Help with DS1302 RTC Module

Hi everybody, I was working with the RTC DS1302 module fine, until I connected the RTC to a 9V battery.

I will explain the connection, 9v Battery 250mA --> IC7805 --> 16v 100up capacitor --> RTC DS1302

I know that the clock is working but the RTC does not syncronize. Any ideas... ?

Best regards, Ginza.

I know that the clock is working but the RTC does not syncronize

Please provide some more detail as to the exact nature of the problem. What is working? What is not working? How do you know?

Hi cattledog, look, I have working with this module since one month to now and never failed. I have configured the time by serial and bluetooth, and both ways were working properly.

But this strange behavior starts today, after I want put the RTC module with its own power supply (9v battery).

Im thinking that perhaps the RTC crystal was damaged. I was reading the datasheet 20min ago, and it says that the RTC module doesnt need external resistors or capacitors.

I have used the 100up capacitor to stabilize the 5v voltage of the 7805 IC.

But this strange behavior starts today,

What strange behavior? Can you not set the time on the rtc? Can you not read the time from the rtc? Is the time not updating in the rtc registers?

Please try and provide a more complete problem statement.

Can you go back to the way you were supplying the module before you tried the battery and voltage regulator? What is the behavior under the original conditions where it was previously working? What was previously connected to Vcc1 and Vcc2.

The 7805 is not specified for less than 5ma. but it looks like the ds1302 draws less than 1.5ma at 5v. Did you measure the unloaded output with a meter? It may be exceeding 5v, and the ds1302 is typ 3.3v and max 5.5.

I have measured with the tester and after the 7805, first the tester says 1.5A and after some minutes it says 0.25A.

The 9v that im using has 250mA.

I noticed that the battery is rising temperature, is normal ?

I have measured with the tester the Arduino UNO 5v output and it has 1.5A, I have used always the RTC connected with the Arduino 5v output and always works fine.

I have tested the RTC module now with my code and it works properly again connected to the Arduino 5v output.

Im using a cheap tester, perhaps it is failing with the masures.

What do you recommend me to conect the RTC module, directly to 7805 or to the Arduino 5v output ?

Best regards, Ginza.

If the ds1302 module has its own coin cell back up battery, I do not see why you would want to change its primary power supply from the Vcc provided by the Arduino.

Yes cattledog, Im using the coin battery into the RTC.

I think that was the same the 5v from the 7805IC that the 5v from the Arduino. I have measured with the tester and it says the same in voltage and intensity. The tester that im using is very cheap, perhaps it is wrong.

Do you say that I must connect the RTC directly to the 5v from the Arduino to work properly ?

Sorry for my english... :slight_smile: Im spanish.

Do you say that I must connect the RTC directly to the 5v from the Arduino to work properly ?

It’s not clear what each of us mean when referring to the RTC. Is it the chip or a module?

You said that you were using a ds1302 module (and not the bare chip and crystal oscillator on a breadboard). If so, I think there should be a one pin for the power. The back up battery should be connected internally on the module. If I am not correct, please provide information on the module, or a schematic of the chip and how you have it hooked up if you are not using a module.

Is not only the chip, I have the PCB with DS1302 IC socket, DS1302 IC, coin battery and crystal. It has 5 pinouts. 3 for data and the other 2 for Gnd and Vcc.

Im trying to leave the arduino board and get the project to a protoboard, so I thinked to connect the power supply to the RTC module at the same line that the ATMega328.

I think im wrong, I should connect the RTC to the ATMega328 Vcc, no?

Please draw a schematic of what you are trying to do.

Ok, I will do.

Best regards, Ginza.