Differences

This shows you the differences between two versions of the page.

--- guides:rfm22b [2013/08/16 11:17] – [Circuit Diagram] mbrejza
+++ guides:rfm22b [2013/09/04 10:15] (current) – [DominoEX] mbrejza
@@ Line 325: / Line 325: @@
 The RFM must be kept on TX all the time as the RFM22b's internal crystal oscillator circuit has a series capacitance that wanders according to the die temperature. For the best results it is better to have an external crystal and oscillator circuit which does not get affected by the changing capacitance.
-This circuit works by using the PWM output of the microprocessor, through a choke to remove the AC component and to pull the onboard crystal of the RFM22b via a varicap diode. The RFM crystal is only 30MHz and is multiplied up by approximatly 14.5 times. Since the tone spacing of Domino is only 17.5Hz at 434Mhz, the shift at 30MHz is in the order of only 1Hz per tone or about 20Hz total
+This circuit works by using the PWM output of the microprocessor, through a filter to remove the AC component and to pull the onboard crystal of the RFM22b via a varicap diode. The RFM crystal is only 30MHz and is multiplied up by approximatly 14.5 times. Since the tone spacing of Domino is only 17.5Hz at 434Mhz, the shift at 30MHz is in the order of only 1Hz per tone or about 20Hz total
 The varicap needs to be biased so that it is not being used at the bottom of its working range, so in the sample code the PWM is set to a minimum output level of say 100 and then the actual symbol is added to this.