Ds-1302

MikeS

I am wanting to add some short-term back up to a DS-1302 time keeping chip. Documentation refers to a "super cap". Is this a large value electrolytic or a special memory backup capacitor? Also I am not sure if I understand how to configure the trickle charge circuit with the diode and resistor. Is it between the two Vcc pins or between one of the pins and ground?

thanks

Newzed

Why not just add a backup battery.· They are inexpensive and last about 7 years.

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Sid Weaver
New Combo LCD Backpack

http://hometown.aol.com/newzed/index.html
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allanlane5

A 'Super-Cap' is a high-internal Resistance, high-capacity (1 or 2 Farad) capacitor. It's not your normal capacitor. Its purpose in life is to provide battery-backup for RTC (real-time clock) chips like the DS1302. I believe a 'fully charged' super-cap will run the chip for a week. You *must* buy a 'Super-Cap' if you want to do this. 'Normal' capacitors are entirely un-suitable.

On the other hand, a CR2032 3 volt coin cell will run the RTC for over a year -- and will last for 5 years, if the power never goes off. Something to think about.

Chris Savage

I agree with Sid and Allan...I have 2 projects that have been running a DS1302 using a Battery as a backup...Keeps the code and the circuit simpler.· Besides, it only uses the backup when the main power fails.



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Chris Savage

Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777

Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
Designs Page:··· http://www.lightlink.com/dream/designs
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MikeS

After thinking about it ....you guys are right. I'll go with the battery.

Thanks for your responce.

lrohn

If a CR2032 is used as a battery backup, would you connect it to VCC1 and disable the trickle charger circuitry?