# Need Help How to Make Schematic on a Basic Project - Electronic Scoreboard (bsktbll)

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Disconnect the wires leading from the counter to the 7 segment decoder.

Ground all the inputs to the 7 segment decoder. Does it display 0?

Take each input to logic high one at a time (just leaving them floating -- i.e. connected to nothing -- should work for testing). The decoder should give you the values 1, 2, 4, and 8.

then measure the voltage on the output of the counter. Are they all at 0V after you hit reset? Which pins are you testing (i.e. which pins do you believe are the outputs).

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#### barbaro

Jul 11, 2011
21
Hi Steve,

I disconnected all the wire leading to the 7 segment - which is pin 2,3,6 and 7. I ground all inputs to the 7 segment and it doesnt display zero '0', it displays 8 but if i disconnect the GND on pin 2 on the decoder, it displays zero. I take input to logic high and it doesnt do anything except I said on pin 2 of the 74LS47 decoder if I disconnect the gnd it displays the zero. disconnecting 1 gives me mirrored 6. pin 6,7 bare do anything other than the display blinks a little.

What should i do next? for testing?

thanks,
barbaro

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
There's your problem. the inputs to the 74LS47 are NOT pins 2,3,6, and 7 -- they are 1, 2, 6, and 7.

Pin 3 is the lamp test function which displays 8 (all segments lit) when pulled low.

Check your circuit diagram (which appears correct in this respect).

#### barbaro

Jul 11, 2011
21
Hi Steve,

Sorry, I wasn't able to confirm this with you. I still having problem. In my earlier thread, I have mentioned that I did disconnect all the wire leading to the 7 segment which is really 2,3,6,7 from the counter 74HC192 IC and not the 74LS47 display decoder IC.

However, it's still not counting right. Following the correct pinouts from the counter IC to the decoder IC seemed to be not working for me.

How about the compatibility of the two IC's? is there any chance these two are not 100% compatible?

For some reason, I don't get any other figure other than 6,7 and 8 by randomly pressing B1 - up, B2 - down and B3 -Reset push button switches.

Could it be because there are wire that are loose withing the breadboard? I chacke the power supply is correct, to light the LED's is 9V and +5V connections between IC's.

Is 74LS193 possible to use as the counter? If so, could you hepl me with the schematic?

Thanks so much.

Barbaro

#### barbaro

Jul 11, 2011
21
Hi Timothy,

Could you shed light in here? I really need help in having this work out right. Could you please recommen somerhing like a simple schematic. I just need some kind of a counter that I want to use the 74LS47 decoder. Can I use switches as a counter and display the two digit 01 - 99.

Could you review the connections.

See attached images....the circuit doesnt really do the counting but, it display random numbers...i.e. 2, 6, 9, and 0 if you press reset.

Thanks.

Barbaro

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• Vaughan-20110722-00067.jpg
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Jul 11, 2011
21
more images...

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• Vaughan-20110722-00066.jpg
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#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
I will repeat an earlier suggestion that you have not yet followed up on...

Disconnect the wires leading from the counter to the 7 segment decoder.

Ground all the inputs to the 7 segment decoder. Does it display 0?

Take each input to logic high one at a time (just leaving them floating -- i.e. connected to nothing -- should work for testing). The decoder should give you the values 1, 2, 4, and 8.

then measure the voltage on the output of the counter. Are they all at 0V after you hit reset? Which pins are you testing (i.e. which pins do you believe are the outputs).

#### barbaro

Jul 11, 2011
21
Hi Steve,

Yes I did, please refer to the outcome on the last image that displayed "0". The decoder gave me the values 1, 2, 4, and 8.

First of all, is all my connections OK? I was testing pins 2,3,6 and 7 of the counter.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Sorry, for some reason I totally missed that post.

I think I am seeing things (or failing to see things)

OK, so you get 0 with al the decoder pins grounded, and 1, 2, 4, or 8 as you disconnect one at a time from ground. That indicates the decoder is working properly.

Next you need to confirm that after reset, all the counters outputs go low.

If they do not, check that your reset is wired to the correct pin and that you have really identified the outputs correctly.

The first thing to do is to get reset dropping all outputs low.

Check (and double check) with both the schematic and the datasheet that you have identified the correct pins. If in doubt, the datasheet is right.

I have to go out soon. I'll see if I can be more helpful and observant when I get back.

edit: re-reading your posts, I'm not sure if you are telling us that it displays random digits when you reset, or when you count (and 0 when you reset).

I suspect it displays 0 when reset, then "random digits"

My guess is that on the first count it displays 1, 2, 4, or 8. If it displays anything but 1, then you have the lowest order bit connected to the wrong input of the decoder.

Once that is working, the second count should show 2. If it displays 4 or 8 then your 2^1 bit is connected incorrectly.

you should then be able to get it to count 1, 2, 3, if the next count is 8 instead of 4, the 2^2 bit is wrong. Once that is correct, it should count correctly.

My suspicion is that some of the unusual displays are what the decoder gives you for counts 10 to 15.

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#### barbaro

Jul 11, 2011
21
Hi Steve,

Sorry for not getting back to you on the result of teh testing, I was off on vacation for 11 days and it's only now that I have to revisit teh project.

This time, I found out that my 7 segment is incorrectly connected to my decoder pinouts. My segment "d" and "e" were interchanged. So, I got that corrected.

Now, the counter up and down are OK by pressing S1 or S2 provided, it is counting only the add numbers - 1, 3, 5, 7, 9 and back to 1 after 9.

Is it possible because I haven't connected the other circuit yet for the second digit (decoder and counter)?

Could you please let me know.

Thanks,
Barbaro

#### barbaro

Jul 11, 2011
21
Hi Steve,

I hope everything is well with you.

I just got a suggestion from a friend to add a 4.7K pullup resistor to the A, B, C, & D (pins 1, 7, 2, & 6 off the '192). That may boost the HIGH levels up enough to make it count properly as in order i.e. 1, 2, 3, 4,.....9. I'm not sure if this would work but, can you please confirm?

Thanks,
Barbaro
__________________

#### barbaro

Jul 11, 2011
21
Hi Steve,

Forgot to mention, I disconnected the capacitors on my UP and DOWN switches. Is this causing the only add numbers counting?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Disconnecting the capacitors on the up/down switches may well cause the counter to count randomly (or appear to count randomly) because it may count many times as the switch bounces on make and/or break.

#### barbaro

Jul 11, 2011
21
Hi Steve,

I did all the test and it's all OK. The counter is working and counting from 0,1,,2,3,4,5,6,7 skipping 8 and then dsiplays 9. This is on the count-up switch. Also, this is when I disconnected the capacitor. I left the capacitor on count-down switch but it's only displaying 0, 2, and 6 but it's bouncing with the capacitor connected to it.

What else should I do to make the counting right for up and down and properly displaying the correct increments or decrements by ones.

Please teake a look at the current circuit images and let me know your best recommendation. could you let me know how to test the current voltages if that's what causing the problem? or did I connected the wires incorrectly on the reset and on the switches? Should I change the switches itself?

BTW, I used 47nF as the value of my switch capacitor.

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#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
If it skips 8 and counts 9 every time, I would suggest that you have the wrong pin connected to the 2^3 input of your decoder. Have you connected the carry output to it instead of the 4th bit?

Connect both switches like the one that works

edit:

1) pullup resistors are for connecting TTL to CMOS, not the other way around.
2) correct connections are pins 3,2,6,7 on the 192 to pins 7,1,2,6 on the 47. Check the last pair in particular (7 to 6)

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#### barbaro

Jul 11, 2011
21
Hi Steve,

I have all the connection correct. Like I said, I tested all the pins that they're connected properly and it's ok.

#### TBennettcc

Dec 4, 2010
292
1) pullup resistors are for connecting TTL to CMOS, not the other way around.

Steve, would you mind expanding on this with details to clarify? I've read about pullup resistors before, and while I understand why they're used, when to use them (always?) is a different story... I'm also not clear on the distinction between CMOS and TTL... is TTL +5VDC, while CMOS has a broad range of voltages it will work with? Is that the only difference?

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