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I have an LCD screen which expects power from a 5V line, but I want to hook it up to my Raspberry Pi's GPIO pins which only supply 3.3V. What equipment do I need to increase the voltage from 3.3V to 5V?

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    \$\begingroup\$ Are you asking about how to supply power at a higher voltage OR are you asking about how to shift signals to a higher (logic) level? Supply vs Signal \$\endgroup\$
    – shimofuri
    Jul 27 '12 at 13:48
  • \$\begingroup\$ If you don't read from the LCD you might well get by with a direct connection (except of course for the power): the HD44780 datasheet states 2.4V as lowest level for a logical one input. (I assume you use a standard HD44780 character LCD). \$\endgroup\$ Jul 28 '12 at 10:07
  • \$\begingroup\$ Supplying power at a higher voltage. In beginner terms :-) \$\endgroup\$ Jul 28 '12 at 12:53
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    \$\begingroup\$ possible duplicate of Arduino / Raspberry Pi: Voltage Converters and IO-Pins \$\endgroup\$ Jul 30 '12 at 23:08
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If you only need to send data to the LCD you can use HCT buffers. HCT is TTL-compatible HCMOS, so made to work at 5V, but instead of needing 0.6 Vcc input for a high level (or even 0.7 Vcc) it can do with TTL levels, i.e. 2.4 V for a high level.

The 74HCT241 is an octal buffer.

For status and other unidirectional lines from the LCD you can use a resistor divider to scale the 5 V down to 3.3 V. A 10 kΩ resistor in series with a 20 kΩ gives you 3.3 V out for 5 V in.

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If you want to interface 5V and 3.3V logic you will need a level shifter. Maxim has a good app note on this here: http://www.maxim-ic.com/app-notes/index.mvp/id/3007

For I/O lines make sure your chosen level shifter is bi-directional.

You will not be able to power your 5V LCD from the 3.3V Raspberry Pi without something like a boost converter, or use a separate power supply.

MAX3370

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    \$\begingroup\$ The MAX3370 is more than 2 dollar in 1s, and he may need quite a few of them if the LCD has a parallel interface. \$\endgroup\$
    – stevenvh
    Jul 28 '12 at 5:16
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Since you are looking to power it, the GPIO pins are current limited. You would be better off using a single 5 V power supply to power both the Rasberry Pi and the LCD. It would need to supply the current to the Rasberry Pi (700 mA), plus however much the LCD needs.

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This question was researched by user pygmalion on the RPi forums, and the findings were that for some LCDs, there is a way to switch them between 5 V and 3.3 V logic and between serial interface and parallel interface on the back side of their PCB (source).

This includes JLX LCDs based on the ST7565 LCD controller and sold on the Aliexpress.com site. When you have to indicate which logic voltage you want, it seems to be an indicator that the device will be configured by the seller before shipment. I just looked, and still found such LCDs around (example). Maybe yours also has this capability.

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