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BOB-12009

P1-P3P4-P5
Bi-Directional Logic Level Converter Hookup
Guide
Introduction
Do you have a 3.3V I C or SPI sensor that might go up in smoke if
connected to a 5V Arduino? Or a 5V device that needs a workaround to be
compatible with your 3.3V Raspberry Pi, Arduino Due or pcDuino?
To get over this obstacle you need a device that can shift 3.3V up to 5V or
5V down to 3.3V. This is called logic level shifting. Level shifting is a
dilemma so common we designed a simple PCB assembly to make
interfacing devices a little easier: the Bi-Directional Logic Level Converter.
Though they’re share the same shape and size, this bi-directional logic
level converter shouldn’t be confused with the more “uni-directional”
version. This converter can pass data from high to low and/or low to high on
all channels. It’s perfect for level-shifting between devices that are sharing
a data wire, like I C or a one-wire interface.
Covered In This Tutorial
In this tutorial we’ll take an in-depth look at the Bi-Directional Logic Level
Converter. We’ll examine the schematic and board layout – explaining what
each pin on the board does. At the end we’ll go over some hookup
examples to show how you might hook the board up for various interfaces.
Suggested Reading
• Logic Levels
• How to Use a Breadboard
• What is an Arduino?
• How to Solder
• Working with Wire
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Board Overvie
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If you take a peak at the board’s schematic, you’d find that the bi-directional
logic level converter (let’s shorten that to BD-LLC) is actually a very simple
device. There is basically one level-shifting circuit on the board, which is
repeated four times to create four level-shifting channels. The circuit uses a
single N-channel MOSFET and a couple pull-up resistors to realize bi-
directional level shifting.
The bi-directional level-shifting circuit used on all four channels of the BD-
LLC.
Through some semiconductor magic, this circuit can shift a low voltage
signal to high and/or shift a high-voltage signal to a low voltage. A 0V signal
on one end remains a 0V signal on the other. For a complete analysis of
this circuit, check out this excellent Philips Application Note AN97055.
The Pinout
There are 12 total pins on the BD-LLC – two parallel rows of six headers.
One row contains all of the high voltage (e.g. 5V) inputs and outputs, the
other row has all things low voltage (e.g. 3.3V).
The pins are labeled on both the bottom and top sides of the board, and
organized into groups. Let’s look closer at some of the pin groups:
Voltage Inputs
Page 2 of 5
The pins labeled HV, LV, and two GND’s provide high and low voltage
references to the board. Supplying a steady, regulated voltage to both of
these inputs is required.
The voltage supplied to the HV and GND inputs should be higher than that
supplied to the LV side. For example, if you’re interfacing from 5V to 3.3V,
the voltage on the HV pin should be 5V, and the voltage on LV sould be
3.3V.
Data Channels
There are four separate data channels on the BD-LLC, each capable of
shifting data to and from high and low voltages. These pins are labeled
HV1, LV1, HV2, LV2, HV3, LV3, HV4, and LV4. The number at the end of
each label designates the channel of the pin, and the HV or LV prefix
determines whether it’s on the high or low side of the channel.
A low-voltage signal sent in to LV1, for example, will be shifted up to the
higher voltage and sent out HV1. Something sent in HV3 will be shifted
down and sent out of LV3. Use as many of these channels as your project
requires. You don’t have to use every single one.
Keep in mind that these level shifters are purely digital. They can’t map an
analog voltage from one max voltage to another.
Hookup Examples
Assembly
Before you can plug the converter into your system, you’ll need to solder
something into it. There are a lot of options here. You could solder straight
male headers in, and plug it right into a breadboard. Or perhaps you want
to solder wires directly into it. Pick an assembly method that melds with
how you intend to use the board.
Once your BD-LLC is soldered up, it’s time to hook it up. Your hookup will
probably vary depending on which communication interface you’re using.
Below we’ll show how to hook the level converter for three of the most
common communication protocols.
Using the BD-LLC for Serial
Although you won’t be taking advantage of the BD-LCC’s bi-directional
abilities, it’s perfectly fine to use the board to shift serial communication.
Serial usually requires two signal wires – RX (receive) and TX (transmit) –
which both have a defined direction. These signals can be passed through
any of the four channels on the BD-LLC.
Let’s say, for example, you want to hookup an Electric Imp Breakout Board
(which has a 3.6V maximum input voltage) to an Arduino Uno via their
UARTs. Here’s one possible hook up:
Page 3 of 5
P1-P3P4-P5

BOB-12009

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Manufacturer:
SparkFun
Description:
Daughter Cards & OEM Boards Logic Level Convert Bi-Directional
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