I have purchased and bread boardedd a circuit which is made up of 74ls90, BCD counter, 74ls47 seven segment display driver, and some 470 ohm resistors, and 7 segment common cathode displays made by Kingbright. I found this circuit on Aaroncake.net /circuits/counter.asp. I already have over $140 invested in this. I get the numbers to come up but they are random, and sometimes I get random letters. This circuit is to replace a shuffle board game that had 2 PC boards wiped out by 110 volts.
I need some help in getting this thing to work properly, so I can press on with getting the shuffle board back on line.

I hoped this is the way to get this problem out there.

Thanks
Tom

 

The 74LS series of ICs were used in the seventies. 32 years ago!
Like any counter, they count every bounce of the contacts of a switch, pushbutton or relay. The contacts bounce many times per push.

Look in Google for a Debounce circuit.

None of Aaron's circuits have a very important supply bypass capacitor. Most old 74LS ICs need a 0.1uF ceramic disc supply bypass capacitor each.

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Uncle $crooge

 

The first error I see is that you stated the displays are common cathode. The74LS47 is to drive common anode displalys. The circuit shown will come on with a random number showing because the 74LS90 is not reset to 0 on the application of power.
What circuit are you using to trigger the counter? It must be bounce free and TTL compatible.

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The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

Audioguru and k7elp60 have already answered your question. I'm just going to expand on that a bit:

That circuit as posted is just a basic textbook-style outline--it doesn't contain everything you need to actually make it work properly in the real world. If you search this site you will find a lot of other people have had trouble with it for just that reason.

o You need a bypass capacitor on the power pins to get rid of power-supply spikes caused when the counter counts. Otherwise the thing can get false input triggers. Check page 554 in the Art of Electronics for more information.

o You really do need a debounce circuit on the input--even a good switch will make and break contact several times over the first millisecond or so after being switched before it settles down. A debouncer just turns this into one nice transition from On to Off (or vice versa). Read this thread for more information and instructions on how to do it.

o When you turn the counter chip on, its state at the moment after power is applied is undefined unless you give it a reason to reset to 0. Check out this thread for more information. In particular, the second-to-last post in the thread (by Sebi) shows how to wire it a power-on reset circuit to the 74LS90.

Hope at least the links help. I found them (and this board) very helpful when working on my foosball table last year. I keep meaning to clean up my finished schematic and post it with some pictures.


Good luck!

Torben