Skywriter I2C Address(es)


#1

Hi, I was reluctant to categorize this under support since I haven’t yet made a purchase of any Skywriters however it seemed like the best place for this post.

I have been wondering if it is possible to change the I2C address of a Skywriter (hat or otherwise) in order to connect two Skywriters to one Raspberry Pi or Arduino. I want two handed control…


#2

no, it’s not possible to change the address I believe, but it might be possible to use the second i2c bus on the Pi (or Arduino, depending on the board).

Transfer/Reset pins are specified in the library and presumably you could somehow control multiple units with some level of hacking (or making your own).

That said, I better light up the Wiz sign into the sky and summon @gadgetoid to shed some light on the dark corners of this endeavour.


#3

Thank you for your prompt reply.

I was surprised by your answer because my preliminary research seemed to indicate that it might be possible.

I found datasheets for the MGC3130 chip that runs the Skywriter.

One datasheet says the following:

One pin (IS2) is available for address selection and
enables the user to connect up to two MGC3130 devices on the same bus without
address conflict.(page 13)

The other datasheet indicates that IS2 should be set to 1 in order to change the I2C address of the chip from 0x42 to 0x43.(page 22)

However I have no idea how to do this. Would that mean connecting the pin to 3.3 or 5 volts or to ground?

Any insight would be appreciated.

Did that Bat Signal work?


#4

I don’t have access to the schematics but I would presume the chip IS2 pin is bound to the ground plane.

I doubt it would be possible to toggle it to make the address selectable, but since I hardly consider myself an authority on the matter, let’s light the Wiz sign in the sky once more and see what happens ;-)

@gadgetoid


#5

ZActually, I have just tried and there is a simple way to switch the I2C address… theré’s a 10k pull-down resistor attached to IS2 that can be snipped away /desoldered and will return the pin high.

Here’s a pic of two Skywriters using different addresses: on the left, factory 0x42; on the right modified for 0x43

EDIT: on the other hand I suspect this would leave the pin in a floating state, so not sure about stable operation for long period, it probably needs a pull-up fitted to ensure the address stays at 0x43