Seeeduino + i2c /RTC


RTC module is the sparkfun one.

I have a working i2c/RTC setup with a duemilanove on pin 4 & 5.

I switched to a seeeduino MEGA with i2c on pin 20 & 21 using the exact same code. I am unable to get the RTC clock to work...

anyone had the same problem? Do I need pull up resistor?

I’m using a Seeeduino Mega with a small DS-1307 RTC module and it works fine. The module does have optional pull-up resistors on the I2C clock and data pins and they are enabled.


Can you tell me exactly what module you are using? I am using the Sparkfun one. I guess I am SOL :(

I'm using a ETT module, has no part number. Is this the SparkFun module you are using:

If so, I doesn't look too difficult to solder two 5k ohm resistors, each wired from the data pin and clock pin to +5vdc pin.


Yes that is the module. I am wondering why is there such a change when they claim some sort of compatibility with arduino?

Well I removed the jumpers that enable the pull-up resistor and my module still works without them. However I do believe the I2C specifics using pull-ups. Are you sure of the code you are using?


I will double check the code but the only thing that changed is the hardware according to my svn tree...

I've used I2C on my Seeeduino mega without pull-ups, I've got 5 external eeprom hooked up.

I believe the Wire library always uses the internal pull-ups, and as far as I'm aware, there is no way to disable them in a sketch? (I said as far as I'm aware! I don't think there are any commands to disable it)

Make sure you've got the right data lines connected. When switching from my Duemilanove to my Seeeduino mega, I often get em mixed up!

right line is with the seeeduino MEGA: i2c on pin 20 & 21 right?

Yup but they're switched around, as far as positioning goes.

On the Seeeduino mega, SCL is on the left, and SDA is on the right.. for Duemilanove's, SCL is on the right side, while SDA is on the left. (in terms of position of pins, not on the board.)

Try flip them around, move the pin from 21 to 20 and vice versa.

Does that do you any good?

I will try but I am pretty sure they are hooked up correctly :(

ok so code hasnt changed and hardware is correctly connected. I decided to set the time again and everything worked now. I am wondering if the board change made some sort of reset of the RTC sparkfun board. Like shorting SDA and SCL while changing the board in the setup. I will test that out tonight.

but now, I have another issue. I am feeding the seeeduino with a 12V and it shutdown after 2 minutes.... like from overheating or something :/ my duemilanove works flawlessly.

12V is too high. It probably is getting too hot, and shutting down.

according to the spec:

12V is not too high according to the spec.

this an automotive application so I might be pushing 14V when the car is running damm it :( I have to check that...

Is there a way to read the voltage applied to Vin via software?

Is there a way to read the voltage applied to Vin via software?

Yes, but only if you wire the Vin pin to a voltage divider resistor string so that the maximum voltage possible is =<5vdc, wire the reduced voltage to a analog input pin and then scale it back up in software.


good idea. thanx a lot!