Powering 5v LCD from 3v?

[Haku]

I know a little (just a little) on how you can increase voltage through DC-DC boosting which has got me quite curious on one aspect of this DIY scientific wristwatch.

How is he powering a 5v LCD from a PIC being powered by a 3v watch battery?

Looking at the schematic it appears he's doing some rudimentary voltage boosting using PWM with diodes & a capacitor, is that right and can it be done with a Picaxe?

 

[erco]

You can find these little 5V "emergency chargers" on Ebay for $2 or so: http://www.ebay.com/itm/UNIVERSAL-MOBILE-PHONE-EMERGENCY-CHARGER-USE-ONE-AA-pec-/380358701400?pt=PDA_Accessories&hash=item588f253158

Takes one AA battery and boosts it to 5 V. It will quadruple (or better) the current draw. Might be good for power in a PicAxe one AA project.

 

[bluejets]

I know a little (just a little) on how you can increase voltage through DC-DC boosting which has got me quite curious on one aspect of this DIY scientific wristwatch.

How is he powering a 5v LCD from a PIC being powered by a 3v watch battery?

Looking at the schematic it appears he's doing some rudimentary voltage boosting using PWM with diodes & a capacitor, is that right and can it be done with a Picaxe?

Maybe a voltage doubler circuit...??

 

[eclectic]

See also tip #10 here:

http://ww1.microchip.com/downloads/en/devicedoc/40040b.pdf

There are some other excellent tips as well.

e

 

[Haku]

Thanks eclectic, that's the exact information I was looking for

 

[Haku]

Did some testing, 18m2 running at 4mhz, PWM output at 10khz with 50% duty cycle, 0.6v drop down diodes with 0.1uf & 10uf capacitors and I'm seeing these values on the output with no load:

3.3v = 6v
3v = 5.4v
2.5v = 4.44v
2v = 3.47v

This could be a useful little circuit, only needing a couple of capacitors and a couple of diodes. Schotky diodes should provide a higher voltage due to their lower drop down voltage.