# Basic Circuit Question

Discussion in 'Electronic Basics' started by Jon, Jan 27, 2004.

1. ### JonGuest

Hey

I'm using a switch, 9V battery and an LED and I would like to have it
so the LED blinks (or any type of oscillation). The problem is I
don't want to get into ICs and such, since the 9V is my only source of
power (and I dont want to do a DC-DC conversion). is there any way to
do this with components like capacitors and resistors? (with time
constant stuff perhaps?)

2. ### Costas VlachosGuest

Resistors and capacitors alone won't be able to make an oscillator. The
reason for this is fundamental to electronic circuits and is mainly beacuse
R's and C's are passive components. You need to throw an active component,
such as a transistor, in the mix.

http://members.shaw.ca/roma/twenty-three.html

Costas

3. ### MonkGuest

yah you need at least a transistor in there,

google search -- R-C phase shift oscillator
-- transistor Colpitts oscillator
-- transistor Hartley oscillator (colpits is easier
only one inductor)
-- Pierce Crystal oscillator

or you could go with 2 9v batteries and a op amp if you wanted too
also i think that you could do a 555 timer as an astable multivibrator
with a 9v (i think it would run at 9) don't know the current draw on
them is so i dont know how long your battery would last tho.

cheers,

monk

4. ### John PopelishGuest

An LMC555 is perfect for this task, running directly off the 9 volt
battery.

The data sheet shows how to make an oscillator, figure 4 on page 5:

http://cache.national.com/ds/LM/LMC555.pdf

Connect the LED in series with a 1k resistor between the +9 volt line
and the output pin. or between the -9 volt line and the output pin.
The first is best for short pulses with longer time between, and the
second is better for long pulses with shorter time between.

Page 6 gets into the resistor and capacitor values needed versus pulse
time and pulse frequency. This chip costs less than a dollar and is
quite common. The LM555 is even cheaper and more common, but uses
more battery power.

5. ### Terry PinnellGuest

Here's a two-transistor circuit you could try.

http://www.terrypin.dial.pipex.com/Images/LEDFlasher2Transistor.gif

Experiment with the values of C1 and C2 to get the flash rate you
want.

6. ### Larry GreenGuest

Just buy a 'flashing' LED. They are available in a number of colours. You
will need to calculate the correct series resistor for it though.

Larry