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Frequency counting without a microcontroller

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rupidust

Sat Sept 22 2007, 09:11PM

Banned
Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

Perhaps you 6 or so people ought to run a search for PIC Wiki or AVR Wiki on google before the year is over.
No one was burn with the knowledge of diodes, resistors, capacitors, and ICs. If you choose to learn them, so to may you choose to know beyond them.

Reaching

Sat Sept 22 2007, 09:32PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

if theres no need for a microcontroller i wouldnt use one. i have logic ics on hand, and not a single microcontroller. i have no possibility to program one and i have no knowledge about the code in a ÂµC etc. so why is it so difficult to understand that some people just dont want to get into ÂµCÂ´s or do not have the knowledge? iÂ´ve build a frequency counter without a ÂµC and it works fine for my needs, and its cheap. i dont want to mass product them so i think im fine..

Ken M.

Sun Sept 23 2007, 01:58AM

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

I look at it as, Do you wanna set up quiet a few parts, or use minimum parts, and learn something new?

Besides uC are very versitile.

But if you wanna use descrete logic over uC, go for it.

ragnar

Sun Sept 23 2007, 04:51AM

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

I didn't intend to open (or argue) the "But you could do this with a microcontroller" can of worms.

The circuit here is a straightforward frequency counter that "anyone" can build with COMMON discrete logic chips, NOT MANY of them, uses COMMON seven-segment displays, and the driver is of reasonable size in comparison to the display.

The simplicity and 'understandability' comes at the expense of some accuracy. **shrug**

Perhaps when I finalize the circuit design, I'll see some it replicated by a few people =)

Firnagzen

Sun Sept 23 2007, 07:12AM

Registered Member #567 Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147

I had a rather peculiar thought when reading this topic-

Whitearc mentions having to reclibrate it everytime you use it. Why can't you use itself to measure the frequency of the relaxation oscillator? Or is that a silly idea.

ragnar

Sun Sept 23 2007, 07:29AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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I don't know why WhiteArc says you have to recalibrate it every time you use it -- I certainly didn't say that; and you certainly don't have to, thanks.

Yes, it can read its own reference frequency -- this is what I actually used as a test signal through development.

For your interest, though, you can't use the reference frequency to calibrate itself; if you lower the reference frequency, you lower the number of pulses per second that would hit the input. But because it counts pulses for a longer period (because you just lowered the refresh frequency), it will read the exact same figure. If you plug the reference frequency into the input, the display reads "002.4" no matter what the reference frequency is. =P

Steve Conner

Sun Sept 23 2007, 10:57AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I agree that this topic should probably be renamed to "Doing things without a microcontroller that are really best done with a microcontroller".

PICs count as "common logic chips" nowadays. And once you've learnt how to use them, they open a hell of a lot more options for you in your hobby projects.

That's beside the point though, if Matt wants to write about frequency counters made out of discrete logic, we're not going to stop him! It's all more quality content for 4hv, and the arguments over whether it should have been done with a uC are quality content too. And the blue displays are so sexy!

PS: About recalibration, there is no excuse for a frequency counter with anything other than quartz accuracy. If the accuracy budget depends on a relaxation oscillator in there somewhere, you need to go back to the drawing board!

ragnar

Mon Sept 24 2007, 02:42PM

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

After the logic rework (which Peter '...' spotted), the revised board layout is a little smaller and even neater. Even just optimizing this was great fun for me.

Here's how it's looking currently.

Who says I etch one to see if I got it right?

ragnar

Wed Jun 18 2008, 05:27PM

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

I still haven't progressed to microcontrollers, but this one had been smirking at me from my junk pile for too long. I've finished this version to such a stage that it may now be comfortably ignored.

There are two PCBs, the display drivers / counters, and the circuit that buffers the input and generates the appropriate timings to reset / inhibit the counters. Both boards are single-sided, with a five-wire interface connecting them together [ground, inhibit (= dispenbl), clock, reset, vcc].

Both the driver chips and the displays are offensively overdriven and get too hot to touch after minutes of operation; I guess this is why god gave us resistor networks, which I am yet to discover.

Volts into the DC jack on one side, wiggles into the SMA jack on the other side, and the displays show pretty numbers. It drifts horribly with temperature, cost me more than my frequency-measuring multimeter, and consumed hours laying out the board. Case closed.

uzzors2k

Wed Jun 18 2008, 05:35PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Cool Matt, your stuff always looks so pro. Btw, where've you been the last two years? I've only seen you here intermittently with just a few new projects.

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