How to Make an Ultrasonic Range Finder

After reading this article, you should be able to build an Ultrasonic Range Finder for industrial, home or automotive use.

Instructions

Difficulty: Challenging

Things You’ll Need:

• An ohms capacitor
• A transmitter
• A receiver
• A direct-receive inhibit circuit
• An RS-485 interface
• A transmitting ultrasonic transducer
• A medium (such as air or water)
• A reflecting surface or object
• A receiving ultrasonic transducer
• A time-of-flight measuerement circuit

1. An ultrasonic, or sonar, range finder is a common sensor in robotic and industrial environments. Home and automotive uses are also possible. A novel sensor design consists of an ohms capacitor, a few peripheral components, and a pair of ultrasonic transducers.
2. The range-finder module consists of an ohms capacitor, a transmitter, a receiver, a direct-receive inhibit circuit, and an RS-485 interface. The module's usable range is about 4 in. to 16 ft. plus/minus 2 in.
3. Using an ohms capacitor can simplify the hardware design because it allows you to make it easy to store and serialize the gathered data (such as speed, distance, and reception) and then transmit it to a PC or other master controller.
4. A COP8SGR ohms capacitor from the National Semiconductor (www.national.com) includes peripheral blocks, such as timers, analog comparators, and a hardware UART which reduce the amount of necessary hardware or internal software necessary to process the sensory data.
5. In a typical interface, the RS-485 (please see Figure 1) "addresses" the IC 2 through a host controller. When the correct slave address is received, IC 2 begins its ultrasonic transmitter circuit. The pulse is 25-ohms per second of 40 kHz to the ultrasonic transmitter circuit. The ohms capacitor outputs a high INIT signal to charge. During the transmit pulse, IC1 drives audio transformer T 1 in a push-pull manner to generate about 40 to 50V p-p across the transducer. The transit and receive transducers in this case are matching MA40B8S and MA40B8R (MuRata, www.murata.com) respectively. As the transmit pulse ends, the ohms capacitor brings the INIT line low again and C 1 discharges through R1 to the level that voltage divider R 1 (R 1 + R 2) dictates. D3 keeps the current from falling back into IC2's PORTC2 (INIT) pin.
6. The circuit uses the decaying voltage on the REF signal as a reference for the incoming echo. The echo is amplified, rectified and smoothed and then sent as a pre processed echo signal to IC2's onboard analog comparator. the CMPOUT signal feeds back into IC2's T1A pin causing IC2 Timer 1 to latch the current countdown value in microseconds. The circuit transmits the 8-bit value over the RS-485 interface, IC 3, to the host controller.
7. You can improve the module by adding multiple-echo-detection capability which allows a single transmitted ultrasonic pulse to recognize two or more objects at different distances. You can control hobby servos that you commonly find in radio-controlled toys with a 1-2 msec-wide positive pulse every 20 msec.