Development of an ARM7 avionics based Quadrocopter AP platform (Q4Arm7)

[Arthur P.]

I-ve just started a thread on the above in the Aerial Photography Forum here: http://www.rcgroups.com/forums/showthread.php?t=706878#post7719491. Reason to post it in that forum is the currently still limited interest in this flying craft and the fact that the main intent for it is RC Aerial Photography / Video. However, as it is also a VTOL, involves significant Electronics development, and will also certainly evolve some UAV characteristics for specific types of AP, I'm cross-linking from here.

[Arthur P.]

I just got my Parallax USB oscilloscope today and immediately did some testing on a Spektrum AR7000 receiver, opening up the housing of the main unit. The satelite unit of course contains a 2nd receiver board and is connected to the main unit with 3 wires. That had me baffled a bit as I2C would be expected to have 4 wires, SPI 5 or 6 wires.

In the main unit there is this same little satelite board with the CYWUSB transceiver and a small 2nd processor chip. It is connected to the main board with three pens. Moving from the side of the board inward the pens are indeed PWR and GND (or GND and PWR, didn't really check the sequence), with the pin farthest on the side being signal. And this is definitely a fully digital signal of bits. So most likely just a single serial line going to the bigger chip on the main board. This must be doing some comparison of the data received by the two receives an then transforming the correct bytes to the PWM signals on servo headers 1 through 7. Signal pins there are showing a 1-2ms wide signal (depending upon stick position), so that's as expected.

The power header is interesting though. Here there is a 700 microsecond burst of 7 spikes, each being something like 15 microseconds long, roughly in synch with the 1st PWM signal. It definitely is not digital bits and bytes. It could be a PPM type signal, but it certainly is nowhere near the 20ms I would have expected. Anybody have a clue? Could they be outputting a very high condensed PPM signal on this signal pin?

Attached a (poor quality, sorry) screen shot of the start of the PWM signal on channel 1 and the burst on the signal pin of the power header.

[AndyKunz]

You only need 1 wire to communicate. The other two can be power and return.

It would help if we were to know what the other channels were all doing. Also, do you think you could try getting a resolution where we can actually read the screen? Use the screen-print function instead of a camera. (Alt-PrtScr works great).

Andy

[Arthur P.]

All channels were neutral other than throttle which was at zero. I-ll try and get a better pic this weekend.

I read somewhere that some receivers bring out the PPM signal to the signal pin on the battery connector. But I would expect the PPM train to be a bit longer than about 700 micrseconds. In other respect it could be, but why shorten it to this degree. Wouldn't help accuracy of decoding at all.

[Arthur P.]

Sorry, but I haven't had time to get a better picture of the trace yet. Nor any further measurments.

Anybody ever take a Spektrum AR7000 apart?

The main print has 5 interesting connection pads at the top which would fit a standard 0.1 inch row of pins. They're not used. But I assume they mean something, e.g. may be used for factory testing. Could I be so lucky as to have an I2C or SPI connection to the combined / analyzed / corrected Rx signals there ??? Wonder whether anybody has ever checked.... I won't have time to do any testing until Sunday or so.

[AndyKunz]

Most likely for factory programming of the micro and/or testing/calibration of the RF circuitry.

Andy

[Arthur P.]

One pad is 3V, one ground and the others don't seem to carry any active signal. 5-pads: maybe an SPI interface for programming?