using the serial port and Hyperterminal instead of an LCD.

Originally Posted by dipmicro

Actually, there is no .22uF capacitor in the kit at all, I do not even carry such value.

The .22uF cap is the same color as the 47uF. I'm sure it just slipped through from your supplier.
I'm getting another crystal tomorrow and I'll let you know if that solves the problem.

I replaced the crystal and the board works great. I wrote a quick program and everything seems to be working.

Thanks for all your help everyone.

Jim

Originally Posted by dipmicro

Jim, when did you order your Inchworm? Is there anything I can do to make up for the frustration with the crystal?

I ordered on April 27.
I think shipping to the states costs more than the crystal, so maybe if you could end world hunger...
I'm just happy that everything works now. It's a great little kit.
Thank you
Jim

Originally Posted by dipmicro

The previous message came out as a babble because I was typing it while interrupted several times. I actually would like only to get some feedback on this:

I would think that only direct measurement with a very high impedence, low capacitance probe on the OSC input pin, measuring amplitude and frequency would be the best test. I guess that once one validated a given manufacture's crystal that you shouldn't have to test each one unless you change vendor or crystal part number.

It's hard to guess if the problem is just poor quality control with that one batch of crystals or if their unpublished specifications were not compatable with the PIC oscillator circuit. Only further testing could determine more.

Lefty

Originally Posted by dipmicro

After researching this problem little bit, I am starting thinking that the 33pF may load certain types of crystals too much.

Still need a workaround for people who may have or will run into this problem with Inchworm units already shipped so I can post it on the website.

I do not currently have "bad" crystals, but can someone who had this problem try to run Inchworm with original non-working crystal and try to remove the 33pF capacitors entirely or replace them with 15pF?

The first person reporting successfully tested workaround (of previously dysfunctional unit due to crystal) that can be aplied even by the beginner will get free Inchworm from me for his efforts.

Will the free Inchworm come with a good crystal? Just kidding, nice to see you try and get to the root of this problem and sharing your findings. I'm sure we can all learn from the experiance and sharing experiances is what it's all about........

Lefty

Originally Posted by dipmicro

After researching this problem little bit, I am starting thinking that the 33pF may load certain types of crystals too much.

Still need a workaround for people who may have or will run into this problem with Inchworm units already shipped so I can post it on the website.

I do not currently have "bad" crystals, but can someone who had this problem try to run Inchworm with original non-working crystal and try to remove the 33pF capacitors entirely or replace them with 15pF?

The first person reporting successfully tested workaround (of previously dysfunctional unit due to crystal) that can be aplied even by the beginner will get free Inchworm from me for his efforts.

I have 15pF caps here and a working Inchworm. If someone will send me a 'bad' crystal, I'll give you an answer for free.

I changed the 33pf to 15pf and the original crystal works perfectly. That work around did the trick.

Thanks again to everyone for all your help.

Jim