View Full Version : Compatibility Check

01-21-2009, 04:47 AM
Hey guys,

Can I connect this device to the propellers I2C pins (29 and 28) without ill affects?


Its the ds1307 real time clock.

Or should I put resistors between it and the I2C line?



01-21-2009, 05:02 AM
The DS1307 works fine at 3.3V go ahead use it at the lower voltage. How is your Propeller set up? on a breadboard or circuit board? You'll want pullup resistors on the I2c lines, I assume that you already have if you have an EEPROM connected. (some boards only pull up SDA, some both)

If you want to run the DS1307 at 5 V simply put a 1k resistor inline between the DS1307 and the rest of the I2C bus.


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01-21-2009, 05:23 AM
Thanks, I'll just run it at 5v with 1k resistors inline.

I'm using the prop proto board btw.


Carl Hayes
01-21-2009, 11:12 AM
Should work fine with pullup resistors. Caution, though -- when you want to pull a line low, set the pin LOW and OUTPUT. When you want it high, set it INPUT and let the resistors pull it high, lest the Prop try to pull it high and another device try to pull it low at the same time, POOF, another 12 bucks down the tube. That's an invariable necessity with I2C.

-- Carl, nn5i@arrl.net (mailto:nn5i@arrl.net)