Economy Frequency Counter & Crystal Tester

RE: Economy Frequency Counter & Crystal Tester

jw0752 — Sun, 24 Apr 2016 04:52:29 GMT

I have continued this Blog as a Part II at this link:

https://www.element14.com/community/people/jw0752/blog/2016/04/23/frequency-counter-and-crystal-tester-part-ii

John

RE: Economy Frequency Counter & Crystal Tester

D_Hersey — Sun, 10 Apr 2016 16:31:17 GMT

A counter front-end is like an FM detector -- we want all of the gain we can get because we only care about edges.

You may have some fun if you google 'ecl prescaler'

RE: Economy Frequency Counter & Crystal Tester

jw0752 — Sun, 10 Apr 2016 15:32:38 GMT

Hi all,

Last night I was doing some testing of the limits to the input signal level and I found one of the actual limits and latched up the input to the PIC16F628. Now when I put in a crystal or inject a signal all I get on the display is nonsense. After a review of the Data Sheet (180 Pages) of the 16F628 I found on page 135 that the RA4 (Pin3) input can not tolerate more than -0.3 volts below Vss. I have been feeding full sine and square wave 7 volts PP to the input. I got what I deserved but it re-enforces the need for some sort of buffering on the raw input to this frequency counter. I will continue to look for a proper front end while I wait for my next China Mail Packet. The original designer has a recommended preamp circuit on his web page and this is probably a good direction to try. It would be nice to have some sort of gain control so that a range of input voltages could be used.

John

RE: Economy Frequency Counter & Crystal Tester

D_Hersey — Sun, 10 Apr 2016 14:37:17 GMT

ARRL publications from a few decades back are loaded with schematics for counter front-ends.

John, if you need a box for a project, remember that I am the proud owner of a really nice laser cutter. I stock most colors in nom. 3mm and 6mm acrylic and some in-between. My cutter is reputed to properly interpret circles, though I haven't tried this feature. In practice my kerf is about 1/3 mm, if you are trying crenellation joins. I need *.dxf files. You can generate these with Corel Draw or Inkscape.

This is pretty fun, accurate cuts in acrylic without tooling!

RE: Economy Frequency Counter & Crystal Tester

phoenixcomm — Sat, 09 Apr 2016 22:08:13 GMT

Brillant!![View:/resized-image/__size/337x252/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-427dfc50-1e87-4a3c-bd7c-756d49cc1947/5355.contentimage_5F00_181146.jpg:337:252]
I Want One!!

My Freq/Counter/Timer (Racal Dana 9000) was lost when I lost my house oh, well. The only Freq/Counter/Timer is part of my Tektronix 475A Scope. Now do get me wrong. Now this Scope was around in the late 70's. You do the math. The beast works great but for how long. And it would be way cool just to have a small counter around, and yes, I too have the errant crystal.

Cris H.

RE: Economy Frequency Counter & Crystal Tester

mcb1 — Sat, 09 Apr 2016 11:27:46 GMT

Any ideas on how to cut holes in this type of material would be appreciated.

I ran across these years ago and they are brilliant for holes in many materials.

They go by various names but Step drill seems to be one common name

Steel Step Drill Set - 3 Piece, Titanium Nitride Step Drill Bits

Cheers

Mark

RE: Economy Frequency Counter & Crystal Tester

DAB — Fri, 08 Apr 2016 19:49:37 GMT

Great post @John

I am impressed with the project and kit.

I think you got your 7.95 worth on this one.

DAB

RE: Economy Frequency Counter & Crystal Tester

shabaz — Fri, 08 Apr 2016 16:52:34 GMT

Hi John,

Nice project!

Just thinking, if you like, the input could be like the diagram in this PDF, figure 6a, with a 5V-powered 74AHCT14 logic gate (guessing the PIC is running at 5V?), with a couple of high-value resistors to set the input to about 1V (e.g. 82k and 330k forming potential divider if you're running from a 5V supply), and then feed the input using a capacitor, e.g. 100nF. Also a couple of diodes to prevent overvoltage, e.g. 1N914, placed in parallel with the resistors, cathodes pointing up. This would need about 2V p-p so could be better.

I remember doing something similar to try and get engine RPM years ago! Can't remember if I ever got it working : )

RE: Economy Frequency Counter & Crystal Tester

D_Hersey — Fri, 08 Apr 2016 16:39:20 GMT

Sometimes, you can get little metal tube from the hobby store and use a file to turn the end into a little knife blade and put it into drill press set up to turn slowly. This slices the hole in the poly, keeping things clean. It seems step drills work fairly well in this material, better than twist drills, anyway.

RE: Economy Frequency Counter & Crystal Tester

D_Hersey — Fri, 08 Apr 2016 16:02:55 GMT

Holesaw meebe. Twirling a penknife?