SparkFun Electronics - Logic Level Converter

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Product Info

Logic Level Converter

sku: BOB-08745

Description: If you've ever tried to connect a 3.3V device to a 5V system, you know what a challenge it can be. The SparkFun logic level converter is a small device that safely steps down 5V signals to 3.3V and steps up 3.3V to 5V. This level converter also works with 2.8V and 1.8V devices. Each level converter has the capability of converting 4 pins on the high side to 4 pins on the low side. Two inputs and two outputs are provided for each side.

Bread board friendly! Can be used with normal serial, I2C, SPI, and any other digital signal. Does not work with an analog signal.

The level converter is very easy to use. The board needs to be powered from the two voltages sources (high voltage and low voltage) that your system is using. High voltage (5V for example) to the 'HV' pin, low voltage (2.8V for example) to 'LV', and ground from the system to the 'GND' pin.

Pins are labeled as Inputs and Outputs. These are relative to the board. A digital one going into the RXI pin on the 5V side will show up on the RXO pin on the 3.3V side as 3.3V. A digital one going into the TXI pin on the 3.3V side will show up on the TXO pin on the 5V side as 5V.

Dimensions: 0.5x0.6"

Documents: Schematic

Pricing

	123 in stock backorder allowed

$1.95	price
$1.76	10-99 (10% off)
$1.56	100+ (20% off)

	quantity

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Comments

17 comments

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	by Syvwlch +3.1 \| August 16, 2008 at 8:23 AM +0.5
Hi, and thanks for all the good work. One question on this logic level converter: If I want to use this to connect a 5V processor to a 3.3V I2C sensor, can I connect one pin of the processor to the SDA pin of the sensor with both a TXI-TXO and a RXO-RXI line in parallel, and then switch that processor pin from input to ouput as required? If not, what do you recommend I do?

	by Quazar +65 \| September 30, 2008 at 11:41 AM 0
I think you can do that with this board. You'll need to use the two "TX" channels, (the ones with the MOSFETs), since I2C requires bidirectional I/O for both lines. There is a good appnote on the subject here.

	by okie +4.3 \| October 20, 2008 at 3:34 PM +0.3
If you're working with up above about 1MHz clocks, watch out for those resistor dividers. They'll attenuate your signal.

Dale

+6.8

| December 12, 2008 at 10:49 AM

While I am a novice, I am learning & appreciate feedback if what I am writing is incorrect.

1. The Tx lines are bidirectional. HUGE selling point & important for people using protocols like I2C. The Rx lines are unidirectional; only 5 to 3.3v

2. The Rx lines are not designed well for two reasons:

a) The resistors to generate a 3.3v output low side should be 10k R1 and ~20k R2. As is, the two 10k resistors split the voltage 50% resulting in approx 2.5v low side. This is outside the acceptable window for many 3.3v part like the LIS302DL sold on this site.

b) The two grounds on the breakout are common to each other. If the two ground were NOT common, then a user likely myself could be another resistor in series with the R2 on the breakout to adjust the low output voltage on each channel. Since however, they are common this is not easily possible because now current can flow between channels between the internal R2 and an external R2 in series.

I recommend posting portions of all the above for the benefit of your customers. And consider 2 for a future rev of the breakout.

	by cyberthom +1.5 \| February 4, 2009 at 3:28 PM 0
thanks for the explanation.. this is exactly whats going on.. i was wondering about the 50% split on RX the lines myself.. and just to clarify - you can use one I2C device with one of these.. both, SDA and SCL lines have to be wired up using the two TX lines of this board..

	by Dale +6.8 \| December 12, 2008 at 10:54 AM +0.3
The example table in the breakout schematic has a column LV. This leads the reads to believe that LV has some affect on the Max output. It doesn't. Its not even connected to the circuit. I recommend removing that column for clarity.

	by gke +2.2 \| April 15, 2009 at 5:40 PM 0
Neat product. Perhaps add a 3.3V regulator footprint. I am using the board between a LOCOSYS GPS unit and a 5V PIC and currently have two diodes to get about 3.8V from the 5V line - not ideal.

	by bengineerd +1.9 \| April 20, 2009 at 12:52 AM 0
Why not just make a breakout board for the TI TXB0108 and/or TXS0108E? 8 Bidirectional level shifting lines, and the chips are only $2 each.

	by Bohica +1.6 \| April 24, 2009 at 2:50 PM 0
So could I use this to boost the 3.3V digital out from an Arduino mini pro to 5V and then drive the TTL in on the SN754410 h-bridge?

	by Matthew +4.3 \| May 4, 2009 at 0:38 AM –0.22
Works great, But Really small and easy to lose! (But that's just me)

	by AretCarlsen +5.9 \| June 5, 2009 at 9:52 AM 0
The description is inaccurate. It reads, "A digital one going into the RXI pin on the 5V side will show up on the RXO pin on the 3.3V side as 3.3V." In fact, a digital one going into the RXI pin on the 5V side will show up on the RXO pin on the 3.3V side as 2.5V.

	by SeanReynoldsCS +2.8 \| December 1, 2009 at 6:50 AM 0
I'd really like to use this to Power a 3.3v circuit. I'm guessing it will do that just fine, but is there some kinda current limit on this I should be aware of? Everything on the page talks about communications but I really just care about power. Would this work for that too?

	by Reed +1.8 \| December 14, 2009 at 6:17 PM 0
This board has no provisions to provide any sort of power to a circuit. It is designated for communications purposes and in order to even do that it requires voltages to already be present in order to function. The parts on-board are mosfets not Voltage-regulators.

	by FlyByPC +2.3 \| January 5, 2010 at 8:19 PM 0
This board is a great example of why SparkFun just "gets it." You just know they've come across this problem themselves, got frustrated with having to solve it multiple times, and came up with a solution. Rock on, guys!

RGFTech

| January 14, 2010 at 1:24 PM

There seems to be enough question around the subject, since the tool is used mostly for I2C and UART, how about a simple couple of schematics showing the I2C connection where the bi-directional lines must be used along with another showing a connection between two UARTS (on microprocessors) and finally between a 3.3v microcontroller and teh RS232 interface to a PC/USB?

Can I assume that the board has to be viewed from the perspective of the low voltage side of the interface you are trying to make? So the TXI will hit the 3.3v TX pin while the TXO will hit the RX pin on the 5v device? Sorry for not being bright enough to figure that out on my own.

ehubin

+1.2

| January 20, 2010 at 6:42 AM

I bought two of these to convert levels between a 5v Arduino (arduimu) and a PNI micromag 3.

I did initially used the ports as suggested in the images above and it didn't work.
After some investigation, it turned out the level of signals from Arduino(5V) toward the micromag 93.3V) where at 2.5 instead of 3.3V.
I managed to get it to work by hijacking one of the TXO connections on Arduino side to convey the Reset signal. Other SPI signals (MOSI,SCK) where fine at 2.5V.

@Sparkfun, Would be good to highlight this in the Product info as already suggested above. If ever you build a new series of converter, might be good to tune the Voltage divider to effectively output 3.3v when supplied with 5V on the High side.