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Character LCD

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AtomSoft

Well-Known Member
Hey guys i was woundering... Anyone know where to buy 2x16 Character LCD but rated for 3V operation?

I own a couple 5v 2x16 LCDs ... i was thinking of making a booster from 3v to 5v... Do you think its worth it? Or should i just get 3V displays?
 

Sceadwian

Banned
Have you tried running them at 3 volts to see how stable they are?
 

dougy83

Well-Known Member
assuming you're using a ucontroller: if you have a spare output pin (one of the PWM pins would be simplest) you can make a capacitor multiplier with a couple of diodes and caps. The lcds generally only draw a mA or so
 

dougy83

Well-Known Member
The current through a cap is I = CVf

But I think you'll find it easier to just run a sim or do some trial and error until you get an output with the right voltage and sufficiently small ripple. Increasing the frequency will allow for greater output current, but will be limited by the IO pin output drive capabilities.

Circuit attached for reference.
 

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dougy83

Well-Known Member
I'm not sure; I don't use proteus. I would think so though.

Just remember to connect a load to the output to see what the droop & ripple will be with a load (i.e. the lcd).
 

AtomSoft

Well-Known Member
proteus does it well :D the f=voltage seems to forever rise. Even when i lower the rate at which i pulse..

Im assuming i can use this meathod and when i find a suitable speed i can use a cheap 555 timer to accomplish the same speed (pulse) and control it with that....
 

dougy83

Well-Known Member
proteus does it well :D the f=voltage seems to forever rise. Even when i lower the rate at which i pulse..
Forever? it shouldn't ever rise past 6V.

Im assuming i can use this meathod and when i find a suitable speed i can use a cheap 555 timer to accomplish the same speed (pulse) and control it with that....
A 555 timer doesn't have a rail-rail output, so unless you use a CMOS version you'll need to increase the number of multiplier stages; but otherwise, yes you could use a 555.

If you have a spare IO pin it can be used for free and will be able to supply the required current for an LCD (I'm assuming you use PICs).
 

dougy83

Well-Known Member
heh but i have to pules it constant which will require hardware PWM or software but will kill the power when i have to do another task.

If you don't have a hardware PWM or timer output you can use a timer interrupt.

e.g. to toggle portb.0
Code:
   org 4   ; the ISR
   btfsc PORTB,0
   goto $+3
   bsf PORTB,0
   reti
   bcf PORTB,0
   reti
It'll only use ~10 cycles per toggle which is almost nothing.
 

AtomSoft

Well-Known Member
heh yeah im toggling from RD6.. on actual circuit it turns my 2.5 volt to alittle above 5 which is awesome!!!!

But i need to get a new pot for contrast control.. for some reason my doesnt work using this meathod. I assume because the current is less anyway. heh i have a 5k pot i think. ill get a 100ohm or something heh thanks alot i learned something new :D
 

AtomSoft

Well-Known Member
Here is my schematic so far. But in real work LCD doesnt work because of contrast heh

(i think its the resistor (POT) tho)

boost-jpg.34594
 

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dougy83

Well-Known Member
Is the pot drawing too much current from the 5v supply?
 
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