Digital Rev-counter

[OwenParticipant @owen]

[OwenParticipant @owen]

In the MEW issue147 there is a build article for a digital rev-counter. Has anyone else built this item and if so what results did you get. I’ve been working on this off and on for some time and am having some problems. The counter lights up but does not display a count,remains at zero. the scope shows pulses at the output of the circuit that vary with RPM but cannot get the dispay to show them. Any ideas appreciated.

Owen

[Ian S CParticipant @iansc]

There is one in ME , it might have been back in the 90s, I just use my frequency meter, Tricky Dick kit set (Aussys & Kiwis will know who). Ian S C

[OwenParticipant @owen]

I was hoping to find someone who has built the one in issue 147 of the MEW as I’ve already buit it and I’m probably just missing some detail in getting it to run. Dick Smith doesn’t sell any kits, anymore at least not in the store I was in last month when I was on my annual trek to Oz. Anyway thanks for the reply.

Owen

[John OlsenParticipant @johnolsen79199]

I don’t have the circuit so can only comment generally on digital fault finding. You can use a multimeter as a logic probe, or you can use an LED with a resistor as a simple, not very sophisticated probe. Or else a logic probe tends to be not too expensive to buy, at least last time I wanted one they were not dear. Some multimeters will havea logic probe feature provided. A bought one will do things like show that it saw a very short logic pulse that would not show on a meter or simple LED.  If the design is built up from standard items like counters, decoders and logic you can trace what is happening through the circuit. There should be changes of state happening in the counters while it is counting, and at the end of the counting time the final count shget transferred to some latches. of course with modern designs, this could all be done in one chip, making it much harder to diagnose and fix.

 

regards

John

[Ian S CParticipant @iansc]

Theres quite a bit about a digi tacho on Tony Jeffree’s model engineering pages (along with a lot of other bits and pieces),

http://www.jeffree.co.uk/modelengineering.html

                                                                                            Ian S C

[Douglas JohnstonParticipant @douglasjohnston98463]

Hello Owen – I built this tachometer a while ago and it works very well on my lathe. It is possible you may have bought the wrong display unit as I fell foul of this myself. The display units come with different input sensitivities ( 50-300V or 0-5V). I bought the  50- 300V unit and could not get the display to count, just as you found, all digits reading zero.

               If this is your problem, both units are essentially the same except for R16 on the printed circuit board which needs to be changed from 47k to2k. It is quite easy to do this with a fine soldering iron. I have a letter in ‘scribe a line’ in issue 153 relating to this problem. I hope this is of some help.

Doug

[OwenParticipant @owen]

thanks all for your replies,since Douglas has built the thing and it works I can only assume I’ve made a boo in the build. I do have the right meter 0-5v so I’ll go back over what I’ve done and see what I can find.I`ll let you all know what  happens,may take a while as it`s a bit busy here just now.

owen

[Billy MillsParticipant @billymills]

Owen

Check that your pulse input is on p6 not p1 and that pin 1 is not connected ( holding reset would cause the 0000 state to be held). Check that the 470nF IS 470nF not 470pF. Fast test would be to short the 470nF with the spindle turning and check the count.

 

 Regards

Alan.

[ianjParticipant @ians]

Hi Owen.

I’v just built this rev counter.I had a problem which turned out I had the collector & emitter of the optotransister reversed, when I corrected this all worked o/k.I contacted Mike Crossfield who sent me this explaination of how the circuit works:-

 

“With everything correctly connected, and the opto slot clear, the optotransistor will be switched on by the illumination from the LED, and its collector (pin 3 on the opto switch) will be near to 0V. This will turn TR1 hard on, and its base will be at around 4.3V.  The collector of TR1 will be just below 5V.

 When the slot in the opto switch is blocked, the optotransistor will be turned off.  The collector of the optotransistor will be pulled up to 5V by the 2k2 resistor.  TR1 will be switched off, and its base will also be at 5V.  The collector of TR1 will be pulled down to 0V by the 3k3 resistor.

     Tr1 collector is connected to the input of the digital frequency meter (pin 6) via a 470nF capacitor. Pin 6 is also connected to 0V by a 2k2 resistor. As explained in the article, this arrangement makes sure that the display returns to 0000 when the machine spindle stops. However, because dc voltages are blocked by the capacitor, it also means that you will not get meaningful measurements with a voltmeter at pin 6 during static testing.”

 

 

With a scope on the o/p pin I get a nice 2.5v amplitude square wave.If you have the same LED display I have the connections are different to those in Mikes article. Looking at the LED display with the pins at the bottom, from left to right::-

 

   pin 1 & 2 no connection, pin 3 +5v. pin 4 -5v (0v) from power supply, pin 5 no connection & pin 6 i/p. Hope this helps.

 

    Ian

[VersabossParticipant @versaboss]

For those who are not so much in electronics, I think I can recommend this gadget:  

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370431851998

At least the price is right! My item is under way somewhere…

(and after half a dozen unfruitful attempts I gave up trying to ‘correctly’ insert a link. Seems my brain is too old to get the finesses of all those (a good dozen)  input fields under the chain symbol, which all do nothing…..)

Greetings, Hansrudolf

[Sub MandrelParticipant @submandrel]

Hi Hans,

 

Copy link

 

highlight some text.

 

Click the link icon

 

paste the link in the URL field

 

Click OK

 

 

If that doesn’t work, change top Firefox, ‘cos it works in Firefox here!

 

Neil

[VersabossParticipant @versaboss]

Thanks Stub, that’s one of the methods I tried, but didn’t work. I use Opera; Firefox also because some sites don’t work correctly in the former (e.g. electronic banking). But I prefer much the ‘look and feel’ of Opera. Although not the latest version, which is a nuisance. It is possible to ‘improve’ a product to death, unfortunately….

Greetings,

Hansrudolf

[OwenParticipant @owen]

again thanks everyone for the replies. Ian I think your post will be a great help. I still haven’t got back to this project due to other priorities. It’s the Christmas season and we (our club) is doing some night running for the public. Cold but fun.

Owen

[TerrydParticipant @terryd72465]

Hi Hansrudolf,

 

A brain is never too old to learn.   I have tried Neil’s method to add a link in Opera and it does work ok. Another method is as follows:

 

open the ‘link’ window with the icon and paste or type the address into the ‘Url’ field;

then use the ‘Target’ drop down menu and select ‘New Window’ (this opens a new page and keeps Model-Engineer open at the same time);

 

Then type a suitable text into the ‘Title’ field such as “eBay electronic gizmo” and it will put this text into your post and attach the url (address) to it.

 

I tried it with your link and it looks like this:

 

eBay electronic gizmo

 

Regards

 

Terry

Edited By Terryd on 08/12/2010 13:45:04

[TerrydParticipant @terryd72465]

Hi Hansrudolf,

 

P.S. it also prevents the ‘table stretch’ problem with long addresses.

 

Terry

[_Paul_Participant @_paul_]

The eBay electronic gizmo is very versatile and reliable I use mine on my ML7, my Taylor Mill and even my Boxford & Acorn shapers, cost under a tenner including shipping from China.

 

 

Paul

[Author]

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