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Author Topic: PIC -> or gate -> LCD ?  (Read 3270 times)

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Offline SilverHawkTopic starter

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PIC -> or gate -> LCD ?
« on: March 19, 2016, 02:32:42 pm »
Im having trouble understanding why are the (or gates) necessary ?, does it have to do with delay ?

Ive uploaded the datasheet for the ic , lcd , the pic im using is PIC18F46K20
« Last Edit: March 21, 2016, 02:58:18 am by SilverHawk »
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Offline ade

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Re: PIC -> or gate -> LCD
« Reply #1 on: March 19, 2016, 02:57:45 pm »
They're using it for level shifting maybe?  The PIC is at 5V and the LCD is at 3.3V.  That OR gate chip might be a 3.3V device that's 5V tolerant.
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Offline SilverHawkTopic starter

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Re: PIC -> or gate -> LCD
« Reply #2 on: March 19, 2016, 03:00:39 pm »
can you elaborate a little bit about level shifting , im a beginner and  i have no idea what that is.
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Offline SL4P

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Re: PIC -> or gate -> LCD
« Reply #3 on: March 19, 2016, 09:08:58 pm »
Quote from: SilverHawk on March 19, 2016, 03:00:39 pm
... have no idea what that is.
A *really* badly drawn schematic!
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Online mariush

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Re: PIC -> or gate -> LCD ?
« Reply #4 on: March 19, 2016, 09:29:06 pm »
If you have a microcontroller powered from 5v and you send a digital 1 on a pin, at the end of that pin you'll get 5v.
Problem is you may want to connect a device like a LCD display as shown in the picture which was designed to run on a lower voltage and will probably be damaged by 5v.

You work around that by introducing something between the microcontroller and the lcd display, a simple component that's powered from the lower voltage but  which has an input that can handle up the higher voltage on the input but outputs only as much as the chip's input voltage.

The other way is also possible, to shift from a lower voltage to a higher voltage, see for example http://electronics.stackexchange.com/questions/81580/step-up-3-3v-to-5v-for-digital-i-o for a detailed post with examples.
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Offline KL27x

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Re: PIC -> or gate -> LCD ?
« Reply #5 on: March 20, 2016, 12:06:44 am »
Quote
Im having trouble understanding why are the (or gates) necessary ?,
I am, also.

Badly drawn schematic aside...

I know of no reprogrammable PIC that cannot run down to at least 2.0V.
I know of no HD33780 LCD that cannot run on 5V.

Even if I needed to run the PIC on 5V and LCD on 0V, I would just put a 4.7K-10K resistor between each PIC output pin and LCD input pin. No pulldowns. No OR gate IC.

Maybe he needed a buffer to get the refresh rate from 60 Hz to 62 Hz.
« Last Edit: March 20, 2016, 12:09:11 am by KL27x »
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Offline SilverHawkTopic starter

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Re: PIC -> or gate -> LCD ?
« Reply #6 on: March 20, 2016, 12:41:56 am »
sorry about the schematic guys, i didnt draw it though , part of school project
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Online Zero999

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Re: PIC -> or gate -> LCD ?
« Reply #7 on: March 20, 2016, 11:05:20 am »
It doesn't give enough information, such as part numbers, especially for the gates.
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Offline danadak

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Re: PIC -> or gate -> LCD ?
« Reply #8 on: March 20, 2016, 12:57:54 pm »
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Offline SilverHawkTopic starter

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Re: PIC -> or gate -> LCD ?
« Reply #9 on: March 21, 2016, 03:17:16 am »
Thank you all for your answers

Ive uploaded the lcd and ic datasheet if you guys are curious
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