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7 segment LED circut

Rick Whidden

Jul 24, 2015
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Jul 24, 2015
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I have 5 banks of 9 switches each. What I would like to do is if switch 3 on bank one is close then the corresponding LED would read 3, if switch 7 is closed on the same bank (switch 3 open) then the LED would read 7. Only one switch on each bank would be closed at one time. End result would be LED output (example) 38572. I am a beginner but competent.
 

Le Sy Hau

Jul 20, 2015
15
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Jul 20, 2015
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how many pins of each LED? Your LEDs are BCD type or normal type?
 

Le Sy Hau

Jul 20, 2015
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Jul 20, 2015
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I have not purchased any parts yet, looking for advise?
yeah, its different between BCD type and normal type, but I think you should use normal type because it is cheaper and more popular, and the circuit becomes more simple. I assumed that we use COMMON CATHODE LED. First, you need to connect left side of all switch together and connect them to VCC (5VDC or 12VDC). I made a table for you, follow the logic signal in this table, you can build your circuit ease. example: if logic signal is "not(1+2+3)", that's mean you have to OR signals from switch 1, 2 and 3 together, and then NOT them.Untitled.png
 

Rick Whidden

Jul 24, 2015
4
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Jul 24, 2015
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Very clear, I will be using 4 AA batteries for power with a diode before the circuit to lower the voltage to 5V. Sound easy enough. Thanks so much!
 

Le Sy Hau

Jul 20, 2015
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Very clear, I will be using 4 AA batteries for power with a diode before the circuit to lower the voltage to 5V. Sound easy enough. Thanks so much!
I think you shouldn't use AA battery for your circuit because the resistance of AA battery is quite high, and it's can not supply for long time. You can use Li-on battery, this is best choice for circuits which running on battery, or use 5V DC from USB port. And your 7 segment LED will need a strong power supply, so you can not use battery in this case, 5V DC from USB port is the best choice.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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7 segment displays use very low current. AA batteries would be fine. Most operate at just a couple of mA per segment.

What you need to do is wire up diodes from each switch to just light up the segments required. If you're clever, you can wire other contacts (if you have them, so that only one switch is active at any one time).

Fran describes the technique here. In this case, she uses a 4017 which has only one output active at a time.

You could simply wire up your switches as if they were the 10 outputs of the 4017, but turning on 2 or more would likely result in something undesirable. There are ways around this, but you assert that it can't (or won't) happen.
 

eetech00

Nov 17, 2014
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Nov 17, 2014
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I have 5 banks of 9 switches each. What I would like to do is if switch 3 on bank one is close then the corresponding LED would read 3, if switch 7 is closed on the same bank (switch 3 open) then the LED would read 7. Only one switch on each bank would be closed at one time. End result would be LED output (example) 38572. I am a beginner but competent.

Does it have to have 5 banks of switches?

How about one bank of switches (1-9), a set and reset button, and five LED displays?

You would set five switches, then press the set(or reset) button.
 
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