I2c Limitations

Lynxmotion
1

I am considering the Qwerk by Charmed Labs as the brain for the hexapod I am building. I have a number of i2c devices that I would like to employ but the Qwerk only appears to have 4 i2c ports. I’m wondering whether there is a way to increase the number of ports. Given that i2c is a form of bus I’m thinking that I should be able to use something like the Devantech i2c expansion board . Is there anyone around that is familiar with i2c and how one might go about expanding it (assuming it’s possible)?

Thanks,
Dustin

2

The I2C bus uses addresses. Normally you use a different address on each device.

Alan KM6VV

3

Like Alan said, its a bus. You can put all your devices on the the same I2C bus, as long as they have different addresses. You’ll probably only need 1 I2C bus.

Duane

4

I2C allows multiple devices on the same bus provided they have different addresses. There may also be some merit in separating 7 bit from 10 bit address devices onto distinct buses, and low speed from high speed devices onto distinct busses. It really isn’t clear why you would need more than (4) I2C bus channels as this would allow you to meet each of the categories listed.

5

You misunderstand. I’m not talking about distinct bus channels I’m talking about distinct ports (i.e. connectors). I believe, though I’m not sure, that the 4 i2c ports on the Qwerk are actually all on the same bus. What I’m really trying to get at is whether I can increase the number of ports by doing something like connecting one of the ports on the Qwerk to one of the ports on the Devantech i2c expansion board. If this works then given that there 10 ports (4 on the Qwerk and 6 on the i2c expansion) and 2 of them are used (to connect the buses) then I would have a total of 8 available ports. Now that I think about it I guess I could just breadboard the circuit and test it…

Thanks for the replies,
Dustin

6

If you’re talking about passive (no active components) expansion, then maybe you want to refer to them as connectors or “sockets”, rather then PORTS.

Ports usually connotates buffered, or separate addressing for a device.

So yeah, you’d have more sockets. I2C devices often simply have a pair of connectors, thus allowing one to “daisy chain” from one device to another.

Alan KM6VV

7

I agree, bad choice of nomenclature. Though in my defense I was just using the nomenclature defined by the Qwerk manufacturer.

That’s good to know, I was unaware.

Thanks,
Dustin

8

After looking at the Hardware Guide, the answer is yes you can. I’m not sure where your getting the notion that there are 4 I2C connectors on the Qwerk. I only see 2 (page 2 of the PDF.); and there is no mention just how many connectors there are. As for breadboarding your own expansion board, go for for it. Just remember to connect ALL the SAME singals together. There are 4 of them: 5V, GND, SCL, and SDA.

Duane

9

Great! Thanks for the confirmation.

You’re right, there are only 2. Not sure where I got 4 either…

Dustin