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Frequency counting without a microcontroller

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Ken M.

Mon Apr 23 2007, 08:12PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

As a matter of fact you can even get samples of Micro controls namely PIC's I have a few, my personal choice for a high res digital display would be the mamoth PIC16f777-17p Its a 40 pin but it can handle driving 8 digits at a very high accuracy, and thats with 7segment displays. As for programming software, you can demo Pic basic and pro at compilerspot.com i think...its been a while and besides I have Picbasic here at home and its great being able to type in basic phrases to run a system. As well as Steve and the others...your board looks awsome

, you make it, or did you get a PCB manufacture to make it?

Steve Ward

Mon Apr 23 2007, 08:50PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Well, my school is very heavy on digital design (even though its not my area of focus). Now that i know how to program uCs and FPGAs (field programmable gate arrays), i dont think i could ever do electronics without them. Up until about 4 months ago, i think i was right along with you BP... thought i could just manage all the stuff i wanted to do with gates.

Anyway, you are certainly capable of learning these devices, so maybe in a few months you can start the "Frequency counting WITH a microcontroller" thread, where you can discuss the advantages and disadvantages you find with each design

.

Funny Conner mentions synchronous design... In my digital electronics lab i once got "made an example of" by my TA for BAD design practice for gating a clock signal to one of my flip flops (despite this, the circuit actually did work exactly as required, as i expected). If he saw this frequency counter, i think he'd blow a gasket :P. Personally, while i think true synchronous design (where you dont mess with the clock!) is always better, i dont frown upon little RC tricks and stuff as long as its for your own uses.

ragnar

Wed Sept 19 2007, 07:47AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Well, you might think of this as letdown of the year. Steve reckoned in April that in a couple of months I could have got into microcontrollers. Shamefully, I didn't. I'm still doing it with 40-series logic.

I made this frequency counter once before, and then after assembling it, discovered that the segments on the LED displays I used didn't line up with the datasheet. Wrong datasheet. My fault. I got thoroughly frustrated and tossed the board into my junk projects tray for a rainy day.

Now, in September I needed a frequency counter. Sure, I've got one in my oscilloscope, and I've got one in my multimeter, but for some reason, I wanted to build a signal generator with one in there too. But what actually reminded me was when I saw the newly available BLUE seven-segment LED displays at my store. They're so pretty.

So, I redesigned the circuit, and, without the help of an autorouter, was able to get the four CD4026s connected to the displays, their clocks/carries together, their disp.enbl.in/disp.enbl.outs together, their resets together and their inhibits together, on one layer without a single jumper.

Oh, and because I only have a hand-drill here, everything is surface-mounted. I surface-mounted the chips directly, because if I used sockets I wouldn't be able to get the solering iron tip down between them to solder their legs to the board.

Now I use a CD4060 (with oscillator) to get my "reference" clock. I divide it down, Q10 & Q9 & Q8 & Q7 & !Q6 to give me a the "inhibit" period. I use "inhibit" & !Q5 & !Q4 to give me my "reset" pulse. Now the relationship between reset and inhibit is non-arbitrary, and everything is a lot more predictable and a lot more stable.

The one-off calibration involves tuning the CD4060 oscillator until the numbers displayed match the frequency of your test signal. The display refresh rate will change, but who cares?

The two improvements I made whilst calibrating it were realising that a ~15Hz refresh rate made the "counting pulses" stage almost unnoticable. It might only be 1/100th of a second, but the '0000' segments were juuust momentarily visible. By hooking the "display enable" pin to "inhibit", the display is only turned on when the numbers aren't changing -- with a suitable refresh rate, my eyes' POV makes the display look like it's on all the time. Beautiful.

Now I prescale it as much as I want, and it doesn't matter if it's I use a binary or decimal chip because I can just factor it out by recalibrating. Squee!

Who wants one?

...

Wed Sept 19 2007, 02:25PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

sweet!

It always amazes me that you can cram circuits so closely on a 1layer board (although it looks like you needed a little rework over on the clock generator side...).

As soon as I get a signal generator I will start looking into a decent frequency counter

Marko

Wed Sept 19 2007, 06:43PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Matt those blue displays are beautiful.
Apart from maybe being a bit inaccurate the circuit is cool.
Have you considered to use une of those 32khz watch crystals for reference?
It would add a lot of IC's, though.

My fault. I got thoroughly frustrated and tossed the board into my junk projects tray for a rainy day.

That's why I use donutboards.. and still I find more than enough things to get frustrated with

Hazmatt_(The Underdog)

Wed Sept 19 2007, 07:19PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I never could get the right frequency divided down because my local store never had the right crystal for a 100Hz reference, so I got some from Mouser. The other frequency counter thread has it, which is like 3.27MHz or something... that's the one you would want to use for your standard.

Glad to see it working! I was wondering how you would solve the missing latch problem.

ragnar

Thu Sept 20 2007, 02:01AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

No offense intended, but I did want to compete a bit with your "World's simplest frequency counter" thread.

I mumbled under my breath that it couldn't possibly be simple -- it has TWENTY chips!

I just wanted to brag that I could do it cheaper and dodgier with six chips.

Hazmatt_(The Underdog)

Thu Sept 20 2007, 03:26AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

But Matt, I can do it in 4 and it won't be dodgy, it all depends on what chips you select and how you implement it.

The reason I did the 'sledge hammer to squish a fly' version is for everyone to see how the technology works, and for a few other reasons too:
1. sequential logic
2. latching and how memory works
3. no timing capacitors, its all gated so the only deviation is from the crystal, which by the way could be scaled to 100MHz and in an oven for perhaps 1ppb tolerances.

As far as rock solid design goes, I think that's pretty much there.

I liked the 4026's because conceptually they would do the same job in fewer IC's, so yea I liked them too. But when I found the combination of the 4011 and 4553, I could do a 3 1/2 digit frequency counter that would be rock solid with those from the 4000 family, then use the 4060 with the right crystal, fed to the 4017 as my timing engine, and bam... rock solid in 4 chips. So if you want to beat me, you can try but I think that pretty much sums it up.

Conversely I could use the 4060 and 4017 to generate my timing and send that to the 74C925 and do it in 3 chips if you want to be beat out by 2:1, so its your choice. heh.

I was really interested in the strobe situation though.

...

Thu Sept 20 2007, 03:54AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Using a multiplexed display driver is no fair

I guess we need to change the competition to 'chips not including the display drivers'

Also hazmat, I doubt you would be able to get 9 digits out of your design (enough to be able to see the 1ppb stability you quote), due to pratical limitations in the max frequinecy you can use If you run the clock at 1hz (much slower than that and counter wouldn't be very usefull...), and your input frequinecy tops out at 40MHz (although the chips are only reated for 15MHz even at 15v), you stiil only get 7.5 usable digits... Unless you found a way to get subHz resolution with resonable refresh rates that I overlooked.

Hazmatt_(The Underdog)

Thu Sept 20 2007, 08:49PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

1ppb clock stability is what I was talking about.

Multiplexed driver chips are fair because he's using a divider decoder. If divider decoders aren't fair then what I did is the only 'fair' way to build the counter, 1 chip per function.

Anyway, that doesn't matter, I'm glad to see interest in frequency counting because it requires some thought and I havne't seen much discrete stuff out there that actually works.

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