Bi-Directional Logic Level Converter Hookup Guide Datasheet by SparkFun Electronics

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Bi-Directional Logic Level Converter Hookup
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
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-
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
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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
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
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:
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Make sure LV is powered at 3.3V, and HV is at 5V. Double-check that the
channels match up, and a-shifting you will go! You’ve even got two extra
channels to shift as you please.
Using the BD-LLC for SPI
The BD-LLC’s four channels are a perfect match for most SPI
communications. SPI usually requires four wires: MOSI (master out, slave
in), MISO (master in, slave out), SCLK (serial clock), and CS (chip select).
These four wires can each be routed through a channel on the BD-LLC.
For example, if you wanted to connect an Arduino to an ADXL345 Breakout
Board, which has an operating range of 2.0-3.6V, here’s how the BD-LLC
could be spliced in:
Since each of the channels on the BD-LLC are bi-directional any of the four
SPI lines can go through any of the BD-LLC’s four channels.
Using the BD-LLC for I C
I C is the communication standard where the BD-LLC really shines,
because it requires that both data and clock signals – SDA and SCL – be
bi-directional. Each of those lines can be passed through any of the BD-
LLC’s level-shifting channels.
For this example, let’s keep using the ADXL345 breakout but instead swap
over to the I C interface. We can even add another I C device…how about
the L3G4200D Gyroscope Breakout. Since I C is only a two-wire interface,
we have room on the BD-LLC to fit in a couple of extra signals, like the
interrupt outputs from each board
The two 3.3V I C devices can both share the same level shifted SDA and
SCL lines. Even more I C device can be added, as long as they have
unique addresses.
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Resources & Going Further
Here are some resources related to the LLC and level-shifting in general:
Bi-Directional Logic Level Converter Schematic
Bi-Directional Logic Level Converter Eagle Files
Bi-Directional Logic Level Converter GitHub Repo
Philips AN97055 – An awesome application note covering bi-
directional level shifting circuits.
Going Further
If you’re looking for a place to use the LLC, these tutorials might spark
some ideas:
Electric Imp Breakout Hookup Guide – The Electric Imp works at
3.3V max, so if you interface it with any 5V systems you may need
an LLC.
Getting Started with pcDuino – The pcDuino is another 3.3V-based
system. This is a powerhouse compared to the Electric Imp, though.
It can run Linux or Android, and has all sorts of awesome
Using the Arduino Pro Mini 3.3V – If you want to stick with Arduino,
and want to use 3.3V sensors, consider using an Arduino that runs at
3.3V. That way you won’t even need to bother with an LLC!
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