NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Basic Electronics » Dimming LCD Problem

May 01, 2009
by paulip
paulip's Avatar

So I solved my transitor/relay problem on the other topic on this board...now I have a new one....but its related to the previous problem....

I have PB3 out of the microcontroller triggering a transistor and moving a relay...in test mode its powering 2 LEDs 1 is just a "control" which goes from PB3 just to an LED so that i can know if the pin is powered.

Then a 2nd one through the transistor and the relay.

When trigger PB3, the LCD dims...the more LEDs...the dimmer it gets....I have no diodes anywhere in the system...but i have this dimming problem with or without the relay...just the more LEDs the dimmer the LCD goes.

What can i do to fix this?

thanks

May 01, 2009
by MacGyver
MacGyver's Avatar

Are you powering from 9v battery? it sounds like too much current is being drawn causing voltage to drop below the 7.5v that the 7805 regulator requires to keep 5v through the rest of the system.

You could either wire resistors with the LED's to reduce the current they draw or use a wall DC adapter so you won't run out of current.

May 02, 2009
by paulip
paulip's Avatar

ok..thanks..yeah..9v battery....if thats all normal...that's great..just didnt want to hear that i wired something wrong...

-p

May 02, 2009
by mrobbins
(NerdKits Staff)

mrobbins's Avatar

Also take a look at this thread which describes the issue in more detail and also talks about possible solutions, including:

  • resistor in series with LED
  • software PWM to reduce the average current
  • run from wall DC adapter

Mike

May 03, 2009
by MacGyver
MacGyver's Avatar

Sparkfun has a nice 9v 650mA switched power supply, my multimeter reads it running at a constant 9v very reliably. They have a 5v / 1A one as well but I wanted the flexibility of being able to running 9v for certain applications as well.

They have a barrel jack to JST connector as well if you don't want to strip the power supply directly, works great so far with my nerdkit.

Found here: http://www.sparkfun.com/commerce/product_info.php?products_id=298

May 06, 2009
by paulip
paulip's Avatar

Wow..thanks...yeah..very useful information.

-p

Post a Reply

Please log in to post a reply.

Did you know that NerdKits make a great parent/child activity? Learn more...