A simple LED transmitter, and LED receiver!

Tonight’s 20 minute electronics project was to create a simple transmitter to send music using light. A trivial circuit modulates the current through an LED, and a different LED serves as an (inefficient, and not very good) light sensor. Normally you’d use a selenium photocell or the like, but I couldn’t find one in my junk box, and Radio Shack doesn’t have ’em anymore. But LEDs will generate a small current when exposed to light, so you can actually use them as a photodetector.

Addendum: The audio in the video above is pretty weak (the microphone on the iphone is located at the bottom of the phone, and isn’t ideal for recording low level audio). So, I went ahead and recorded a small sample using the voice memo application on the iPhone, and holding the microphone much closer to the speaker of the amplified speaker to give you a better idea of what the quality is. I also reduced the value of the input filter cap to just 4.7uF, which seemed a bit better, and also put in another 4.7uF cap in series with the sensor LED. I’m not sure that helped, but the levels and sensitivity seemed better. At the very least you should be able to hear the audio quality more clearly.

Audio from my LED Transmitter/Receiver (MP3)

Addendum2: The guys over at the Make Blog had some more good information about using LEDs as light sensors.

The Broadcaster Project, revisited

One year ago today, I first published a link to The Broadcaster Project, a site which had several tips on using command line tools such as ffmpeg to assemble videos. I use a similar technique to do my more recent videos: I take the raw footage from the camera and resize it, denoise it, and add some overlaid text before uploading it to YouTube. Revisiting The Broadcaster Project, I see they have a few more recipes that can be useful, such as ones for assembling time lapse movies and the like. I also found a reference to youtube-upload, a command line python script that can automatically upload videos from the command line, a part of my process that I still did with the web interface.