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Chapter 6: Radio-Controlled Systems and Telemetr y 155

I connected the AR8000 throttle channel to pin 14 servo port, as was shown in Figure
6.20. I next ran the jm_freqin_demo program and started the PSerT application to view the
results. This is shown in Figure 6.22.
The displayed frequency of 45.4 Hz is equivalent to a period of 22 ms, which is computed
by taking the reciprocal of the frequency. The 22-ms value exactly matches the pulse rate I
measured using the USB oscilloscope. I was impressed with this outcome, since programs
often promise certain results but do not deliver on them. That was not the case here; the
frequency-measuring capability is very accurate. Just ensure that you keep the maximum
input voltage levels at or below 3.3 V, which is the Prop chip’s maximum allowable input.
The last section of this chapter deals with telemetry, which you will find very helpful
when operating your quadcopter.

Telemetry

The DX-8/AR8000 R/C system has an optional feature that provides telemetry in addition
to normal control functions. Telemetry is the automated transfer of data from the aircraft
back to the transmitter, which in this case, is also functioning as a receiver. The Spektrum
system provides for four data types to be sent via telemetry:

1. Battery voltage
2. Temperature
3. r/min
4. Altitude

Which data type is sent depends on the sensor used to create the initial data. Spektrum
utilizes a telemetry module named the TM1000. It is the core of their DSM telemetry system
and is shown in Figure 6.23.

Figure 6.23 The Spektrum TM1000 telemetry module.