SparkFun Forums

[Unterhausen]

We would like to use the LED backpack http://www.sparkfun.com/commerce/produc ... cts_id=760 to display the internal control state of our robot. We have two choices: interface to an Acroname Brainstem or to a pc over usb or rs232. It looks like the Brainstem is out, because it's not easy to get spi working, and the AVR on the backpack uses one of the I2C lines to drive the LED's. So is there an easy way of hooking the backpack to a PC? In the link I gave above, it looks like it's hooked up to the PC using JTAG. Since I have a ton of usb to logic level rs232 converters, that is the approach I prefer. Otherwise, I'm thinking of getting an arduino board for this purpose, but I haven't checked out how hard it is to use the SPI.

I'm probably making this too difficult. Any ideas?

[roach]

If you're not married to the Brainstem, you could try interfacing the backpack to an intermediary uC, like an AtTiny or PIC, via SPI, then pass commands to the uC over TTL serial, using your USB -> rs232 converters. Would probably involve writing about ten lines of firmware to handle the commands. You could send commands from any standard terminal program on the PC.

[Unterhausen]

I would like to avoid complexity if at all possible, and if I could limit the circuitry to the led backpack, that would be ideal. The more processors involved, the larger the chance for failure. I'm not married to the Brainstem, but the grad students that work with me are, and they are really good at pretending they are stupid and saying "this thing you made us use doesn't work."

I'm going to look into the usb bitwacker to see if I can use that. http://www.sparkfun.com/commerce/produc ... cts_id=762

Although, it might be better to have something I can permanently program to pass through the data.

[Unterhausen]

looks like the bitwacker would work. It appears that the SPI pins are sent out to the header connections.

The brainstem uses an 18c252. I stared at the 18c252 data sheet for a while, and it appears that I2C and SPI are mutually exclusive, so the Brainstem option is out.