Basic Electronics Help Needed !!

[Ferret_san]

Hi Guys. Hoping someone here with some basic electronics knowledge can
help me out. My nephew is doing a class project and wants to make a simple
working traffic light.

Because I have a very limited understanding of electronics <cough> none
<cough> I'm hoping someone can show me the wiring diagram that I'd need
to put together.

Basic plan is to use 3 flash light bulbs and hook them up to a simple 3
way slide switch and battery pack (2 AA batteries or 9 volt ?),so the left
position illuminates the red light, the middle illuminates yellow, and the
right position illuminates the green.

A further on/off switch will also be included for the power.

Anybody feeling generous that can help me out with the wiring ?

Nothing fancy, just something simple enough for him to explain how it works,
and how it was wired.

[Tamago]

here's a ladder logic wiring diagram

http://i44.tinypic.com/acftk.jpg

[highwaypass]

i forgot how to do it,but once i made it on my junior high school project.
Why don't your nephew just buy the knock down one?

[highwaypass]

hope this will help you.
http://img39.imageshack.us/img39/2561/basicstuffjugac.th.jpg (http://img39.imageshack.us/my.php?image=basicstuffjugac.jpg)

CMIIW :biggrin:

[Ferret_san]

Sorry Tamago, I can't really translate the ladder logic diagram.
Any chance you could simplify it on the diagram I posted ?
And unfortunately, the 2nd on/off switch is a necessary evil I'm afraid.

[CTScott]

Here you go:


24520

[Ferret_san]

Here you go:

You're a good man. Thank you sir !

[jambo101]

Get your nephew some extra brownie points for creativity and run it off solar power.

[firemachine69]

FYI, you're going to need a resistor with those LEDs.

[GeneW]

Here you go:


24520

I think 390 ohms is a bit light, no pun intended, with an LED and a 9 volt source. I've seen about two to three volt drops on average with an LED, which gives you from 15mA to 18mA current with a nine volt battery and 390 ohm resistor. That's a wee bit high for an LED. You can do it but they get hot and won't last long. Also drains the battery faster.

Keeping that current around ten mA would run the LEDs cooler... I'd recommend a 560ohm resistor, which would give you a more gentle 11mA to 12.5mA range, assuming a 3 to 2 volt drop across the LED.

I used to use 470ohm resistors with 5 volt sources and LEDs... I like to keep things on the low to middlin end to preserve function and reduce heat on working parts.


Gene

PS

If someone can scan in the LED's spec sheet we can do a better job of calculating a good current limiting resistor for this project.

[CTScott]

5mm axial lead LEDs are rated for 20mA or greater.

Red: forward voltage = 2.2V, forward current = 30mA
Green: forward voltage = 3.5V, forward current = 25mA
Yellow: forward voltage = 2.0V, forward current = 30mA

The 390 ohm resistors are fine for all three LEDs.

[GeneW]

5mm axial lead LEDs are rated for 20mA or greater.

Red: forward voltage = 2.2V, forward current = 30mA
Green: forward voltage = 3.5V, forward current = 25mA
Yellow: forward voltage = 2.0V, forward current = 30mA

The 390 ohm resistors are fine for all three LEDs.

Typical or Absolute maximum ratings?

Gene

[CTScott]

Typical or Absolute maximum ratings?

Gene

Typical. Absolute max is 100mA for all.

[GeneW]

Typical. Absolute max is 100mA for all.

Don't buy it. I've seen Max If as low as 50mA and even 30mA for some LEDs. Depends upon the manufacturer, lead heat conductivity and other factors.

I think we could both agree that whoever is building this thing better take a moment to read the If figures on the cut sheet. If not they could experience untoward failures.

Been there, done that....

Gene