Espritmodel.com Telemetry Radio
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Old Nov 14, 2012, 03:07 AM
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IR notes

Initial tests with the IR converted webcam were promising. It very nicely separates the IR led from an LCD monitor, ambient light, but not lightbulbs. The failure to convert the board cam but success of the webcam means no flashing is possible, but this eliminates the weight of an IR receiver. Still think the LED flashers using webcams are settling for a really slow update rate.

The IR led runs at 1.2V & 40mA. A 3.7V lipo gives a useful voltage to 3 IR leds in series. A 100R resistor powers 1 on 3.3V. In the worst case, 2 in series can be PWMed based on battery voltage. The need to maximize the brightness makes that most likely.

There's a slight chance a chroma key & comparison of neighboring blobs might eliminate lightbulbs. They would appear as a ring of red with white in the middle. The LED target would appear as a ring of blue with white in the middle. Eliminating blobs with neighboring red might work. Also, if multiple blobs are visible in the luma key, it could calculate the amount of red & blue in each blob, then take the blob with the most blue.

Otherwise, it's the same game of pointing all lightbulbs away from the camera & avoiding windows. Eliminating flashing should give faster updates. IR should also be the key to making Marcy 1 fly with the lights on.

The webcam reality makes it unlikely that the rasberry pi would be fast enough. There's going to be JPEG decompression at 640x480, which is a lot slower than RLE at 640x240. Dedicating a rasberry pi to the blob detection on each camera, then performing the autopilot on 1, would take some serious hacking. 1 would be an IP cam.

At least the software behind the webcams is much simpler than the software it took to read the board cams. No more multiplexing video with telemetry. No more luma keying on a microcontroller, trying to free up clockcycles for servicing the radio.

1 ARM is staying, because it's so much easier to generate the various PWM signals on it than an 8 bit micro. An 8 bit micro would be the target only if it was heading to a product.

But the board cams using visible luma keying are still needed in a ground rover. That uses blob detection to detect real patterns.
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Last edited by Jack Crossfire; Nov 14, 2012 at 03:14 AM.
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