Lets talk about Frequency counters

Thread Starter

Wendy

Joined Mar 24, 2008
22,155
This is a continuation of my lets talk about series, the first being Lets talk about quartz.This thread wil discuss how to make a really simple frequency counter. As usual I am bored out of myskull. I literally have nothing better to do. I will g step by step an show how I would mak a freq counter including schemaics. Maybe when I am on my feet I will build it. It would be a usefull addition to many projects such as a DIY function generator.

The Basics

First a simple block diagram...

Counter.png

While the time base is not shown it is assumed and is a vital part of the instrument. I have a very simple design in mind that I have built and tested.

Tobe continued...

 

RichardO

Joined May 4, 2013
2,271
I am still using a counter built from the Intersil evaluation kit for the ICM7226. :)

The biggest problem is accurately calibrating a frequency counter... without another frequency counter.
 

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Thread Starter

Wendy

Joined Mar 24, 2008
22,155
The system I'm thinking about may surprise you. Actually you need precision frequency source. Like another crystal oscillator.The Meterology shop I worked in used 10Mhz from an atomic clock.
 
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Externet

Joined Nov 29, 2005
1,528
Please educate me...
An atomic clock that has its time transmitted on 10 MHz radioed signal... If the 10 MHz is taken as reference to calibrate a frequency counter; the atomic clock is contributing with nothing for accuracy. The broadcast RF would be the one being used as reference.
The crystal/oscillator of its RF signal would have to be derived from the atomic clock to be very precise, and that is if there is a sharp tuning indicator at the receiving end.

Or are we referring to a real atomic clock on the bench ?

¿?
 

SLK001

Joined Nov 29, 2011
1,548
Also, the old colorburst crystal (3.579545 MHz) was used as a precision reference for calibrating counters, as they were accurate to the Hertz.
 

nsaspook

Joined Aug 27, 2009
7,470
I built something like that way back when I was just getting started with digital electronics and TTL. Found it in the bottom of the junk box. A little busted up but I bet I could make it work again without too much trouble. Those were neat display proto boards, 871-0719 universal display card

Four digit frequency counter, I think.

Four digit display board

Precision time base board and signal processor. 250.000 KC xtal timebase using mps6520 and rs-2031 transistors:D
 

Thread Starter

Wendy

Joined Mar 24, 2008
22,155
This was a qty2 full cesniun atomic clocks similar to those used by WWV (two large consoles). orNIST https://www.time.gov/. They received th 10Mhz signal and did a phase comparison with the 10Mhz signal out of Colorado. you could the ionosphere move causing a phase shift to be recorded on the chart recorder. When we adjusted the crystal oven in the higher dollar equipment we would display the10Mhz standard and measure drift in nanosecond s over a fixed time. this tested both check accuracy and stability.I is odd I never mentioned WWV (the call sign for the
NIST but it is assumed I did, I wouldn't be surprised if the atomic clock output is not used for the10Mhz base freq. It would make sense.AWe used the 10mhz standard factory wide Most godd equipment has an external time base input.


Location:
Dallas, TX (GMT-5 w/ DST)
Any equipment without a crystaloven is not very precisionAstand alone crystal oscllator is good but tenperatue causes drift so you put the crystal into a temperature controlled environment. I was thinking of a watch crystal actually for this counter.
 
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k7elp60

Joined Nov 4, 2008
562
This is a continuation of my lets talk about series, the first being Lets talk about quartz.This thread wil discuss how to make a really simple frequency counter. As usual I am bored out of myskull. I literally have nothing better to do. I will g step by step an show how I would mak a freq counter including schemaics. Maybe when I am on my feet I will build it. It would be a usefull addition to many projects such as a DIY function generator.

The Basics

First a simple block diagram...

View attachment 128963
Wendy I think on your small diagram where you indicate 1 Hz input, should be 0.5 Hz, so the counter will be enabled for 1Hz, as the square wave would be logic level high for 1 second and low for one second.

While the time base is not shown it is assumed and is a vital part of the instrument. I have a very simple design in mind that I have built and tested.

Tobe continued...
 

MrChips

Joined Oct 2, 2009
21,664
You could use a temperature controlled 32768Hz crystal as a reference.
Use this to drive a time-of-day clock circuit. Check the time against a calibrated time such as WWV every 12 days.
If you can trim the crystal so that you are accurate to 1 second after 12 days, that is an accuracy of 1 ppm.
 

AnalogKid

Joined Aug 1, 2013
8,536
Also, the old colorburst crystal (3.579545 MHz) was used as a precision reference for calibrating counters, as they were accurate to the Hertz.
FCC rule in the 70's was +/-10 Hz.
And there is a chip that counts it down to 60 HZ.
If you're talking about the old National Semiconductor part, its output was not a perfect 1.00... Hz because the subcarrier frequency is not an integer.

ak
 

Thread Starter

Wendy

Joined Mar 24, 2008
22,155
A Time Base

I used this time based on my digital clock thread https://forum.allaboutcircuits.com/threads/digital-clocks.52161/ .I didn't finish it but iy held better than a minute/week though your results may differ Thhis is not a high priced counter, It will have no frequency ranges(which are controlled at the time base level. In short, it is good enough.Twas surprised it worked so well on a protoboard, but it did.

1Hz TB.png
 
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AnalogKid

Joined Aug 1, 2013
8,536


The MC14553 is (was?) all of the digital guts of a 3-digit frequency counter, everything in the box above. Cascade two parts for 6 digits.

ak
 

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Reloadron

Joined Jan 15, 2015
5,609


The MC14553 is (was?) all of the digital guts of a 3-digit frequency counter, everything in the box above. Cascade two parts for 6 digits.

ak
Forrest Mimms used that counter cascaded for a six digit counter in his now ancient Engineers Notebook you will see it in the link on pages 32 & 33.
The heart of any good counter is the uncertainty of the time base. I worked with early HP systems like the 524 and later 5245L which boasted a 50 MHz mainframe. The better models used a quartz crystal in an oven. One calibration standard I recall was an Arbiter which was a television receiver (US use only) which derived and divided the color burst frequency. You needed network TV and not local affiliates unless they were on network at the time. Spectracom also had a line of VLF tracking receivers for use with WWV. Most receiver systems I see today are GPS. Looking back at time and frequency dissemination over the last 40 plus years yields some cool stuff.

Anyway, here's the 6 digit counter using the old 14553.

Ron
 
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