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Seven segment led scoreboard

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sparky72

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I am building a smaller version of a seven segment scoreboard that I built last year. The first board that I built is working great but I am having problems getting the second one to work properly. The components that I am using are the same as the first. They consist of a CD4093 Schmitt Trigger, MC14543B Latch Decoder, MC14553 BCD counter, and a ULN 2004 AN IC. driver chip. It is a multiplexed system using two PNP 2907 transistors. with a .001uf cap between the number 3&4 pin on the MC14553 and 10k resistors going to the transistor base. I guess before I get into a whole lot of detail, would anyone have any suggestions as to why the display only shows 2, 4, 6, 8, etc. No odd numbers. I have checked and double checked the circuit many times but cannot find the problem. The score board runs on 12 volts dc and the battery is fully charged.
Thanks in advance for any help I may receive. Lorne
 
A schematic would help. Sounds like the counter is getting double pulses. Could be you have some bits shifted left, though that isn't likely with a BCD counter that reads correctly otherwise.
 
Yes; schematic, please. Also what did you in fact build it on? PCB? Breadboard? Point-to-point?

Do you have a scope? (Just asking, in case we get to the point of wanting to look at pulses..)
 
Thanks for the quick response Video Warrior & duffy First of all I will answer your questions. The first circuit for my new scoreboard was a home made pcb. When finished, display only showed 2, 4, 6, etc. At that time, after a lot of checking I decided that it may have been a problem with the home made circuit board, so I decided to make the second one on a perf board from Radio Shack, using wire and solder tracks, which by the way, I used on the first scoreboard last spring, which is working great. In answer to your question, do I have a scope, the answer is no. I am just a retired senior citizen just getting in to this new found hobby, that I enjoy & the limit to my equipment at the moment, is a digital volt meter & a soldering iron. As you requested I have attached a couple of schematics relating to the project. The digital display is a common anode, seven segment display using 5 leds in each segment for a total of 35 leds per digit. The schematic does not show the ULN2004 driver. It is connected directly to the MC14543 latch decoder between the led resistors and the latch decoder. Pin 16 is vdd on the counter and latch decoder & pin 8 is vss on the ULN 2004AN driver. Hope this helps. Thanks again for any info you may give me. Lorne
 

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hi sparky,

Check that pin 9 to pin 5 connection is present and if present it is not grounded to 0V.:)

Thats the Q0 bit.
 
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Heh, that could be it. I assumed he meant it went 2 - 4 - 6... on every switch transition, but maybe he means every TWO switch transitions.

If that's the case, it could also be a blown driver on Q0 of the 14553.
 
Heh, that could be it. I assumed he meant it went 2 - 4 - 6... on every switch transition, but maybe he means every TWO switch transitions.

If that's the case, it could also be a blown driver on Q0 of the 14553.

hi,
If that connection is present, I would suggest he uses a DVM on that connection to see if it does change state on on ALTERNATE key presses.

Well Sparky, we are waiting to hear what you find.
 
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hi,
If that connection is present, I would suggest he uses a DVM on that connection to see if it does change state on on ALTERNATE key presses.

Well Sparky, we are waiting to hear what you find.

Every time I push the momentary switch it jumps 2 digits. I does not show odd numbers. It starts at the number 2 on the first push and proceeds 4, 6, 8, 10 etc. . Also the number 5 to 9 pins are not grounded. Thanks guys for the reply. Lorne
 
Hmm.. Well, sparky72 (and with no idea just where you are located, if it is Heating Season where you are) these days for those of us in the Northern Latitudes static discharge is sometimes an issue. The CMOS parts you list have gotten MUCH better than in the old days, but you can still blow something up with a big enough *ZAP*. Are you grounding yourself (and hopefully your work area) when you assemble these circuits?
 
Hmm.. Well, sparky72 (and with no idea just where you are located, if it is Heating Season where you are) these days for those of us in the Northern Latitudes static discharge is sometimes an issue. The CMOS parts you list have gotten MUCH better than in the old days, but you can still blow something up with a big enough *ZAP*. Are you grounding yourself (and hopefully your work area) when you assemble these circuits?

I do ground myself by touching a water pipe before I handle the ic's and I am standing on a rubber mat. However I am not connected to ground all the time. I had no problem blowing ic's on my first project using this procedure but I guess there is always a first time. Thanks for the input. Lorne
 
I don't think it's sparking arcs, Ted, if it was static it would never jump by exactly two every time. A blown chip doesn't sound right, either.

Also the number 5 to 9 pins are not grounded.

5 to 9 on what chip, Sparky?
 
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I don't think it's sparking arcs, Ted, if it was static it would never jump by exactly two every time. A blown chip doesn't sound right, either.



5 to 9 on what chip, Sparky?

Number 9 pin on the mc14553 chip goes to the number 5 pin on the MC 14543 chip. The number 5 pin on the MC14553 chip goes to the goes to the number4 pin on the MC14543 chip. The number 9 pin on the MC14543 goes to the Number7 pin on the ULN2004 driver chip which drives the a segments on the digital display.
 
Number 9 pin on the mc14553 chip goes to the number 5 pin on the MC 14543 chip. The number 5 pin on the MC14553 chip goes to the goes to the number4 pin on the MC14543 chip. The number 9 pin on the MC14543 goes to the Number7 pin on the ULN2004 driver chip which drives the a segments on the digital display.

hi,
Do you have a bench DVM.?
If yes, then connect the 0v of the DVM to the 0V rail of the pcb.
Set the DVM for 15Vdc, connect the +V of the DVM to the 9 to 4 wire.[Q0]
Press the clock push switch once [ to make it count up], note the voltage on the DVM for each switch press, it should go high and low alternately for each push.

When you do this test, sometimes when you press the count switch, hold it down, for say, for a couple of seconds. You just maybe getting a 2nd pulse on the switch release.

If you dont have a bench DVM, then use a LED with a series 1K0 resistor as the voltage/state indicator on the 9 to 5 wire.[Q0]

Where are you located.?
 
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Sure sounds like double clocking. Too bad no scope. The debounce ckt may need some tweaking. Since the first build was on proto board(Adds capacitance) maybe more capacitance is needed in the debounce on your current pcb version.

Check this good article.
http://www.ganssle.com/debouncing.pdf
 
hi,
Do you have a bench DVM.?
If yes, then connect the 0v of the DVM to the 0V rail of the pcb.
Set the DVM for 15Vdc, connect the +V of the DVM to the 9 to 4 wire.[Q0]
Press the clock push switch once [ to make it count up], note the voltage on the DVM for each switch press, it should go high and low alternately for each push.

When you do this test, sometimes when you press the count switch, hold it down, for say, for a couple of seconds. You just maybe getting a 2nd pulse on the switch release.

If you dont have a bench DVM, then use a LED with a series 1K0 resistor as the voltage/state indicator on the 9 to 5 wire.[Q0]

Where are you located.?

I would not be surprised if the C value of the meter might make the circuit start working.
 
hi,
Do you have a bench DVM.?
If yes, then connect the 0v of the DVM to the 0V rail of the pcb.
Set the DVM for 15Vdc, connect the +V of the DVM to the 9 to 4 wire.[Q0]
Press the clock push switch once [ to make it count up], note the voltage on the DVM for each switch press, it should go high and low alternately for each push.

When you do this test, sometimes when you press the count switch, hold it down, for say, for a couple of seconds. You just maybe getting a 2nd pulse on the switch release.

If you dont have a bench DVM, then use a LED with a series 1K0 resistor as the voltage/state indicator on the 9 to 5 wire.[Q0]

Where are you located.?

Hi ericgibbs I live in southeastern Ont. Canada. I do not have a bench DVM so I tried the led resistor method. I soldered a 1K0 resistor to the led. I powered up the circuit, placed the cathode of the resistor on 0V and the anode on the Q0 (9pin) then pressed the count switch. Nothing happened. The led did not light up. This seems to indicate to me that either the schmitt trigger or the MC14553B counter could be the problem. By the way, the master reset switch works bringing the display back to 0. Thanks for the input. Lorne
 
I would suspect your gate circuits after the pushbutton for double clocking. See the link I posted earlier on debounce. Are you using the same switches as your first model?

Try adding a 10k resistor between the normal open contact and gate input. Cap and pullup remain as is.
The reset ckt will not show debounce problem as it will reset multiple times without you knowing it. The other PB sw will care.
 
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By the way, the master reset switch works bringing the display back to 0. Thanks for the input. Lorne


hi,
Look at this image, I have used the spare gate on the 4093 as an oscillator, about 1Hz.
Disconnect the existing wire to pin 12 of the 14553 and connect 4093 pin 4 in its place.
This should auto pulse the counter at about 1Hz, it will prove the if the debounce is the problem or not.:)
 

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Very clever approach EG. Brilliant:)
 
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