DS1307 RTC problem?

[radiok0tw]

I'm probably doing something wrong. Any help would be appreciated.

My project reads the date & time from a DS1307 RTC module and transmits that info (and some other data), via an RF24 transmit/receive link, to a 2nd Arduino where the data is displayed on the serial port of that 2nd device. I have the transmitting Arduino connected to both the USB cable and to an external 5V power supply. As long as the USB cable is connected on both ends everything works great. The 2nd Arduino receives the date & time over RF and displays it via it's serial port just fine.

But if I then disconnect the USB cable while everything is working OK, from the transmitting Arduino, leaving it powered by the 5V external power supply, the 2nd Arduino receives and displays bad date & time data. What happens with the DS1307 when I unplug the USB cable? I would have expected it to continue supplying correct date & time data with the USB cable disconnected since that Arduino still has power and all other functions are working OK.

Both Arduinos are Mega2560s and the DS1307 has a new battery.

Thanks.
Tom

[anon57585045]

How much current and voltage does the RF24 require? Why do you think the RTC is the problem, specifically?

Does your "other data" arrive intact?

Please post a wiring diagram of the sending system.

[pylon]

@radiok0tw

What happens with the DS1307 when I unplug the USB cable?

Most probably the system voltage falls below about 4.6V (1.25 x battery voltage) and the DS1307 deactivates the I2C interface.
As you didn't tell us where you put the 5V power to or which exact power supply you used, we expected that information from the wiring diagram. Oh, wait, you forgot that information too.