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### Topic: LED problem (Read 3017 times)previous topic - next topic

#15
##### Jan 20, 2013, 05:47 am
Put the 01, 10, 11 as address bits into different logic - like a 74xx138, 74xx139 - selected out (#1, 2, 3) will go low, pull one cathode low.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### pranoy

#16
##### Jan 22, 2013, 05:45 pm
I want the LED to be ON one at a time with the ouputs ( 01,10,11)

There is only one 220 ohm resistor at one of the output pins.

I don't have enough pins so i have to go with 2 pins itself.

the ? is something i got from chatting in fb.

#### Grumpy_Mike

#17
##### Jan 22, 2013, 08:46 pm
Quote
There is only one 220 ohm resistor at one of the output pins.

You need another on the output of the logic gate.

#### pranoy

#18
##### Jan 23, 2013, 03:16 am
this is a fair ckt dgm with only one yellow LED

#### pranoy

#19
##### Jan 23, 2013, 03:23 am
thanks mike

but i tried it in a 2 way traffic scenario. but still the yellow light turns ON when Red comes in one of the tracks

#20
##### Jan 23, 2013, 04:08 am
What is IC1?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#21
7408 and IC

#### pranoy

#22
i meant AND ic

#23
##### Jan 23, 2013, 04:33 am
What does it do?
The LEDs can all be driven thru the IO pins shown:

D1 = 1, D0 = 0 turns on LED1
D1 = 0, D0 = 1 turns on LED2
D1 = D0 turns LED1 & LED2 off
same for 3,4  5,6  7,8
What's the AND gate do that couldn't be done with another IO pin instead?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Grumpy_Mike

#24
##### Jan 23, 2013, 12:47 pm

this is a fair ckt dgm with only one yellow LED

Regarding that diagram, the pins that go through a resistor to the LEDs should not be connected to the input of the AND gate, this should be connected directly to the arduino. I suspect that it is this that is causing a problem because the current flowing through that resistor is holding the input to the AND high and thus keeping the yellow on, which still needs its own series resistor.

#### pranoy

#25
##### Feb 02, 2013, 02:49 am

AND gate is for turning LED 3 ON D0-1 & D1-1

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