# need help with low voltage led circuit

Discussion in 'Electronic Basics' started by Tgriff346, Sep 28, 2004.

1. ### Tgriff346Guest

I need to build a board with painted animals( got it) with led eyes that light
up at night. I've tried to wire it up, but the led bulbs keep burning out. I am
using a 9 voltbattery. Any wiring suggestions?

2. ### Jonathan KirwanGuest

If LEDs are burning out, it's almost certain to be your circuit. Perhaps you
have no current limiting for the LEDs against the 9V source? But none of us are
psychic, so what's the circuit you are currently using?

Jon

3. ### John FieldsGuest

---
Connect one 390 ohm quarter watt resistor between each LED and the
battery.

View with a fixed pitch font like Courier:

+---[390R]---[LED>]---+
| |
+---[390R]---[LED>]---+
| |
. .
. .
. .
| |
+---[390R]---[LED>]---+
|+ |
[BATTERY] |
|- |
+---------------------+

4. ### John LarkinGuest

Just two led's? Connect them in series, with a resistor in the
circuit.

Battery+-------resistor------led1------led2-------battery-
A K A K

A = led anode
K = led cathode

try 470 ohms for the resistor to start. The lower the resistance, the
brighter the led's and the shorter the battery life. Don't go below,
say, 150 ohms. The limiting case is R=0, infinite brightness, dead
LED, which is what you're doing now.

John

5. ### Peter BennettGuest

You need a current limiting resistor in series with each LED -
something around 1000 ohms should be OK (the value is not critical -
lower resistance gives more current, and a brighter LED).