Differences

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--- guides:rfm22b [2012/12/29 16:59] – navrac
+++ 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 on chip 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 the PWM is set to a minimum output level of say 100 and then the actual symbol is added to this.
+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.
 The code example also reprograms the timer counter so that the PWM is 8 bit fast mode so that the pwm frequency
@@ Line 333: / Line 333: @@
 ==== Circuit Diagram ====
-note: Make sure the potentiometer is a multi- turn type as quite fine adjustment is necessary.
-{{:guides:domcct.png?200|}}
+For a full description see [[guides:crystal_pulling|Crystal Pulling]]. The sensitivity of the circuit can be reduced by reducing the value of C2
+{{:guides:crystal_pulling_rfm.png|}}
 ==== Code ====
  note: Since the Timer counter is being used for fast pwm, software serial cannot be used to talk to the GPS.
@@ Line 514: / Line 515: @@
   * Turn down the volume as the sound is like two squirrels in a bag and gets rather irritating after a short time.
   * move the cursors over the tones as per the picture below.
-  * Adjust the potentiometer so that the overall width of the tones are slightly outside the red lines.
+  * Adjust the potentiometer so that the overall width of the tones are just inside the red lines.
   * Keep adjusting till the message becomes readable.