Sunday, October 11, 2015

FPV with Hubsan H107L - fail!

I got a Hubsan H107L quadcopter (or a clone thereof) from a friend. I've been flying it quite extensively lately, and thought it would be cool to try some FPV on the thing.

I tested the carrying capability of the thing by attaching some self adhesive wheel balance weights on its bottom. Turns out it can only lift about 15 grams, so any video gear needs to be really light.

I ordered the smallest cheapest camera I could find on eBay as well as the smallest video transmitter. Although the copter is controlled over 2.4GHz and the small video transmitters are also 2.4GHz I decided to give it a try anyway.

Figure 1. The small camera straight off from eBay.

According to the data sheet, the video transmitter board operates from 3.3V to 5V, so operation from the single LiPo cell of the quadcopter is possible. The camera however was specified for operation from 9 to 12 V. Opening the camera revealed a single low dropout linear regulator providing 3.3V to everything important (only the bias voltage for the small electret microphone was fed from the supply voltage). The dropout voltage of the regulator was around 0.5V, so power could still be supplied from a single cell as long as it wasn't too empty (also the camera remained operational long after the regulator dropped out of regulation). As a side note, the specified 9V is probably too high for the camera. As it draws about 200mA of current, the regulator needs to dissipate about 1 watt of power. That is quite a lot for a SOT-23-6 package.

By coincidence the video transmitter is exactly the same size and shape as the camera board, so both of them fit inside the camera housing. It was then just a matter of connecting the boards to each other and wiring the power. The whole set-up weighs just 10 grams.

Figure 2. Camera and transmitter boards connected. Yellow loose wire is the antenna, while red and black are the power leads.

Figure 3. Camera and transmitter boards fitted in the camera housing. A small hole was drilled for the antenna wire.

Unfortunately, with the high power video transmitter so close to the quadcopter receiver, the control range is reduced to just 2 meters. Switching the video transmitter channel doesn't affect the range, so the high power is probably just saturating the receiver. Complete failure in that respect. You can't win them all. Perhaps I'll find some use for this neat little camera later.

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