QCX assembly Rev 1.08
121
DVM and RF Power meter
The DVM and RF Power meter is implemented
using the 10-bit ADC channel 2 input to the
microcontroller.
When measuring voltage, connect the voltage to be
measured to pin 3 of the 3-pin DVM/RF Power
connector. The voltage is dropped by the potential
divider formed by R56 (3.3K) and R57 (10K). This
applies a division by a factor of 4.03. Since the ADC can measure voltages up to 5V, this means
the DVM function has a range of 0V to 20V maximum, and each ADC bit has a resolution of
0.02V.
When measuring RF power, connect the RF to be measured to pin 2 of the 3-pin DVM/RF Power
connector. In this case D4 and C42 form a simple RF detector. The RF is rectified by D4 and
smoothed by C42. R56 (3.3K) and R58 (10K) again form a potential divider that divides the
rectified voltage by a factor of 4.03. The resulting range of the power meter is from 0 to 5W
approximately.
For normal operation of the radio, if you wish to see a battery voltage icon on screen, then connect
pin 1 to pin 3 of the 3-pin header. This connects the voltmeter input to the 12V supply of the radio.
In the unlikely event of accidentally overloading the RF power input or the DVM input, the 10K
resistors R57 and R58 limit the damage to the ATmega328P processor or maybe prevent damage
altogether. Perhaps. (don’t feel tempted to try it intentionally).
Audio ADC
There are two audio connections from the receiver signal chain to the
microcontroller. One is connected at the output of the I-Q balance
adjustment potentiometer. In other words, the input to the CW filter.
The second audio connection is connected after the final audio
amplification gain stage. Both of these audio signal channels are fed to
Analogue to Digital Converter (ADC) inputs of the microcontroller.
The circuit diagram (right) shows the circuit at AUDIO 1 (ADC channel
0) which is connected to the audio amplifier output. A duplicate circuit is
used on the other channel. The purpose of the circuit is to remove the DC bias from the audio
signal, and apply a new bias of 2.5V, to bias it to the middle of the ADC’s input range. The 1K
resistor in series with the ADC pin is intended to provide some kind of limited protection to the
microcontroller in the event that the voltage falls outside the range 0-5V.
The ADCs in the ATmega328P have 10-bit resolution which translates to about 5mV. The ADC
conversion result is a number in the range 0-1023, with 512 representing zero. An audio voltage of
+/- 2.5V can therefore be measured. In practice, the audio signal is much less than this, which
means the full ADC range is not really used. The AUDIO2 channel (connected at the CW filter
input) has even less amplitude so is not used for anything except the BPF Alignment procedure,
which has a very strong signal.
Содержание QCX 5W CW
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