Connecting a battery for the RTC

The EC1 includes a true Real Time Clock and calendar function. This EasyStep will show you how to connect a battery to your EC1 "EasyOne" so the clock can keep the time when the board is not under power

What you will need

• Holder for two AA or AAA batteries with 2-pin female connector. Example
• Two AA batteries, 1.5V each

Alternatively you could use a single 3V button cell in a suitable holder. The AA batteries are readily available, cheap, and will last a very long time.

Wiring

The picture below shows the wiring. The EC1 battery pins are the two pins at the corner closest to the push button. They are marked 0V and V_bat. Make sure you connect the red (positive) lead to V_bat.

CAUTION: Do not use a battery over 3.3V.

Testing

Once you have a program that can display the time, you should test the battery. Here's a plan:

• Set the time and make sure it is reading out correctly;
• Power down the board;
• Leave it without power for several minutes (make a note of how long). Capacitors on the board can supply the RTC for quite some time;
• Power it up again and check that the time is still correct;
• Repeat the test without the battery connected and verify that it fails with the same amount of time without power (or preferably less time).

We estimate that the onboard capacitor can supply the RTC for up to 5 seconds, but during testing for this EasyStep the test unit went for about 30 seconds without losing the time.