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So are you referring to a single sensor output, or the difference between common axis sensors? In other words, when level, each of a pair of IR sensors outputs something around 1.6V?

Inside the IR module is two pairs of thermopile sensors and a dual instrumention OpAmp, nothing more. The rest of the work happens in their MCU module (the box that connects to the Rx). Four wires are used to connect the two modules: Pwr, Gnd, analog roll, and analog pitch.

The FMA implementation is clever. They have differentially connected two sensors together (one pair per axis) so that when both thermopiles see equal {but opposite} magnitudes of heat, the related instrumentation OpAmp outputs nearly 1/2 of the 3.2VDC rail. At other attitudes, the voltage slides up or down as a result of the ratio of the sensor pair.

The advantage of this is that only two A/D channels are needed to measure the four sensors. The alternative is to use four A/D channels and then perform the ratiometric mixing in software (different strokes for different folks). This would add two more wires to the interconnect cable too.

The altitude issue is a geometry problem. The IR ratio changes slightly as the point of reference changes. I just do not have any idea how serious the problem is at reasonable AGL heights. I am hoping it has limited impact. Cyber-Flyer's experiments seem to show otherwise. Either way, it is something that could be managed.

My concerns are really in other areas at this time. There is only so much I can do during the video retrace time. But I believe my little PIC can do it.

Edit: expanded Co-Pilot description.

Edited by Mr.RC-Cam
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I'll try to jump in. Please correct me if I am wrong.

So altitude introduces a gain error, but not an offset error.

That's correct.

Almost... there is never going to be perfectly good pair of sensors, so the level voltage is not going to be perfectly 0 (or whatever level you decide to call zero). And this small offset will drift. But besides this small drift the altitude or other atmospheric phenomena will not change reading at the level position.

If I've got it right, not sure why it's important

Let's say extreme case (which concerns me) that you've got your machine inside a cloud. The IR amplitude drops significantly and based on your ground calibration AI voltage tells you that you are at 5 degrees right bank. In fact you may be at 50 degree rigth bank and not know it. Unless you keep your aircraft perfectly level, there is no way of knowing the attitude. The device is no longer

"Aritifical horizon" but rather a binary level indicator.

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Oops, forgot to comment on these points:

Calibration is required to determine min and max thermal brightness so optimal gain can be calculated?

Yes. That is what the Co-Pilot's nose-down cal step does. The follow up servo wiggling indicates the dynamic range that is available.

Calibration for gain optimizes dynamic range but isn't required to eliminate offset from level.

The offset is corrected in another step. Model is held level then button pressed.

The artificial horizon will need to do these sort of cal things too. A three axis sensor would eliminate the gain cal step, but not the offset step.

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The device is no longer "Artificial horizon" but rather a binary level indicator.

Good point. As a matter of curiosity, what does the Co-pilot do when you go through heavy cloud cover. Does it try to put the model into a hard spin?

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Just want to add that I like where this thread is going. Although I truly appreciate the RC-CAM projects, very often what interest me more is the process of creating them much more then the actual final product.

Although I realize many just want to burn a PIC and don't really care what makes it work.

Cheers,

Mike

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The FMA system uses a "Z" sensor to calibrate the system for sky/earth temperature. This sets the sensitivity for local conditions and weather. They do not provide for additional "on the fly" calibration, but that doesn't mean that it can't be done. It seems to me that a calibration cycle could be innitiated occasionally, any time the net x-y sensor signals were reading zero.

T.I.

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It seems to me that a calibration cycle could be innitiated occasionally, any time the net x-y sensor signals were reading zero.

T.I.

Unless the calibration happens to take place while you are inverted ;)

Dave, the 'Z' sensor is a new offering by FMA that places a pair of sensors facing up and down. It allows you do do the initial field calibration of the co-pilot without having to hold the plane nose down... a nice feature if you are flying on a rather large airframe.

It also 'knows' which way is up, so if the plane manages to get inverted and you then turn on copilot remotely, it will roll the plane over with ailerons versus doing a high-G half loop.

Regards,

Bill

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Just the other day I wanted to keep my plane high and level for as long as I could. It was a small model and difficult to see at altitude. I could not tell quickly enough whether it was nose high or low. Wasted altitude and battery juice. Just then I thought to myself...I'm sure glad someone is working on an attitude indicator. :)

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The project's PC boards came in today. I stuffed one and everything fit just fine and it survived the smoke test. As far as SMT soldering goes, this board is not too bad since the layout is not jammed together. But, good eyesight or magnifier is a must.

In the photo you can see how big it is (that's a US quarter). There are some parts on the bottom too (one Vreg and seven R's and C's).

The labeled landmarks are:

A: FMA's Co-Pilot IR sensor module connector.

B: 5.0V to 10.5V DC power input (at some point the connector will be replaced with a wire pigtail).

C: Video-out to Wireless Tx.

D: Video-in from camera. There are four wires because the board can optionally supply regulated 5VDC to the camera.

I still have a lot of software to write, so it is nice to have a clean looking board to work from. If nothing gets in the way I'll work on it next week.

post-6-1083972071_thumb.jpg

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Thanks all for the kind words.

When do you think you can release the kit?

Is it possible to sell pre-programmed PIC with it?

I'm guessing it will be a few weeks before it can be released. I plan to offer a pre-programmed PIC and a 2-sided board. Maybe a full parts kit too.

But all this depends on how it works out. I still have a ways to go before I know for sure if this gadget will work at all. If not, then at least the journey has been interesting. ;)

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So, could this same hardware be used with different software to measure two analog voltages and overlay a digital readout over the video?

Yes, it can do that with careful coding. I'm planning to periodically display battery voltage.

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Mr. RC-CAM,

I can't wait to get the kit, so I ask some questions:

Have you tried to test your device and superimpose video image with moving tick marks?

I am concerned about delay time of co-pilot sensor with respect to actual position of the model. I've done some testing with my own version of AHI and co-pilot's data are clearly delayed compared to video. I am not sure where the delay is coming from (my "food chain" is much longer than yours) so I am curious about your results.

Edited by cyber-flyer
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Yes, I have enough working to see the tick marks move with the Co-Pilot. So far I cannot see a delay, but there is probably a little bit in there somewhere. I have a long ways to go, so I cannot say for sure how it will behave in the end.

I use a four point rolling average data set with a 15 Hz update. I tried for 30Hz update but the PIC's A/D is too slow to read both Axis' inputs within one video frame. So I ping-pong. If the data averaging makes it look too mushy or delayed then I can just eliminate that trickery.

If there is a noticeable delay caused by the thermopiles' IR response time then there is nothing we will be able to do. However, if it does exist then it must be minimal, otherwise FMA's Co-Pilot would be a real bear to get to work on some models.

Edited by Mr.RC-Cam
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The PIC's A/D is a 10-bit successive approx type. It takes about 2uS to perform a full conversion. However, when you change its 5:1 mux input to another analog channel, there is a penalty time caused by the internal holding cap's reset/charge period. This can take as long as 18uS, but depends on drive impedance of the analog source signal.

BTW, a mistake is in my last post. The A/D updates for the two IR sensors occur at a blazing 30Hz rate rather than the stated 15Hz (it was my 60hz attempt that failed). It's all plenty fast for the real time display of dancing ticks. ;)

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