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Napsal/a: host Publikováno dne: 20.12.2015 16:19:12
To je pěkné, sice ten avr by uměl reálný čas taky, ale asi ne s tak malou spotřebou.
Nevím co je "normální měřič kapacity" ale u hodinkových krystalů hodně bacha na amplitudu kmitů, protože se umí mechanicky poškodit překmitáním, amplituda mechanické výchylky zničí tu křemennou U-ladičku. Jen to tikne a šlus.
Na co měřit kapacitu krystalu nevím? v datasheetu je uvedená "load capacitance", to jest vnější kapacita která je na krystal připojena.
Application Note 58: Crystal Considerations for Dallas Real-Time Clocks - http://db.zmitac.aei.polsl.pl/Electro ... irm_Docs/DALLAS/app58.pdf
Citát:Dallas Semiconductor does not recommend using crystals that do not have a CL that matches the RTC's
specification because this will decrease the accuracy of the clock. We find, however, that customers
sometimes choose to use 12.5 pF crystals with our 6 pF RTCs. For this situation it is possible to improve
the decreased accuracy caused by the CL mismatch. This can be accomplished by increasing the load
capacitance that the crystal “sees” by connecting a capacitor in parallel with the crystal as shown in
Figure 1. As a rule of thumb, the approximate capacitor value is equal to the specified load capacitance
(CL) of the crystal minus 6 pF (the approximate load capacitance of the real time clock oscillator circuit).
For example, if a 12 pF crystal is being used, a 6 pF capacitor should be placed in parallel with it to
improve the accuracy of the oscillator. A 12 pF crystal is adjusted by the crystal manufacturer to oscillate
at its specified nominal frequency when a 12 pF load is present. A 6 pF capacitor is therefore added to
the 6 pF load of the oscillator circuit to compensate for the additional load that the crystal needs in order
to oscillate at its specified nominal frequency.
No ne?
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