anthrolume

As such, you'd need a pull-up resistor on Points A AND B in your schematic - and also between the two ULN2004 inverters
- Point B to pull up the base of the ULN2004 transistor (can probably be about 2.2KOhm)
- Point A - the regular pull-up for the I2C bus since the ULN2004 is not a push-pull output (approx 2.2k or less)
- BETWEEN then 2 inverters of the ULN2004, to pull up the base of the second inverter (I would try a 2.2KOhm resistor here)

Awesome! Thanks a ton Mike. I'll try that this weekend.

-Bryan

I just bought my first breadboard ever. Some resistors and LEDs as well

LCD lives thanx to you. I use 4k7 resistors and wiring like anthrolume recommended.

Great news! Way to go pavgud!

-Bryan
(anthrolume)

I got a couple ULN2004As and I'm trying to put together an I2C bus driver using that part. I only have the vaguest idea what I'm doing.

Here's my current schematic:



This is just the schematic for SCL - I'm doing the same thing to the data line too.

Since the ULN2004A elemnts are inverters, I've put two in serial to get the same signal out as I put in.

Pin 8 is grounded. Pin 9 is tied to +5V.

My questions:
1) Am I powering this chip correctly?
2) I think I still need to pull up the I2C bus. But where? At point A on the schematic? Or at point B?
3) Pulling up at point B, I seem to get a reasonable signal at the other side of the first inverter, but not after the second. Why is that?

Thanks in advance for any advice.

-Bryan

Had a read of the thread. Not sure if this is the answer but maybe it is.

You can get I2C buffer ic's like the on in this link, only £2 or £3 for the IC. Farnell stock them.

http://www.nxp.com/d...heet/P82B96.pdf

It might be the low drive from the netduino thats the problem.

Thanks Darren! Those seem to have Tx and Rx outs, rather than just being straight up drivers, so I'm not sure that's what I'm looking for, but I'll go look at the application notes for that part. Thanks a ton for the pointer.

-Bryan

Well nothing I've tried seems to be helping, and my meager knowledge of fundamental electronics is failing me. The biggest difference I can find between the Arduino (which works perfectly with 50 I2C devices on my buss) and the Netduino (which works with up to about 35 I2C devices on the same physical buss, but fails after that), is that an Arduino can deliver 40mA to its I2C port, and the Netduino can only do 8mA. I don't know if that's salient, but that's the biggest magnitude difference I can find.

So I ordered a couple UN2004As. I'm going to try to rig up those as external drivers and see how it goes.

I really hope I can get this to work, otherwise I'll have to abandon the Netduino for this project, and I really much prefer it.

-Bryan