Hack Correlation

I ordered a bunch of Digispark boards - for a few dollars each and included bootloader you cannot go wrong. They are basically prototype&forget boards and go under various other names (Picoduino, Pro Nano, Olimexino-85). Banggood.com has them for ~3$. The first project is an automatic power-on, power-off for an old Sony speaker set, formerly CD/cassette deck. My goal is for the amplifier to turn on when audio signal is detected and turn off after 30 minutes of silence. This is not so much for power saving as it is to reduce the white noise and GSM pickup during the night. The speakers can be turned on by connecting a 100 kOhm resistor between two of the four pins on a plug I've made various measurements to determine the correct input level that's reliably above the silence noise floor. In my case it was somewehere around 20mV. The ADC of ATTiny85 can be set to a 1.1V reference, improving the detection precision. Otherwise, by default, the 3.3V referen...

Note: modifying RF equipment is most likely illegal in all countries, unless you know your stuff! I bought 3 radio-controlled toy cars for parts and for racing around the house, since they were really cheap. Unfortunately, they all share the same RF channel (27MHz) which means you cannot use two at the same time. I mean, you could, but the fun of having two cars mirroring each other fades away after a few seconds. So I've wired the oscilloscope ground probe around the antenna to check the frequency and modulation. No surprise for finding out it's 27Mhz with some sort of OOK . Time to take the car apart to see what's inside: Notice the first hole on the bottom-right of the board surrounded by 4 soldered leads. That hole is for the adjustment cap, we'll make use of that later. The transmitter frequency is controlled by the 27.145 MHz oscillator, there's nothing to adjust there. The receiver frequency is in part control...

This is a continuation of the article from here:  http://hackcorrelation.blogspot.de/2014/12/central-ventilation-augmentation.html Take 2: I've decided to give the original unit a coat of fresh paint since it seemed to work pretty reliably - or so I've thought... The problem is that as the batteries drained the detection level changed, causing the unit to false trigger and quickly drain the 2xAA batteries within 1 day. Also it seemed to trigger falsely based on stray light level, time of day, planets' alignment, whether someone has showered or not...  So I've taken a look with the oscilloscope at the pins of the LED and decided that the capacitive detection method depended a lot of stray RF, making it highly unreliable. So drew up another schematic, this time using the LED as a photodiode (small voltage source). To get rid of having to tweak the constant in the code a small potentiometer (P1) was added - this has the effect of setting the light level:...