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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Eddd on October 22, 2014, 03:33:47 am

Title: Problem with DS1307 RTC
Post by: Eddd on October 22, 2014, 03:33:47 am

I have strange problem with DS1307 Real Time Clock. It is custom made PCB which contains Atmel ATmega 2560. When I run I2C scan test program to list all the devices on the I2C, I can't find DS1307 (which it should be at address 0x68), but other I2C devices are listed and work fine. But once I connect the battery, the whole I2C bus go down and nothing is listed. The schematics is shown below in the attached picture.

What do think the problem is?

Title: Re: Problem with DS1307 RTC
Post by: diegoterc3 on October 22, 2014, 04:41:40 am

I assume you know you need pull-up resistors. Depending on the number of devices you will need to calculate the resistance value. Here is a link that can help.

http://www.edn.com/design/analog/4371297/Design-calculations-for-robust-I2C-communications (http://www.edn.com/design/analog/4371297/Design-calculations-for-robust-I2C-communications)

Had the same problem a while ago. Hope it helps.

Title: Re: Problem with DS1307 RTC
Post by: SL4P on October 22, 2014, 04:54:33 am

That would be my bet - as well s ensuring all ground refs are tied to the same 0V point.
Programmer/external supply ground could be isolated from the 'real' uC 0V - so everything floats when not connected.