I have been thinking on the possibilities to use external clock source for my ATTiny84 projects for some obvious reasons. Using the internal oscillator works great in most cases, but may not be so accurate in some applications (IR,RF) as it depends on the VCC and temperature. You can measure both in the code and adjust oscillator’s calibration, but isn’t that too much? On the other side, the CLK pin of the RFM12B module can be set to output the clock frequency, programmable to 1-10Mhz. It defaults to 1Mhz upon reset (given CLK output is enabled), and the ATTiny can change that to whatever it needs: 1.0,1.25,1.66,2.0,2.5,3.33,5.0,10.0 MHz .See the RFM12B configurator by JeeLabs for concrete configuration values, Low Battery Detect and µC Clock section.
There has been an ancient topic regarding this in a German forum, quite useful stuff, confirming this can be done easily.
The ATTiny84V (Modification V) that I use will happily work @10Mhz down to 2.7V, so we have perfect match.
So I am thinking of creating a Funky version that can utilize the CLK from RFM12b, this will be entirely optional, as you can set the fuses to work off the internal oscillator at any time. Would there be interest in such “Funky”? I’d also be interested to hear particular reasons for needing precise timing and why the internal oscillator is not good enough.
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