I recently designed an infrared sensor board (dubbed “IRis”) for my friend’sDefcon talk. This video walks through the circuit design of the photodiode amplifier, and discusses some of the pitfalls associated with photodiode amplifier design.
Schematics, BOM, and KiCAD design files for the described IRis board are available on github.
I’s and Q’s and negative frequencies, oh my! Today we discuss mixers and frequency conversion, in particular, quadrature mixers and Tayloe detectors: what they are, how they work, why you might want one, and what do we use all this I and Q stuff for anyhow?
Today we look at how to generate a pair of quadrature signals from the output of a crystal oscillator using a pair of d-type flip-flops, as well as discussing the advantages and disadvantages of this technique.
BPSK31 has become a very popular digital communication mode among amateur radio operators due in no small part to its efficiency and narrow bandwidth. You can easily demodulate BPSK31 signals with readily available DSP software, or even using an Arduino.
Never the less, I thought it would be fun to build an analog BPSK31 demodulator that would output digital bits via simple two wire bus, and hit upon the idea of doing this relatively easily using amplitude demodulation.
Amplitude demodulating phase modulated data??
I know, I know, a proper PSK demodulator would implement a costas loop or similar phase detection circuit. This approach is a hack for sure, and won’t work as well as a proper phase demodulator, but has the advantage of being easily constructed with a hand full of “jellybean” components that are probably already sitting in your parts bin.