If you follow Limpkin’s blog, you may have noticed that this is their third project using doppler sensors, and the second with the CDM324. This tiny sensor is just so neat for its price!
I learned quite a few things about electronics since I first made that amplification circuit for the CDM324 6 years ago.
Here are the main changes implemented in this new version:
– using an FFT to extract the measured speed from the CDM324 output
– using an automatic gain circuit to increase the detection range
– adding an onboard speed display for reading convenience
The previous CDM324 amplification circuit had 84dB of gain which in some cases was not enough. Instead of two fixed gain stages, I’m now using one fixed gain stage and a variable one for up to 92dB of gain (or 40000x voltage gain!). This second gain stage has automatic gain control, automatically varying the overall gain between 72dB and 92dB.
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