I’ve set up a microbit with an Elecfreak Octopus RTC board a while ago. This board has an optional battery holder to keep the DS1307 running if the board is disconnected.
Today I’ve noticed that the display shows the time as 00:00. After checking the code and the battery I found that if I remove the battery the display shows 22:22 and I could change hours and minutes using my MakeCode program. But as soon I as I put the battery in again the time shows 00:00.
Checking the battery shows 3.2 Volts.
This is very strange since I have two other boards with the same chip (DS1307) and they have a backup battery inserted as well and they are working as expected.
Any help is welcome.
solved: after I was surprised that the RTC shows a zero time when the 3V lithium cell is used, I tried everything that could be related to the backup battery or have an effect on the RTC module. The answer can be found in the data sheet of the Dallas IC DS1307. If the input voltage (Vss) is less than 1.25 * VBat, i.e. 3.2V of the lithium cell, then the R/W operations are blocked.
The RTC board is connected to Octopus board from Elecfreaks and this board can be switched between 5V and 3.3V for different connected modules. From previous experiments it was still switched to 3.3V. The RTC module from Elecfreaks must be operated with 5V. Now my clock is running again and retains its values when the experiment is switched off.
1 Like