Dallas DS1307 Real time clock has stopped working

[jdhar]

rtc oscillator not working

My Dallas DS1307 Real time clock has stopped working for some reason. I can read/write registers using I2C fine, and when I set the time, with the board powered up, the time is changing as I read the registers back. However, when powered off, it stops counting. I have the battery connected properly, and the voltage is abou 3.1V across the Vbat pins. It used to work at first, but for some reason, it has stopped? I have tried re-writing the registers, but that doesn't help either.

Any suggestions?

Added after 22 minutes:

Just thought I would add this - I'm using an oscillator, not a crystal. Does this need to be powered by the battery also, because currently, it is not. Refer to page 1 of the schematics I have posted for my circuit.

 

[Moof]

rtc not working

Your Problem is that you are using an oscilator instead a crystal. So, if you drop the 5volt, your oscillators stops "oscillating" i thinks thats why your your RTC stops counting. And may be your oscillator has diferent parameters (impedance, etc). So my suggest buy a 32.768khz crystal and then is going to work.

 

[pisoiu]

RTC Not working

A crystal is much cheaper than an oscillator. Besides that, you'll have to connect the power supply of the oscillator to the vbatt and the current draw from the battery will be higher than with an crystal. With the current schematics I cannot imagine how this RTC worked without main power supply.
Besides that, the FT232BM is not connected correctly. The AVCC pin must be properly filtered and connected through a resistor to the power supply. That pin powers up a PLL inside the chip, and it must be protected from outside noise. Take a look in the FT232BM datasheet.
/pisoiu

 

[muruga86]

Re: RTC Not working

use a 32.768khz crystal instead of an oscillator. the problem is when u switch of power to the circuit the RTC is gets backup power from baterry and not ur oscillator whose clock only makes the rtc to work and tick time. if u use the crystal the crystal gets power from the same battery powering the rtc and maintains time.

 

[jdhar]

RTC Not working

thx guys, I guess that is the problem - didn't think of that till right after I posted. And pisiou, thx for the feedback.. this is a first revision, and I have made those fixes on the second one. Guess this is another fix required

In general, when is it good to use osc's and when is it good to use xtals?

 

[pisoiu]

RTC Not working

When you don't have to worry about power consumptions, and you need good parameters (stability, good rise/fall times, etc.) it is better to use osc. But in this special case, the oscillator is designed to run with very little power requirements. In this case it is better to use xtal. The oscillators from RTCs are usually designed to be extremely economical (currents in the range of microampers). The amplitude of the oscillation is very low, usually around 0,5V. It is very important to shield the connections with the xtal with a gnd ring, the oscillator is very sensitive to noise. If you want long time precision from that clock, it is better to protect it from that.
/pisoiu