Doppler Shift Motion Detector
A motion detector utilizing Doppler Radar operating principles was constructed and added to the lab's inventory of experimental devices on 3/12/05. The schematic for the unit appears here:
(click on image for full resolution)
Theory of operation:
The network of Q3, Antenna, and C8 oscillates at approximately 1 Ghz by utilizing an 3/8" X 1/2" trace on the board which acts as the inductive component of a resonant circuit and extends from the junction of the D1 anode/antenna/C8 to the board's ground plane.
The Doppler frequency difference signal that results from the motion of nearby objects is detected by D1, which mixes the transmitted signal along with the received signal, producing both the sum and difference or Doppler frequency. The Doppler signal is input to pin 10 of U1, an LM324 quad op amp. U1D acts as a bandpass filter and amplifier. This narrower band signal is routed through potentiometer R8 which serves as a "sensitivity" or threshold control, and the adjusted signal is amplified by the remaining 2 op amps in the LM324. The network consisting of D2, R17, and C17 determine how long the unit's output circuit stays on after picking up motion, larger values of either R17 or C17 would result in longer turn - off delays, and smaller values would result in the opposite effect.
LED D3 is turned on when a "high" condition is present on the gate of MOSFET Q8, allowing current to flow from D3's cathode to ground.
There are plans to use this device after calibration tests are completed to detect, monitor and measure any Doppler Shift effects associated with the Stenger - Adams (SA) waveform applied to inductive circuits and motors.
Return to Motor Lab Internal Links