![]() Given the first amplification stage has a gain of 510, this means there’s only 1.96kHz of bandwith “left” inside the LM258. – … while the LM258 has a gain bandwidth product of 1MHz! – Which leads to a total gain of 51000 (94dB) – Amplification on the first stage is 510 while the amplification on the second stage is 100 – I don’t see any reason for that 1nF capacitor when the high pass filter is done using the first op-amp – No high pass filter on the second amplifier (remember, the cutoff slope in the first amplifier stage isn’t vertical) Many many things are odd with this recommended amplification circuit: This is the (very low resolution) recommended amplification circuit that you will find online. Amplification Circuit from Chinese Sellers You may therefore be able to measure much higher speeds if the moving object is close to the sensor. Here’s the simulated amplification output generated using LTspice: However, this isn’t exactly true as the filter cutoff slope isn’t vertical. The high cutoff frequency is therefore set for a 24km/h or 15.4m/h speed. The InnoSenT application note allows us to put these frequencies in context: I’ll spare you the maths, the suggested amplification is 1018 (60dB) and a band pass filter from 3.4Hz to 1.06kHz. You’ll however notice that the op-amp positive input in our suggested schematics is tied to vcc/2, allowing us to have a centered amplification output as well.įrom the formulas above, we can compute the circuit total gain and cutoff frequencies. It consists in 2 cascaded inverting band pass filter circuits: The one you see above comes from InnoSenT. Now that I had traced the origins of this CDM324, I could find its recommended amplifier schematics. Finally, the advertised power consumption is identical to the HB100’s: up to 40mA 5V. The Radiated Power (EIRP) is more or less the same: 16dBm vs 15dBm. Specification-wise, the CDM324 antenna pattern is slightly narrower than the HB100’s: 80° azimuth and 32° elevation versus 80° azimuth and 40° elevation. I finally arrived to the conclusion that it likely is a clone of the InnoSenT IPM 165, which is itself very similar to the AP96 from Agilsense. I therefore spent several hours tracing the origins of this tiny sensor. Oddly enough, looking for “cdm324” on your favorite search engine won’t bring any interesting results. This motion sensor can easily be purchased on eBay under the name CDM324. Moreover, as the main frequency is higher the patch antennas are smaller, hence the tiny 25x25圆mm module. While the HB100 is using a 10.525GHz frequency, this new module uses 24.125GHz! This has the main advantage of being compatible with European regulations (ETSI #300 400) and having good penetration in dry materials. You may recall the article I wrote a couple of years ago about a nearly identical Doppler sensor, the HB100. This is the reason why a fire truck’s siren has a higher pitch when the truck is going towards you than when it is going away. I’m sure you’re quite familiar with the Doppler effect: you send an RF signal at a given frequency to a target, and if this object/person is moving the reflected signal’s frequency will be shifted. Arduino Tutorial Online Courses Video Training.Arduino Nano Projects List in PDF offline downloadable.Android based arduino Projects List Download PDF.esp8266 arduino projects list in pdf offline downloadable.Arduino Proteus Projects List for Download.Arduino UNO Projects List in PDF offline downloadable.Arduino Mega 2560 projects list in PDF offline downloadable.Arduino Complete Projects List PDF Downloadable.Huge List of tutorials & Components based resources.
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