How to use CD40109BE to level shift one input from 3v to 5v?

I want to use the Raspberry Pi's 3.3v GPIO pins to control whether a 5v LCD screen is on or off. The Raspberry Pi has a 5v pin but it cannot be turned on or off using Python or similar. Only the 3.3v GPIO pins can.

Therefore, to do this I want to use a CD40109BE level shifter (datasheet) to shift the GPIO pin's voltage from 3.3v to 5v but I'm not quite sure how to connect it up.

Here's a schematic of what I want to do with the chip:

simulate this circuit – Schematic created using CircuitLab

But how would I do it? What pins and components would I need to use? I tried the schematic from this answer but it didn't seem to work for me and I only want to use a single input and output.

Thank you

• Welcome to EE.SE, Billy. You need to include a datasheet link for the LCD so we know what type of input it has. Please edit your post to include it there. – Transistor Nov 27 '17 at 18:19
• Hello, the LCD screen does not have a datasheet but here is a link to the product. amzn.eu/6OWDXoW – Billy Nov 27 '17 at 19:09
• "I tried the schematic from this answer but it didn't seem to work" - that schematic should work if you put +3.3V on pin 1 and +5V on pin 16. Exactly how do you expect the output to turn the LCD on and off? (CD40109 output can only source ~0.5mA, so it could control a switch but can't supply power directly to the LCD). – Bruce Abbott Nov 27 '17 at 19:13

That is an TC1602A-01T display and the datasheet was found by searching for "1602 LCD datasheet".

The CD40109BE is designed for shifting logic-level signals. In your case you want to switch the backlight on and off. Reading the datasheet reveals:

Figure 1. Datasheet extract. Note the warning!

The CD40109BE is not suitable for switching 100 mA.

Figure 2. R1 limits the current to a safe value. Q1 allows switching from a 3.3 V GPIO. Source: 1602 LCD backlight LED.

$R_1 = \frac {V_{SS}–4.1}{0.1 }$

For a 5 V supply this would give R1 = 9 Ω. The nearest standard value is 10 Ω and this would be fine.

• Thank you. This seems to be working except for the fact that when the LCD screen is off, it is ~3v when it should be 0v. 3v still shows the backlight. (nb: My R1 is 100Ω because I don't have any 10Ω resistors) – Billy Nov 27 '17 at 20:59
• (1) "... it is ~3v when it should be 0v." What is? Please reference the schematic. For example, "I measure 3 V between A and GND when the GPIO pin reads 0.2 V." (2) Put 3, 4 or 5 x 100 Ω resistors in parallel. $R = \frac {100}{n}$ where n is the number of resistors. (3) What value is R2. (4) What transistor did you use? – Transistor Nov 27 '17 at 21:21