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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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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 – shimofuri Jul 27 '12 at 13:48
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). – Wouter van Ooijen Jul 28 '12 at 10:07
Supplying power at a higher voltage. In beginner terms :-) – Mark Ingram Jul 28 '12 at 12:53
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possible duplicate of Arduino / Raspberry Pi: Voltage Converters and IO-Pins – Brian Carlton Jul 30 '12 at 23:08

3 Answers

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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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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. – 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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