Step down from 5V to 0V and then to 5V again

Thread Starter

manorius

Joined Apr 28, 2009
5
Hi,

I'm new to this forum and quite new to the electronics,
the only circuits I have created from scratch are relies
with 555 timers for my art projects, so please have some understanding
for my lack of knowledge :).

For a project I have a 5V LED and I would like to make a very small
circuit maybe one microchip big (space is an issue), to turn gradually on and then off (like the mac led when on sleep mode). Is there a chip that I can use to achieve this or is there a schematic for a small circuit that I could follow?

Thanks a lot!
 

thingmaker3

Joined May 16, 2005
5,083
Welcome to AAC!!:)

Just a stray thought... The 556 is a single chip with two 555 timers on-board.

IF...

If both timers were configured as astables, one fairly slow and one rather fast,

AND

and the capacitor voltage of the slow one (on either "Trigger" or "Threshold") were connected to "Control Voltage" of the fast one one...

...wouldn't the output of the fast one be pulse-width-modulated by the slow one's charge-discharge curve? Thereby making any LED hooked to it gradually dim and brighten alternately?
 

KMoffett

Joined Dec 19, 2007
2,918
Probably the smallest would be an 8-pin PIC, or other μcontroller, outputting a swept PWM, driving your 5V LED...battery, μcontroller, bypass capacitor, and the LED. The battery(s) will be the biggest component, and depends on how bright you want the LED to shine.

Ken
 

KMoffett

Joined Dec 19, 2007
2,918
I play with PICAXEs. They're Microchip PICs with a built-in interpreter. The 8-pin "08M" is about $3.50 and requires only a 3-wire serial cable and two resistors to program, with a free BASIC language editor/simulator on a PC. Their forum is very active and helpful: http://www.picaxeforum.co.uk/ Search there on: fading led. It's already been done.

Ken
 
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