The design project was a handheld speedometer employing the doppler theory as its principle. An oscillator emits a microwave signal of about 1 GHz. As it encounters a moving object in its area of coverage, it is reflected bac to the antenna with a shift in frequency. It is a mized with the original signal and sum and difference frequencies result. The difference frequency is processed while the sum frequency is grounded. The difference frequency is made into a pulse and is counted on the duration of the programmable timebase. A programmable timebase is necessary to calibrate the speedometer to different units of velocity. The output is then displayed on 3 seven segment displays.
One major aspect of the design process concerns the oscillator section. Being a microwave oscillator, it uses some microstrips that act as an inductor at these high frequencies. With this reason, the whole oscillator section needs to be etched in a PCB to accommodate the microstrips. Simulation of the whole project, therefore, entails interfacing the PCB to the breadboard containing the counting circuit. There is still one more thing to consider in circuits operating at very high frequencies, lead lengths of components translates into stray inductances and capacitances that would affect the tuning of the transmit and receive antenna. To servce as an important reminder, lead lengths should be as short as possible to prevent tuning problems.
Keywords : Handheld,Speedometer,
Faculty/Department: Electronics and Communications Engineering
Degree: BS Electronics and Communications Engineering