Rikard Bosnjakovic wrote:
> To cut a long story short, for this project I have a relay that (with
> the help of a PIC) trigs on any voltage between 16-30VDC. The system
> will be powered using a 9 or 12V wallwart. Perhaps 5, if I manage to
> find one in my junkbox (where I found the relay). What I need to do is
> to increase the voltage up to the level where the relay triggers. It
> will be triggered about 4-5 times each day, and 10 minutes each time

What voltage do you need accross the relay when on, and what current does it
then draw?

> What I don't want to do is to use a high(er) voltage wallwart, because
> I expect that the energy consumed in standby will be higher, and this
> project will be plugged in 24 hours a day.

It will probably be easier and cheaper to make a buck regulator to run the
PIC from a higher voltage than to use a boost regulator to run the relay
from a lower voltage.  This is because the PIC will likely draw a lot less
power, so you can get by with a smaller and cheaper inductor.

> So basically, what I'm looking for is a way to raise the voltage. I've
> googled around and found things about "step up-converters" and
> "chargepumps".

You will likely need too big and expensive capacitors to make a charge pump
produce the current the relay needs.  You need a basic boost switcher.
Fortunately these are easy to make.  You may be able to use the PIC to drive
it directly, depending on what else the PIC has to do and which PIC it is.
I use 10F204 a lot for running simple switching power supplies.

> And the budget as well, that's why I cannot
> buy a 5V-relay.

But 5V relays are cheap and available.  By the time you build a boost
switcher, you've probably paid for most of the relay in $$ and a lot more in
hassle.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist