I2C connections

[100317]

Hello,

I have some questions concerning I2C connection.

Normally, each I2c device has his own Address and additional the Address lines A0 - A3.
Each manufacturer has his unique Address for each device.

How many I2C devices are possible?
Are there electrical limitations?
Has someone already done this?
Are there practical experiences?

Thanks,

Greetings,
Hans

 

[papaof2]

You can search the forum for i2c, but you must enter the search term as
i2c*
to bypass the requirement for a search term to be greater than 3 characters.

John

 

[hippy]

Every I2C has a 7-bit, 8-bit or 10-bit device address and usually a 3-leg address selector(A0-A2). It is therefore possible to connect eight of the same devices to a single I2C bus, more with additional hardware which can select a specific I2C device. Or use multiple I2C buses from a single PICAXE ( requires writing ones own software ).

Note that some I2C devices may not use all A0-A2 legs even if present.

Theoretically the I2C bus could support an infinite number of devices so long as only one were selected at a time, but the nature of the open-collector bus means full-speed operation deteriorate as each device adds some capacitance to that line.

One can slow the bus down and use more devices that way ( and the same helps for devices a distance away from the PICAXE ) but there probably is some point where the bus becomes too slow or unreliable for practical use. In most cases though you should be able to use as many I2C devices as you need.

 

[100317]

Thanks

Hi,
thanks for the quick reply.

I will try it in my next Project.

@Hippy,

i visit your home page and i used your instructions for implementation of a LCD in a Picaxe Project.
I just copied your demoprogram into the editor and download it into the Picaxe.
I am happy to say: IT WORKS.

One problem i have with the contrast. I put a 10K Pot into my project and when i turn it to GND, the Characters at the display are very weak.

Many Thanks and best regards.

Hans

 

[hippy]

Most LCD's I've used will give reasonable contrast when connected to 0V. Check it's not one of those displays which has better contrast when looking down from the top - that is, if held parallel in front of you, does it look better when your arms are below your head than when above.

Some displays may want a negative contrast voltage but don't apply that unless you've checked the datasheet first or you could well destroy the LCD. Also check what the supply voltage to the LCD is.

 

[100317]

Dont have a Datasheet for this device. The seller mentioned only that the LCD has an HD44780 controller.
So i made the wiring and try out. First i put the pot between V+ and GND the middle to contrast. Later i disconnected the V+, with the same result.
The LCD has a backlight. I put an additional 10K pot into my project, now i can adjust the contrast and the backlight.
This may be the reason, as the price for the LCD was only 6,9 euro.