blackie123
Posts: 23
Joined: Fri Jun 08, 2018 12:41 pm

Re: LCD display returning 5V

Tue Aug 14, 2018 9:41 am

The LED is connected to the same 5V pin as LCD.
If I disconnect the LCD's connections going to RPi (RS, EN, D4-D7) it turns off.
But if I disconnect just a 5V wire (connected to breadboard) the LED stays turned on.

I think that the voltage comes from one of the RPi's pins to the LCD? And then to the LCD's 5V input (through the LCD's circuit)?

blackie123
Posts: 23
Joined: Fri Jun 08, 2018 12:41 pm

Re: LCD display returning 5V

Tue Aug 14, 2018 9:51 am

I set all the pins to LOW and the LED powered off!
Won't the resistors use any current if the pins are set to LOW?

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davidcoton
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Location: Cambridge, UK

Re: LCD display returning 5V

Tue Aug 14, 2018 1:32 pm

Sorry, misunderstood your earlier post. Phantom powering is from Pi to LCD, not from a peripheral to the Pi. Setting all GPIOs low will obviously stop it, but why does it matter? 5V will presumably normally be connected and if the system is shut down, 5V will be removed from ther Pi.

The resistors (between GPIO out and ground) won't use any current if the GPIO is low.
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blackie123
Posts: 23
Joined: Fri Jun 08, 2018 12:41 pm

Re: LCD display returning 5V

Tue Aug 14, 2018 1:41 pm

OK. Thanks for help. Everything is working now.

Brandon92
Posts: 405
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: LCD display returning 5V

Tue Aug 14, 2018 2:28 pm

Maybe a little to late to the party, but the HD44780 (page 55) has indeed build in pull-up mos. And profide a maximum current of 250uA (page51).
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blackie123
Posts: 23
Joined: Fri Jun 08, 2018 12:41 pm

Re: LCD display returning 5V

Tue Aug 14, 2018 2:37 pm

Ok. But there is no problem connecting the 10K resistor to GND I think?

Brandon92
Posts: 405
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: LCD display returning 5V

Wed Aug 15, 2018 9:24 am

blackie123 wrote: Ok. But there is no problem connecting the 10K resistor to GND I think?
I think there is no problem. Because, when you calculate the maximum voltage that will be present across the resistor is (250uA*10k) 2.5V

blackie123
Posts: 23
Joined: Fri Jun 08, 2018 12:41 pm

Re: LCD display returning 5V

Wed Aug 15, 2018 9:35 am

Ok. Thanks.

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