The Simple Tech Behind Hidden Camera Detectors

If you’ve ever been concerned about privacy in a rental space or hotel room, you might have considered trying one of the many “spy camera detectors” sold online. In the video after break [Big Clive], tears one down and gives us  an in-depth look at how these gadgets actually work, and their limitations.

Most detector follow the same basic design: a ring of LEDs through which the user inspects a room, looking for reflections indicating a potential hidden camera. Although this device can help spot a camera, it’s not entirely foolproof. The work best when you’re close to the center of a camera’s field of view, and some other objects, like large LEDs can produce similar reflections

The model examined in this video takes things one step further by adding a disc of dichroic glass. Coated with a metallization layer close to the wavelength of the LEDs, it effectively acts a bandpass filter, reducing reflections from other light sources. [Big Clive] also does his customary reverse-engineering of the circuit, which is just a simple flasher powered by USB-C.

[Big Clive]’s teardowns are always an educational experience, like we’ve seen in his videos on LED bulb circuits and a fake CO2 sensor.

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There Once Was An IC Dedicated To Blinking An LED

Today you can buy flashing LEDs; a simple two-lead component that requires only a power supply to produce even flashes of light. They look for all the world like any other LED, though embedded in the plastic dome is an integrated circuit to do all that flashing work.

There was a time though when a flashing LED was something of a big deal, so much so that National Semiconductor produced a dedicated chip for the task. The LM3909 boasted the ability to flash an LED for over a year using a single C battery. That part is now long out of production, so [Dillon] has implemented the LM3909 circuit using discrete components on a small PCB designed to take pins and fit the footprint of the original.

Why on earth might a reborn LM3909 be of interest to him, you ask? Well, he wasn’t able to make a 555 flash the LED from a coin cell, and a friend mentioned this chip which piqued his interest. The internal schematic is in the data sheet (found in the files section of his project), so he was able to implement it relatively easily using common parts. It still requires an external capacitor just like the original, but there is space on-board should you wish to put it there.

He’s produced a video we’ve placed below the break showing the device in action, proving it to be a drop-in replacement for an original. Recreations of classic chips using discretes are nothing new, we recently brought you a reborn PSU regulator chip made in 2014. An while you’re playing around with coin cell batteries, may we direct your attention to the Coin Cell Challenge.

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The Best Of Both Worlds: Arduino + 555 Should Confuse Commenters

Hardly a week goes by that some Hackaday post doesn’t elicit one of the following comments:

That’s stupid! Why use an Arduino when you could do the same thing with a 555?


That’s stupid! Why use a bunch of parts when you can use an Arduino?

However, we rarely see those two comments on the same post. Until now. [ZHut] managed to bring these two worlds together by presenting how to make an Arduino blink an LED in conjunction with a 555 timer. We know, we know. It is hard to decide how to comment about this. You can consider it while you watch the video, below.

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