UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 25th Dec 2014, 10:49 pm   #1
high_vacuum_house
Octode
 
high_vacuum_house's Avatar
 
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,910
Smile Trying to make a logic decade divider box

Good evening,
I am trying to make a logic decade divider box for use with a 10MHz rubidium frequency standard. My idea is to have a box with the 10MHz reference sinewave input and then logic outputs each being divided by 10 from 10MHz down to 1Hz.

I have been messing around with various circuits and have come across 2 problems. The first is trying to convert a 10 MHz sinewave to a square wave to go into a divider. I can put a sinewave directly into a logic gate and it does work in a fashion though the output is obviously not exactly very square!! The sinewave is nearly 5V P-P.

The second is trying to get an equal mark space ratio on the decade divider itself. I can divide a square wave by 10 to give a tenth of the frequency out but it keeps coming out as a narrow pulse rather than 50% mark space ratio (i.e a square wave). Is there a logic gate which would do this task relativly easily?
Many thanks,
Christopher Capener
__________________
Interests in the collection and restoration of Tefifon players and 405 line television
high_vacuum_house is online now  
Old 25th Dec 2014, 11:42 pm   #2
cmjones01
Nonode
 
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
Default Re: Trying to make a logic decade divider box

Don't worry about the input to your divider being square. As long as the edges are clean (use a Schmitt trigger to square your sine wave) it will work fine.

To get a square wave output, do your division in two stages: divide first by five, and then by two. The division by five can be using any circuit you like, the output pulse shape doesn't matter. The final divide by two (one flip-flop of a binary counter) will guarantee you a 50% duty cycle, or as near as makes no difference, on the output.

I hope that helps
Chris
__________________
What's going on in the workshop? http://martin-jones.com/
cmjones01 is offline  
Old 25th Dec 2014, 11:45 pm   #3
n_r_muir
Hexode
 
n_r_muir's Avatar
 
Join Date: Jul 2007
Location: Edinburgh, UK.
Posts: 344
Default Re: Trying to make a logic decade divider box

Hi'

Have a look at this thread where oscilloscope time mark generators are discussed.

Oscilloscope Calibrators: Bradley 192 vs. Heathkit IG-4505

https://www.vintage-radio.net/forum/...ad.php?t=54836

Having a 1:1 mark space ratio, while aesthetically pleasing, is not rally necessary. It is usually the leading edge of the pulses that are of interest for timing purposes.

Last edited by Brian R Pateman; 26th Dec 2014 at 9:21 am. Reason: Link to thread added.
n_r_muir is offline  
Old 26th Dec 2014, 11:55 am   #4
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Arrow Re: Trying to make a logic decade divider box

Quote:
Originally Posted by high_vacuum_house View Post
I can divide a square wave by 10 to give a tenth of the frequency out but it keeps coming out as a narrow pulse rather than 50% mark space ratio (i.e a square wave). Is there a logic gate which would do this task relatively easily?
You don't specify what you are using for that ÷10: I suspect you are using a SN7490 TTL chip - or one of its derivatives. If so, there are two ways of achieving a required 'freq. ÷10': the post above by cmjones01 is relevant. Look up the '7490' in the Texas TTL book: IIRC, the connections for what you require are shown there.

Al. / Dec. 26
Skywave is offline  
Old 26th Dec 2014, 4:46 pm   #5
lesmw0sec
Octode
 
Join Date: Jul 2009
Location: Carmel, Llannerchymedd, Anglesey, UK.
Posts: 1,498
Default Re: Trying to make a logic decade divider box

And if you are using TTL - try a 7413 schmitt trigger for sine/square pulse shape, or a 4093 in the CMOS world.

Les.
lesmw0sec is online now  
Old 26th Dec 2014, 4:50 pm   #6
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
Default Re: Trying to make a logic decade divider box

In my days of doing this to provide marker-pips for amateur radio the usual thing was to use any easily-available set of TTL gates [7400] at 10MHz to oscillate the crystal at 10MHz, then put it through a Schmitt Trigger stage [7414] to get the waveform nice and square then a series of 7490 TTL divide-by-N stages.

There was also a 4-legged Motorola chip [MFC4040] intended for electronic organs, that did divide-by-two which was useful when you needed a UK VHF two-way-radio 25KHz or 12.5KHz alignment 'pip'.
G6Tanuki is offline  
Old 26th Dec 2014, 6:45 pm   #7
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,241
Default Re: Trying to make a logic decade divider box

As well as TTL ICs, the CMOS 4017 might do the job (it's a bit marginal at 10MHz, but a 74HC4017 will be more reliable). It's a decade counter by default, but instead it could count to 5, and be followed by one half of a 4013 D-type latch to give a good square wave.

The 4017 has the advantage of decoded outputs, so you need only connect the 6th output to the reset pin to get a divide-by-5 circuit.

Alternatively, rather than use the divide-by-two trick, you could use a 4078 - which is an 8-input OR gate. Feed this with the first 5 outputs of the 4017, and ground the other inputs. You'll need one of these per 4017, so this option might use more packages...

For a Schmitt trigger input (to square up the sine wave), the 40106 is a hex inverter with Schmitt inputs. Alternatively, the 4093 is a quad 2-input NAND gate that also has Schmitt inputs. I'd be tempted to use a dedicated comparator, but that's only because I've got a drawer full of them

Good luck,

Mark
mhennessy is offline  
Old 26th Dec 2014, 7:45 pm   #8
high_vacuum_house
Octode
 
high_vacuum_house's Avatar
 
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,910
Smile Re: Trying to make a logic decade divider box

Many thanks for all of your suggestions

I have after more experimenting managed to get a reliable circuit. I have used a 74HCT14N hex inverting schmitt trigger to convert the sine wave to a 10 MHz square wave.
One of my issues was a poor square wave. This was caused by me not fitting enough decoupling capacitors across the devices

I have then used 4 74HC390 ic's each of which give a divide by 10 and a divide by 100 output so I have cascaded them together to give outputs at 1MHz, 100KHz, 10KHz, 1KHz, 100Hz, 10Hz, and finally 1Hz with a bonus 0.1 Hz output as there was a spare divider left!!

Each of the induvidual outputs shall go through a buffer stage before leaving the unit.

Now I just need quite a few BNC panel sockets !! (10 of them!!)

Many thanks again,
Christopher Capener
__________________
Interests in the collection and restoration of Tefifon players and 405 line television
high_vacuum_house is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 12:52 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.