rsdio tipped us to an app note on interface circuits:
hmm… breakout board candidate?
This circuit provides a direct I²C interface to your PC’s USB port. A USB to 1-Wire® dongle supplies the PC with a 1-Wire master, which controls a 1-Wire I/O extender. This I/O extender has two bidirectional open drain ports, which the PC can write to and read from. By generating the right logic signals on these two ports, the PC can emulate an I²C master.
Thanks rsdio!
Wow.This is spiffy. The last time I had to jump through hoops to interface a i2c slave to an USB master using them psoc chips. Expensive and closed source. I can see myself using one of these puppies with the elcheapo pic18k series USB devices. I would love a breakout board. Thanks Ian and Rsdio. Good find.
What is the obsession with Maxim parts on this board? There have to be at least three one chip USB/I2C solutions out there. If memory serves some can enumerate as high current devices so you can feed your power hungry dongles with up to 500mA (if your USB port can supply it) and not be stuck at 100mA max.
“What is the obsession with Maxim parts on this board?”
Get ’em here because you won’t be able to find them anywhere else ;) (joke about Maxim part availability)
There seem to be mixed feeling about the app note posts :) Maybe we should do a roundup instead.
Some of these are up so you can say ‘wow, what an obtuse design’ and have fun mocking the guy who came up with it.
The availability is indeed a problem. The DS9490 still seems to be available but the DS2490 chip, which the DS9490 is based on, is definitely discontinued and there isn’t any equivalent substitute available from Maxim.
I’m fine with Maxim parts and the unusual design. What makes me go ewww is the massive overhead from 1-Wire which thankfully is slightly less due to only having 1 slave on the bus. They even mention it in the app note “Because the software overhead is large, the rate at which this circuit generates signals is limited to approximately 20bps.” <— Blazing fast! ;)
Still, it is an interesting idea and shows what you can do if you have reasonably generic building blocks and how quickly you can make something.
I'd suggest something else like a PIC directly interfaced to USB which does hardware or software I2C instead of relying on another chip like this design. So yeah, go buy a Bus Pirate v4 instead ;)
I dont think that there is a obsession with Maxim any more than Microchip, Analog Devices, Texas Instruments. I worked for TI for 25+ years and like their stuff but I am open to anyone’s cool products other than SF (just jokeing).
BTW here is another USB to I2C converter using Atmel and NXP. http://linkm.googlecode.com/svn/trunk/docs/LinkM_datasheet.pdf
USB/I2C-Converter using only 1 ATmega8. It’s open source.
http://www.robotfuzz.com/OSIF_guide
I’ve built it, it works fine.
Regards,
Jan
I post Maxim parts because they do a good job of making their parts known. Too bad they can’t make them available! But the point is to be aware of what is out there.
If anyone knows of several other chips which perform the same functions, then write ’em up! I’d like to hear about these parts. Just make sure they haven’t already been covered.
As for this solution versus PIC: I love writing PIC firmware, because it’s easy for me. But not everybody wants to write firmware and figure out how to load it onto their board. Sometimes it’s easier to just hard-wire something that can be controlled by host software. Personally, I agree with the suggestion to build something like this on top of the PIC, but such project seem to take longer to launch.