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I am wanting to fit a small camera that I already have to a quadcopter.

I have the camera working on the breadboard but the quadcopters battery is a 3.7v lipo. Supposedly the camera itself runs on 5v but seems quite happy with the 3.7v from the lipo. The line that switches the camera on and off alternates between a 3.3v and ground supply.

So initially it has 3.3v then you switch it to ground for 250ms and then back to 3.3v and recording commences. The same thing to stop recording.

Seeing as weight is a major consideration what is the lightest / easiest way to supply the 3’3 v for this function please and how exactly would I implement any suggestions. I thought of using a zener diode or level shifter somehow but I am unsure how to proceed.

Here is my Circuit:

enter image description here

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  • \$\begingroup\$ Can you turn the camera on and off by letting the yellow lead float and momentarily connecting it to GND when you want it to switch? \$\endgroup\$
    – EM Fields
    Commented Mar 9, 2015 at 10:20
  • \$\begingroup\$ Assuming that EM Fields hasn't nailed it, does the yellow lead have to go to 3.3V at idle, or is a lower voltage (say, 70% of 3.3V = 2.3V) sufficient? \$\endgroup\$
    – markt
    Commented Mar 9, 2015 at 11:05
  • \$\begingroup\$ I will have to investigate this situation. Unfortunately I do not any information on the specs of the camera other than what I have already provided. It is just a Chinese consumer item with very limited information provided on purchase \$\endgroup\$
    – Pedro147
    Commented Mar 10, 2015 at 2:35

2 Answers 2

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Depending upon the quadcopter controller, there might already be a LDO 3v3 regulator somewhere on the board. It might be good idea to reuse it.

If it doesn't work out, depending upon current draw on 'Yellow' control pin, a fairly large resistor with a parallel 3v3 zener could be used in a prototype/PoC attempt.

I'd probably explore other choices like LDOs before looking at zener option. While it sounds a bit cheaper, the zener keeps draining the battery even when the line is not in use. There are some fairly cheap LDOs available in tiny packages (e.g. http://www.newark.com/torex/xc6206p332mr/ldo-voltage-regulator-fixed-3/dp/18K7646 - may not be useful in this case, though).

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  • \$\begingroup\$ The LDO you linked to has a typical dropout voltage of 250 mV. That means it's only going to be any good down to a battery voltage of 3.55V. That doesn't allow much margin for the battery to discharge. Plus the device's maximum dropout voltage is 680 mV, which would render it not functional at all in this situation, but since this is a one off, and not a product we can ignore that. \$\endgroup\$
    – tcrosley
    Commented Mar 9, 2015 at 10:45
  • \$\begingroup\$ Vasu - I will have a probe around the board and see if I can find a 3.3v power source as this sounds like the best possible solution. Thanks \$\endgroup\$
    – Pedro147
    Commented Mar 10, 2015 at 2:41
  • \$\begingroup\$ @tcrosley: Agreed! I did not dig in to the datasheets. Your mentioned buck-boost converter might be the most fit in this case, assuming the board doesn't already have one. \$\endgroup\$
    – Vasu
    Commented Mar 12, 2015 at 11:08
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A Zener diode is not a good choice, because you would need to have a minimum Zener current of at least a few mA, which would be a continuous drain on your battery, and if your battery dropped below 3.3v, the 3.3v output would drop as well.

The correct thing to do is use a buck-boost converter, like the LTC3531-3.3, which takes any input from 1.8v to 5.5v and generates a 3.3v output. Compared to a lot of DC-DC regulators, it only requires three external components -- two capacitors and an inductor. It is available from Digi-Key.

enter image description here

If the spec for the camera says the voltage on the RED lead cannot be lower than the voltage on the YELLOW lead, then instead of a buck-boost converter you will want to use just a buck converter, such as the LM3670-3.3. Almost identical circuit. Also available from Digi-Key.

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  • \$\begingroup\$ I am sure that the buck converter option is a good one which I will look into thanks \$\endgroup\$
    – Pedro147
    Commented Mar 10, 2015 at 2:41

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