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Topic: ZS-042 DS3231 RTC module (Read 59001 times) previous topic - next topic

mangelozzi

#45
May 06, 2017, 03:48 pm Last Edit: May 06, 2017, 03:55 pm by mangelozzi
Hi Guys,

The battery is supposed to be a back up for when power is removed.
The problem with most of the suggestions above, is then you are only running on the battery the whole time, which will last for less than 8 years.

Ideally you want to run the circuit off the external Vcc if it is present, or run the circuit off the battery if the external voltage goes away.

What we do not want is the battery being charged by Vcc.
We also do not want the battery supplying current to the external circuit when Vcc goes away, because this will discharge it quickly.

All these condition can be met by adding another diode (Dadd) as shown by the attached image.



sterretje

So if that battery is a rechargeable, how will it be charged?

The whole point of the original circuit is to keep a rechargeable battery charged. And if you don't want that to happen, removing the original diode is a lot easier than adding something.

Also, your circuit probably keeps the full circuit powered (in this case the rtc and the eeprom) which will reduce the 'battery life'.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

cjcj

#47
Jun 17, 2017, 04:06 am Last Edit: Jun 17, 2017, 03:22 pm by cjcj
Hi.
I realize this post is a little old, but just a quick question.  In post #2 "dunio" suggested to use a 5.5V 0.47F supercapacitor.

Maybe just adding a supercap in place of the CR2032 is the best long term simplest solution.  I can see these on ebay selling 5PCS for US $1.50.

Is this a good solution and if so, any idea how long the cap would last when the 5V supply to the module is disconnected?

jorgeota

Hello,

After reading the whole post on the matter, I decided to play it safe disabling the charging circuit by removing the 200ohms resistor, but when I put the RTC back on the system, it did not work, the LED its on indicating power but the RTC does not communicate with the arduino.

Everything works correctly replacing the RTC for a non-modified one.

I then soldered the resistor back on and the system works again.

Does anyone have the RTC working without the 200ohms?

Any other ideas?



sterretje

I removed the diode; the effect is the same.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

EKMallon

I've been working with these ZS modules for quite a while, and have compiled an extensive post about them:

https://edwardmallon.wordpress.com/2014/05/21/using-a-cheap-3-ds3231-rtc-at24c32-eeprom-from-ebay/


Near the end of the post you can find photos of boards which combine pin-powering and the diode mod described by mangelozzi.

There are also links to heypete's de-capping & drift testing on these RTC.

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