Can anyone suggest a good battery for a rtc? I have an mcp79410 which works down to 1.3v, I had bought an rtc battery off ebay but it only seems to last an hour or two before it stops running
You mean a battery to connect to the Vbat pin? Lithium coin cells such as CR2032 are widely used for this purpose.
I'm not sure what a "rtc battery" is.
That’s an interesting RTC. Quickly looking at the datasheet I see: Battery Backup Current: <700nA @ 1.8V. Any 3V coin cell ought to last years at that rate. Is everything wired as recommended by the datasheet? Either something is hooked up wrong or they’re selling dead batteries on eBay again XD
Maybe thats the case, it was a cheap battery, but it'll hold memory for some time but ill check it later and its stopped I have it wired according to the specs, idk why its not lasting I guess ill try it wil 2 AAs and see if its the battery or some weird phenom
The backup battery should be connected to the VBAT pin only. It should not be connected to the VCC pin or powering anything else. Just about any common 3V Lithium coin cell should work, 20xx, 16xx, or 12xx. I use CR1220s which are the smallest.
You might try measuring the current when on battery.
Did you try to connect the battery to an Analog In on the Arduino? That'll cause excessive current draw.
The only wiring in common is the ground, the + only goes to vbat can things other than low battery influence it? Im noticing sometimes the osc will keep running more than two hours but the month register will be off track somehow
Could the RTC chip be defective? Did you replace it with another one? Same results?
I don't know, I bought one just because I saw it cheap on ebay, I don't have another but could handling it affect it at all? Like static?
winner10920: I don't know, I bought one just because I saw it cheap on ebay, I don't have another but could handling it affect it at all? Like static?
Yes eBay. Known for their reputable sellers. I highly doubt this was a knock-off chip, a reject from the original factory, or something that was relabeled. (Note that by "doubt", I actually mean "expect.")
eBay can be a good source for passive components, but I wouldn't trust anything active. In fact, I'd double check the value of anything passive I bought as well.
That’s probably it, its acting fishy because the last 10 hrs its been fine, unlike before
I can’t seem to find what’s causing it to stop/error, probably not the battery
Decoupling? Crystal not mounted over ground-plane? High currents flowing near the crystal? The RTC chips run the crystal at extremely low powers and this part of the circuitry must be protected from electronic noise (basically close to a ground plane and not near any source of inductive pick up).
I have the caps, ground im gonna let it sit perfectly still for a while , maybe run an accuracy test and see if maybe its just my computers emf messing with it