Best way to logic shift?

Other Hardware General Electronics
1

I am desiging a custom PCB with a Mega 2560 and would like to embed my xbee/wifi and need to figure out the best way to shift the logic.

I found these

http://www.sparkfun.com/products/8745 Seems inefficient?

XBee Adapter kit [v1.1] : ID 126 : $10.00 : Adafruit Industries, Unique & fun DIY electronics and kits ? Any one know which chip this is?

What is the best way to do this? With least power loss?

Thanks!

2

I don't know about best but chips like the TXB0104/6/8 should be petty easy to use. The work both ways.

Rob

3

I was thinking I could but the Adafruit one and just use the parts on my board.

It would have to be 8bit right?

Any of these?

http://www.mouser.com/Semiconductors/Logic-ICs/Translation-Voltage-Levels/_/N-4s6ih?Keyword=TXB0108&FS=True

4

Normally you only use Rx and Tx so unless you use more pins (possible) the TXB0104 should do.

However that adafruit board has everything you need, regulator, level converters and everything and it's only $10, I'd just get that unless you plan to go into production.

Rob

5

So the transistor looking think is the Regulator?

Hmm then I could copy the traces to my design? Too bad its not like Sparkfun with the eagle files.

Or I could make a header and mate this board

I guess I can do the same with the Adafruit board and just have header pins stick out and solder it on top of mine.

6

For 10 bucks I'd just put a horizontal socket strip on the board and plug the Adafruit board into that. BUT, if you want the job to look more "native" to your design then add 2 10-way 2mm socket strips and a TXB chip.

It probably depends on if this is a product or a one-off for private use.

Rob

7

Well for now its just for home use, but you never know....

Yeah I might go the adafruit route, my head is going to explode already with just the other stuff. Then I don't have to figure out the ins and outs of the the IC.

8

Since the adafruit has a regulator, would that waste power?

I will have a switched 3.3v power source, its just the TX/RX that need shifting, well actually only the Xbee RX does right?

9

That's true, but do you care? Like I said is this a one-off or a production run of 1000s. :slight_smile: It make a difference. If it's running off batteies that makes a difference as well.

To down shift all you need is two resistors. To upshift is harder but if the Xbee puts out 3v3 then that should work directly with a 5v Arduino because the logic high threshold of the AVR chip is 3v.

Not exactly production strength but should work.

You can upshift with a transistor and an inverter or two transistors or a comparator or an opamp, there's no end of options but I reckon those TXB chips have to be the simplest way to go. There's a 1-bit version as well (TXB0101), use resistors for the down shift and the TXB0101 for the up.

The Adafruit board is cheap but at $10 it will add maybe $20-30 to a finished product. You could prototype with that then do a final board.

Too many options eh?

Rob

10

Now that I see how the TX works, really easy...

So this part? Just double checking

Then for sure I will be covered.

Thanks so much! Get this part of my project design done.

11

We use those TX's for this very thing, they can shift all the way down to 1.2v which is great if you need to interface 1.8v circuits. We put an octal TX on our xbee adapter, breaking out the extra ports and shifting a few others on the xbee as well, why not use it as a level shift breakout as well:) They work really well and are very easy to use, and pretty darn cheap as well!

12

So this part? Just double checking

Looks right.

Rob