Logic Gate Problem

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thestudio

Well-known member
Joined
Jul 17, 2004
Messages
351
Any help on this gate problem. I can do this with a couple AND gates w/o Yellow but another Red but how can I accomplish with the extra Yellow logic :?: Is there a way with more gates or do I need a decoder 74LS145 :?: When 1 1 0 is selected only the Yellow LED will light :roll:

Logic.............LED Color

0 0 0 Red
0 0 1 Red
0 1 0 Red
0 1 1 Red
1 0 0 Red
1 0 1 Red
1 1 0 Yellow :shock:
1 1 1 Green
 
[quote author="thestudio"]Any help on this gate problem. I can do this with a couple AND gates w/o Yellow but another Red but how can I accomplish with the extra Yellow logic :?: Is there a way with more gates or do I need a decoder 74LS145 :?: When 1 1 0 is selected only the Yellow LED will light :roll:

Logic.............LED Color

0 0 0 Red
0 0 1 Red
0 1 0 Red
0 1 1 Red
1 0 0 Red
1 0 1 Red
1 1 0 Yellow :shock:
1 1 1 Green[/quote]

Are you actually lighting LEDs or do you need to accomplish this using logic ICs? You could alternately do some tricks with discrete transistors and resistors probably using less parts.

As Wayne pointed out... Red is Not_Yellow and Not_Green... so basically you need one decision to steer LED current for red or not_red, and then another if not_red, to steer between yellow and green LEDs.

JR
 
If you drive the LEDs with anodes to + and pulling down on cathodes through an R, I see a way to do it with a quad two-input NAND and one AND function. The AND could probably be done with two diodes and a pullup R if the logic is high enough voltage to shrug off the diodes not quite pulling to ground.
 
[quote author="bcarso"]If you drive the LEDs with anodes to + and pulling down on cathodes through an R, I see a way to do it with a quad two-input NAND and one AND function. The AND could probably be done with two diodes and a pullup R if the logic is high enough voltage to shrug off the diodes not quite pulling to ground.[/quote]

I'll see that and raise you, "I can do that with 3 NPN transistors and about 8 resistors." :cool:

JR
 
I'm using 5v LED's so my thinking was to use pull up resistors to save me from drawing to much from the IC :roll:

LED"S model 557 that I'm using............. http://www.dialight.com/

http://www.alliedelec.com/Images/Products/Datasheets/BM/DIALIGHT/Dialight_Actives-and-Passives_5110037.pdf

557-1502-203 Red 80ma/5v
557-1602-203 Yellow 80ma/5v
557-1702-203 Green 16ma/5v
 
I have a CircuitMaker file but I don't know how to upload :?:

Thinking of adding a flasher circuit for the Yellow :idea:
 

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