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A LOOK AT THE RCWL-0516 3GHz MOTION MODULE by Allan Linton-Smith A radar for $2? Yes, indeed. You may recall our description of this little ‘El Cheapo’ module in the February 2018 issue. It’s intended to be a motion detector, like a PIR sensor but with radio waves instead of infrared. Here we take a deeper dive into its operation and describe a few modifications you can make to change its behaviour. T hese modules are so cheap that you might as well buy a few to experiment with. You can turn on lights automatically, make burglar alarms, detect the movement of animals… if something moves, you can detect it with this little beauty! It can detect movement behind thin walls. It’s hard to believe that you can buy a tiny radar module so small and cheap that can detect movement within a seven-metre radius and operate a relay in response. One of the major differences between radar and passive infrared (PIR) detectors is that this radar module will detect the movement of any object larger than about 10cm2. In contrast, an IR detector will generally only detect movement of an animal or human, or perhaps lightning activity. The module As mentioned above, we described its operation in the February 2018 issue, starting on page 44 (www. siliconchip.com.au/Article/10966). We’ve reproduced the circuit here, as we will discuss its operation in more detail; it’s shown in Fig.1. Now we will unravel its secrets and show you some additional tricks! The module itself is about the size of a postage stamp at 17 x 36mm (and, 48 Silicon Chip The Elecrow RCWL-0516 Motion Detector, shown here close to life size, is available online from a variety of sources from just $AU1.65 including postage! unbelievably, not that much more expensive!). It operates from 4.5-24V DC with a quiescent current of 2.6mA. It has five terminals (CON1) for connection to a power supply, an output to trigger a relay, a 3.3V output and a terminal for the connection of a lightdependent resistor (LDR). The LDR can be used to disable its operation depending on the ambient light level. This was explained in more detail in the 2018 article. A small modification will allow you to send audio-level signals to an amplifier/oscilloscope/data logger for analysis. It can also be adjusted for sensitivity and on-time by adding two extra components. With a simple modification, you can even view the motions of moving objects on an oscilloscope or plot them on a data logger. Or listen to them via a frequency multiplier. The circuit Referring to Fig.1, note that there Australia’s electronics magazine are a few different versions of this module floating around, and the one we’re describing here has some slight implementation differences compared to the one described earlier. But they function in pretty much the same way. The differences are shown in green and with dotted lines on Fig.1. NPN transistor Q1 is the heart of the radar module and acts as a 3GHz oscillator, receiver and mixer. The PCB track antenna transmits and receives the signals. If a moving body comes within range, the reflected signal frequency changes due to Doppler shift (by a factor related to the body’s approach speed) and this is mixed with the transmitted signal, resulting in sum and difference products. These cause a voltage variation across Q1’s emitter resistor, sufficient to trigger a positive pulse at pin 2 of U1, which goes to the OUT terminal of CON1. Capacitors shown in red represent the parasitic capacitances of Q1 and are necessary for the correct performance of the oscillator. One of the innovative features of this radar circuit is that Q1, a 3GHz wideband transistor, acts as a multipurpose component. On my module, it is marked as siliconchip.com.au 100 4.7k 100nF 3x 100nF C CB B 1pF 2.2k Q1 MMBR941 (BFR620) E (BFR1 8 3) C 0.4pF C BE +3.3V +3.3V C CB, C BE AND C CE ARE INTERNAL TO Q1 10nF 1M C CE 12 0.2pF 13 16 22k (33k) INDUCTOR/ ANTENNA FORMED BY S-SHAPED PCB TRACK 22 F R–GN* 10nF VALUES IN GREEN ARE ALTERNATIVES 22k (18k) FOUND ON SOME MODULES SC 220 (2.0k) 33pF 56k A 22 F Vdd 2OUT RR2 2IN– RC2 1OUT RR1 RC1 1M 15 1.0k 33pF 1nF 22 F 100nF 1IN– VO VC IB 1IN+ 6 1M 1M 5 3 10k 10nF CON1 4 +3.3V OUT 1 10nF U1 RCWL-9196 VIN 14 R–CDS* 11 1 C–TM* (1.0k) 100 2 2 8 OUT 4 9 OUT 1M 1 0 0nF VIN 5 U2 7 133-1 10 Vss 7 GND 3 CDS IN GND 1 0 0nF CDS* 2020 * OPTIONAL Fig.1: the complete circuit of the RCWL-0516 microwave radar motion sensor module. The track inductor forms the antenna for both transmission and reception of microwave signals and has a range of approximately 7m. “1N2”, and its origin is China. It is an oscillator, transmitter, receiver, amplifier and mixer, and also provides capacitances necessary for the oscillator and feedback. This transistor’s base is held at approximately 1V by the three resistors connected between its collector, base and ground. The 3.3V supply is decoupled by three 100nF capacitors at its collector and one across the base divider, which forms an RC low-pass filter in combination with the 100resistor. The oscillator circuit operates at close to 3GHz, set by the resonance of Q1’s collector-emitter capacitance (about 0.2pF) and the antenna inductance (0.014µH). The capacitance of the transistor is given by the manufacturer’s data sheet. Simulation confirms that this configuration will oscillate at 3.007GHz with a Q of 1.1 – see Fig.2. Performance We measured -23.51dBm or 4.5µW (microwatts) at 3.010GHz continuous- ly transmitted output power. This was measured with a 3GHz antenna connected to a spectrum analyser, with the module very close to the antenna (see Fig.3). While this seems like a small amount of transmitted power, it is strong enough for an effective range of 7m under normal conditions. The good news is that it is not strong enough to cause any interference with other devices. It does not even seem to interfere with identical radar modules, although the oscillators vary quite a bit due to variations in the transistor performance and component tolerances. The fact that the detector is only activated by the differences between the transmitted and received signals means that the oscillator does not have to be drift-free. This makes the module much cheaper compared to a device with a PLL or YTO (Yttrium-iron-garnet Tuned Oscillator. Antenna Fig.2: a simulation of the module’s oscillator. The predicted frequency of 3.007GHz is very close to the measured frequency. The frequency varies due to temperature, supply voltage and other variables. But only the frequency shift due to motion matters, so that doesn’t affect its operation. siliconchip.com.au Australia’s electronics magazine The antenna is actually a snakeshaped curved trace on the circuit board which has been tweaked using a series of tiny holes. The antenna is therefore multitasked as a transmitter, receiver and inductor. There is also some capacitance designed into the PCB by way of overlap with tracks on the underside and a small circle which acts as receiving antenna. The transmitter is actually a Colpitts December 2020 49 Fig.3: we measured a continuously radiated power of -23.51dBm at 3.010GHz, which equates to around 4.5 microwatts. The peak ‘dances’ around the centre frequency when moving objects are nearby. oscillator with feedback tapped between the 0.4pF and 1pF parasitic capacitors of Q1. These capacitors are the internal capacitance of the transistor CCB and CBE respectively, and are shown in red on the circuit diagram. A small amount of stray capacitance on the PCB from the three overlapping tracks has a small effect on these values. It has also been suggested that the circular pad on the underside of the module is also part of the LC oscillator and is “inserted” between the base and collector. Still, judging from its size, it is primarily intended as a receiving antenna, to assist with the efficiency of the overall package. The selection of the transistor is important both in terms of its highfrequency cut-off and its internal capacitance. When there are no moving objects in its range, Q1 oscillates in a steadystate with a 1.0V bias on its base. It draws a relatively constant current, Fig.4: the signal at pin 12 of U1, ie, Q1’s emitter voltage after the low-pass filter. We waved a broom around two metres from the radar module behind a thick shield, triggering the module. which provides a constant voltage of approximately 0.4V across its emitter resistor. Once an object moves within its range, the reflected signal is picked up by the antenna and mixed by Q1. This creates a fluctuation in the mixed signal amplitude and a corresponding voltage fluctuation across the emitter resistor, which increases to about 0.8V peak. This is shown in Fig.4. This voltage is fed to pin 14 (1IN+) via an RC low-pass filter with a -3dB point of around 159kHz, to remove the 3GHz carrier. Note that there is a bit of a delay between the movement and the output being triggered, probably due to onboard filtering to prevent EMI and other brief transients from triggering the unit. This delay amounts to about one second. Output pin 2 remains high for around three to five seconds (or until movement stops). The signal at the OUT terminal of CON1 can be used to power LED(s), trigger a relay (via a relay driver ar- rangement) or into a digital input on an Arduino, Micromite, Raspberry Pi etc. The chip, U1, is marked RCWL9196 which is almost identical to a BISS0001. This is a commonly used IC for passive infrared (PIR) detectors. It’s a CMOS bi-directional level detector with excellent noise immunity and was originally designed to trigger alarms from IR detectors. It features power-up disable, output pulse control logic and selectable retriggerable/non-retriggerable modes. In this module, it is configured to activate for three seconds when it is triggered and then reset automatically (ie, it is set in re-triggerable mode). Component layout The component layout on the top of the module is shown in Fig.5; there are a few components on the underside also, primarily regulator U2 (a 7133-1 low-dropout linear regulator). U2 was not present on the original board from Elecrow that we described Fig.5: RF transistor Q1 is on top of the board, which supplies the outgoing signal via the snakelike antenna from its emitter. This antenna also receives reflected signals. 50 Silicon Chip Australia’s electronics magazine siliconchip.com.au REG1 7805 K D1 1N 4148 470kW 10kW 2 4.7mF 1.5mF 470kW A 3 15 8 1 IC1a 14 3 1MW K D2 1N 4148 PHASE COMPARATOR & VCO 22n F 100kW A I NP U T 100kW OUT 16 SIGin COMPin 6 7 C1a C1b IC2 4046 100kW 100kW VCO 4 out PCout VCOin R1 13 9 8 11 1MW INPUT BUFFER/ SCHMITT TRIGGER 100mF 16V 10kW IN K GND S2 +9-12V A 100mF 16V 100kW OUTPUT BUFFER/ SCHMITT TRIGGER 6 5 R2 12 D3 1N4004 220W 7 IC1b OUTPUT 1.5mF 4 100kW 1.8MW 100kW 1.5mF S1 Fig.6: a slightly modified version of the Circuit Notebook entry “Frequency multiplier for LF measurements” from the February 2004 issue (p71). It uses phaselocked-loop (PLL) IC2 and dual decade counter IC3 to multiply the frequency of the incoming signal by a factor of 10 or 100x, depending on the position of switch S1. x 100 100n F in 2018. Instead, the VIN pin of CON1 was wired to pin 8 of U1, the input to its internal 3.3V regulator. That board also had two 100-150nF bypass capacitors on that line, while this one has a similar pair of capacitors at regulator U2’s input and output. Also, Q1 was an MMBR941 on the previous board, rather than the BFR183 used on this one. Presumably, the three alternatives for transistor Q1 are all very similar or else the oscillator would not work correctly. There are a few other minor component value differences, but otherwise, the modules seem quite similar. U2 provides the +3.3V rail. The advantage of external regulator U2 is that it allows for more current to be drawn from the +3.3V output at CON1 by external circuitry. But it does limit the maximum supply to 24V rather than 28V. C-TM R-GN R-CDS siliconchip.com.au x 10 IC1: LF353, TL072 IC3: 4518 1N4148 16 CP1 10 9 IC3b CP0 15 8 MR O3 O2 O1 O0 14 13 12 11 1/ 10 CP1 2 A 1 CP0 7 MR O3 O2 O1 O0 6 5 4 3 IC3a 1N4004 A 1/10 If a lot of current was drawn from the 3.3V rail, U1 could overheat, so having it supplied by a separate device is probably a good idea. By the way, one of the few differences between the RCWL-9196 IC and the BISS0001 it is supposedly a clone of is that pin 8 has an entirely different function; here, it goes to the internal voltage regulator, whereas on the BISS0001 it is the reset and voltage reference input pin. K K Connecting it to an Arduino or Micromite We covered this in detail in our February 2018 article, but as it’s quite simple, we’ll go over it quickly again. Just connect GND and VIN on CON1 to GND and 5V on the micro board respectively. Then connect the OUT pin of CON1 to a digital input on the micro, such as D2 on an Arduino, ESP8266 or ESP32. Making modifications Connecting it to something else As we explained in our earlier article, an SMD resistor can be soldered to the pad marked “R-GN” to lessen the sensitivity, so that it only triggers at close proximity. A value of 1Mwill halve its sensitivity. There is also a pad marked “C-TM”; adding a capacitor here will lengthen the on-time at VO (pin 2); a 10nF capacitor will roughly double it. You could feed the output of this module to our Opto-Isolated Mains Relay (October 2018; siliconchip.com. au/Article/11267) to switch just any mains-powered device on when motion is detected. With some simple modifications, that same project could also be used to switch low-voltage DC at reasonably high currents. Alternatively, a simple transistor 3.3V GND OUT VIN CDS Fig.7: on the underside of the board there is a regulator (U2) as well as three locations for optional components: R-GN to adjust the gain, R-CDS for light sensing, and C-TM to increase the on-time. Australia’s electronics magazine December 2020 51 VCC 1N4 004 (NOT REQUIRED FOR LED) SUITABLE RELAY (OR LED) D PIN3 CON1 G S IRF540 etc can be added to the output of the module if you wish to operate a high powered LED or drive the coil of a relay, as shown above. The simplest way to do this is to use an N-channel Mosfet like the IRF540. Connect its gate to pin 3 of CON1 (OUT) and its source to pin 2 (GND). Its drain can then drive the negative terminal/cathode of the high-power LED or other low-voltage DC device, with the device’s positive terminal/ cathode connected to the 12V DC (or similar) supply. If the device is a relay, it’s also a good idea to connect a 1N4004 diode across its coil, with its anode to the Mosfet drain (negative) side. Listen to moving objects! One of the more interesting ideas for this module allows you to hear moving objects by using a frequency multiplier. The signal from pin 12 of U1 is an amplified version of the signal that was fed into pin 14. This then goes to the input of a frequency multiplier (circuit shown in Fig.6) and its output is connected to a small audio amplifier and an earpiece. For the audio amplifier, you could use our version of the popular Champ project (February 1994; siliconchip.com.au/Article/5303) or its more recent update, the Champion (January 2013; siliconchip.com.au/ Article/1301), which also incorporates a basic preamplifier. Each moving object has its own characteristic, so could possibly be of use for the vision-impaired, to help warn of fast-moving objects, vehicles or even stationary objects which can be detected by walking up to them. The frequency multiplying circuit uses a PLL and can be set to 10x or 100x. It requires an input of at least 0.8V RMS (2.25V peak-to-peak). Most of the signals from pin 12 of U1 are infrasonic; for example, when I was waving a broom, the resulting signal was around 3Hz. This cannot be heard directly, but when multiplied by a factor of 100, Useful links and videos: • www.codrey.com/electronic-circuits/ microwave-radar-motion-sensorswitch/ • www.rogerclark.net/investigatinga-rcwl-9196-rcwl-0516-radar-motiondetector-modules/ • https://youtu.be/rgVu9n_j9pM • https://youtu.be/9WiJJgIi3W0 • https://youtu.be/Hf19hc9PtcE it becomes a very audible (but weird) 300Hz signal. You can listen to some examples here: www.siliconchip.com.au/ Shop/6/5501 Summary This innovative little module is a very efficient design, uses just a few components to keep the cost and size to a bare minimum. You can have heaps of fun playing with this radar without having to spend much dosh, and it’s also very safe to experiment with. There are countless applications for this clever little module, examples of which can be found all over the web! SC LAST CHANCE FOR CHRISTMAS 2020! Want to have the brightest Christmas ever with our superb LED Decorations (see November issue)? Wow! We can’t believe just how popular our LED Christmas decorations have been! We’ve sold HUNDREDS of kits and they’re still racing out the door. But time is short: you’ll need to get in really quick to have these little beauties ready to brighten your Christmas – not just time for us to get them to you but time for you to build them! RED SLEIGH red rEINDEER red tree green tree white tree red cap red green sTockING sTockING red CANE WHITE STAR RED bauble YELLOW bauble GREEN BAUBLE BLUE BAUBLE ALL THE KITS ARE THE SAME PRICE: Just $14.00 each inc GST (plus P&P -- $10 per order). Buy one kit or buy lots for sensational displays! Simply order the kit for the decoration you want (easiest and quickest via www.siliconchip.com.au/xmas2020 www.siliconchip.com.au/xmas2020). The kit will include all non-optional parts: the pre-programmed PIC12F1572-I/SN for that decoration, the appropriate PCB, required resistors and a mix of twelve red, white and green LEDs (so you can choose the pattern you want) plus the button cell holder (but not the button cell). Or choose the giant RGB stackable LED Christmas Star . . . Also from the November 2020 issue, our giant (194 x 185mm) RGB LED Christmas Star will take pride of place on your tree (or anywhere Just $38.50 each inc GST else!) this Christmas (and for years to come). Kit includes PCB, (plus P&P – $10 per order) programmed micro, 30 RGB LEDs and all other non-optional parts. ORDER NOW AT WWW.SILICONCHIP.COM.AU/SHOP 52 Silicon Chip Australia’s electronics magazine siliconchip.com.au