Small logic level converter for SPI?

Using Arduino General Electronics
#1

I am working on a small board (1x2 inches or smaller if possible.) which will have a microSD socket on it. I'm looking at level converters and most seem to be hex or octal versions on 14 pin devices.

I only need 3 for SPI, I believe... MOSI, SCK and CS.

Is there anything out there physically smaller that can still be hand soldered? What about "Hack-around" versions using diodes or resistors that may take up less real estate or allow me to divide the space up around the board more effectively? (I do need to keep full speed I think... I be streaming files to SimpleSDAudio)

Any advice or guidance or links to info sources appreciated!

Troy

#2

How about TXB0104?

Will anything else be on the MISO line? Like a 5V part? Will need that buffered going back to the uC also if there is.

#3

If it's only data signals then you probably don't need much.

Going from 5V to 3.3V? Two resistors to divide the voltage.

Going from 3.3V to an Arduino pin? There's no need for anything. Arduinos recognize 3.3V as HIGH.

Going from 3.3V to some other device? You'd better tell us what the device is.

#4

TroyO,

I picked up a hand solderable "Level Converter" from SparkFun a while back. They're pretty small and may work for your application.

There are 6 pins on each side 5v/3.3v.

Pat.

#5

Adafruit sells several different level-shifter chips.

#6

Ideally you would have something like this. The uSD card is buffered from any 5v signals on the SPI bus.

microSD_buffer.jpg
microSD_buffer.jpg960×720 40.4 KB

#7

Thanks all. That one will work, I guess it just bugs me to have "extra pins" not being used, LOL.

I guess I could always just buffer MISO just to make me feel better, LOL. :stuck_out_tongue:

#8

Extra pins on what? The TXB0104?
You could use 2 TXB0102

or 4 TXB0101

but then you're duplicating Vcca, Vccb, OE/, Gnd numerous times and you need a capacitor for each part.

#9

I just mean that there are 2 NC pins, and 2 pins that I wouldn't "need" to accomplish the level shifting required so ther are 4 "extra pins" not relevant to what I want to do.

I actually found something like what I want in this one:

SN74LVC3G34DCTR

Is it a big difference? Nope, LOL... we are grasping straws here for sure.

Unrelated question though, is there a TI to "Rest of the world" translation for package designation? "DCT (R-PDSO-G8)" seems to be a PSOP8?

Thank you very much for the help, that TXB0104 may be the winner anyway for availability reasons.

#10

Please explain which 2 you don't think you "need". My opinion is that you Need them as shown unless you will have no other SPI activity ongoing, so nothing will take the MISO line high to damage your SD card.

The 74lvc3g34, you're gonna power that from 3.3V, and drive the inputs with 5V? And then rely on the part to clamp the input voltage down to 3.3V. The arduino will try and drive all the current it can to bring the output higher, which the 3g34 will clamp up to 50mA worth - better plan on series current limit resistors in accordance with Note 2 on page 2 of the datasheet to avoid long term damage to either part:

(2) The input negative-voltage and output voltage ratings may be exceeded if the input and output clamp-current ratings are observed.

#11

No other SPI devices, correct.

Power available is either 5v or 3.3v.

I am working on an "Arduino Nano lightsaber shield" project.

In the end I need to get:
microSD socket and buffers,
accelerometer
audio amp (1-2 watt)
LED driver (Output up to 2A, PWM dimmable)

All on to a 1" x 2" circuit board that connects to an Arduino Nano..... by far my most ambitious effort so far.

On one hand I have a known winner (TXB0104) and it does fit the space requirements and being "hand solder-able" a lot better than the 14 pin DIP I started out looking at, so maybe I need to just stop over analyzing.

I'm new at this stuff and sometimes I understand just enough theory to get myself drowned. :wink:

Thanks, it may have taken a 2x4 to get me to listen but I eventually do, LOL.

#12

I guess I could always just buffer MISO just to make me feel better, LOL.

Actually, MISO is the one line you probably don't need to buffer, whereas SCK,MOSI,SS
all need buffering when going from 5V Arduino to 3.3V parts.

#13

But it is still good practice to buffer it anyway, who knows, you may need to reprogram the bootloader, or decide to upload a sketch without the bootloader, and then you’ll have 5V on MISO.

#14

Good point.... the hope is to make something open platform available for lightsaber builders. (Yes, there are folks who spend way too much time and money on this, LOL.)

To that end.... bulletproofing the design where possible is a good idea. Plus, as noted.... the TXB is absolutely adequate for the need, buffers all the lines and fits the size and solderability requirement... winner!

#15