| Electronics > Projects, Designs, and Technical Stuff |
| RTC source voltage |
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| Chris3D:
First, Happy Holidays to all! I'm making a small wrist watch for my son using an ATTiny841 and keeping time with an M41T62 RTC from ST, all powered by a single lipo cell. I'm trying to keep the component count as low as possible, and I'm wondering if the accuracy of the RTC will be affected if I power it directly from the battery vs. through a small voltage regulator. Powered from the battery, the voltage to the RTC will vary between 4.2v fully charged to ~3 volts. This is within the source voltage range of the RTC (1.3 to 4.4v). I just don't know if this will effect the RTCs accuracy vs. powering it through, say, a small 3.3v regulator so it always sees a steady voltage. If I could save the space on the PCB of the regulator and caps, that would be great, but if it's going to throw off the accuracy, I'll fit them in. Thanks in advance! -Chris |
| ataradov:
No, it should not matter at all. |
| Dave:
The voltage doesn't matter much. What does matter is correct capacitive loading of the crystal. Make sure you read your crystal's and microcontroller's datasheets and use the correct value capacitors (preferably C0G ceramic type). It is also desirable to isolate the ground currents of the oscillator from the rest of the circuit, but that's just a minor difference. |
| Chris3D:
Thanks for the replies guys! I'm using the LCC8 package version of the RTC, which has an integrated crystal and related components, so I didn't have to worry about precisely matching those. That and because it's tiny! Here are boards I made for the RTC (right) and a 28 channel LED driver (left) I'll be using. I'm new at all this and just figuring it out as I go, so I make up small boards to test out new circuits and/or ICs before building them into something larger. So it'd be useful afterwards, I powered the RTC through a 3.3v regulator on the little board, but for the watch, not needing that or the backup supercap will save quite a bit of space. I'm trying to keep the watch as small as possible since my son is 9yo and he'd look funny with a giant circuit board on his wrist... or funnier than he'll already look with a circuit board on his wrist! ;D |
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