Vee (negative supply) for LCD from PIC PWM by David Covick

Vee (negative power supply) (for LCD etc...) from PIC PWM

David Covick [dac@WEST.NET]

I designed this little circuit a few months ago using SPICE. Just vary the PWM and you are home free. You don't need any external negative voltage!! It produces negative voltage on its own using a positive voltage in a charge pumping type method off the PIC PWM.

The attached virus free jpg schematic will fill you in.

Have at it! Sample ref code:
Connect PORTC.2 of 16F877 to PWM IN.
Connect Vee on LCD to Vee Out.

'**************** LCD Display Negative Voltage ********************
'********************* 16F877 @ 20 MHz ****************************

PR2=255              ' Set PR2 to 19.53 kHz
CCPR1L=230           ' Set Pulse width - CCPR1L must be less than PR2.
                     ' Lower number(pulse width)=higher view angle
                     ' PR2 value is 100% duty cycle.
                     ' PR2/2 = 50% duty cycle.
TRISC.2=0            ' Set CCP1 bit as output
T2CON=%00000100      ' Timer on prescale is 1
CCP1CON=%00001100    ' Set PWM Mode
'******************************************************************

See

file: /Techref/microchip/pwmvee.htm, 1KB, , updated: 2009/9/28 16:17, local time: 2024/11/5 04:37,

^{3.22.217.45:LOG IN}

©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?

Please DO link to this page! Digg it! / MAKE!

<A HREF="http://linistepper.com/Techref/microchip/pwmvee.htm"> Vee (negative supply) for LCD from PIC PWM by David Covick</A>