SensComp 6500 Series Ranging Module
Description: The 6500 Series is an inexpensive SONAR ranging module that can drive all SensComp electrostatic transducers with no additional interface. SensComp, formally known as Poloroid, can be found at : http://www.senscomp.com This module has an extended range of 6 inches to 35 feet. This was formerly made by Polaroid, which is now known as SensComp.
This module, with a simple interface, an extended range and typically an absolute accuracy is (+-) 1% of the reading over the entire range. This module has an external blanking input that allows selective echo exclusion for operation on a multiple-echo mode. The module is able to differentiate echos from objects that are only three inches apart. However, as the speed of sound is inversely proportional to the medium through which it travels, such as 348 meters/second at sea level when it's 21 C/70 F. The digitally controlled-gain, variable-bandwidth amplifier minimizes noise and side-lobe detection in sonar applications. However the distance necessary for proper reading limits the potential of this sensor.
The module has an accurate ceramic-resonator-controlled 420-kHz time-base generator. An output based on the 420-kilohertz time base is provided for external use. The sonar transmit output is 16 cycles ata frequency of 49.4 kilohertz. The 6500 Series module operates over a supply range of 4.5 volts to 6.8 volts, ( 5V is optimal) and is characterized for operation from 0° C to 40° C.
The following is the procedural application needed for proper use:
There are two basic modes of operation for the 6500 Series Sonar ranging module: single-echo mode and multiple-echo mode. The application of power (VCC), the activation of the Initiate (INIT) input, and the resulting transmit output, and the use of the Blanking Inhibit (BINH) input are basically the same for either mode of operation. After applying power (VCC) a minimum of 5 milliseconds must elapse before the INIT input can be taken high. During this time, all internal circuitry is reset and the internal oscillator stabilizes. When INIT is taken high, drive to the Transducer XDCR output occurs. Sixteen pulses at 49.4 kilohertz with 400-volt amplitude will excite the transducer as transmission occurs. At the end of the 16 transmit pulses, a dc bias of 200 volts will remain on the transducer as recommended for optimum operation. In order to eliminate ringing of the transducer from being detected as a return signal, teh Recieve (REC) input of the ranging control IC Is inhibited by internal blanking for 2.38 milliseconds after the initiate signal. If a reduced blanking time is desired, then the BINH input can be taken high to end the blanking of the Recieve input anytime prior to internal blanking. This may be desirable to detect objects closer than 1.33 feet corresponding to 2.38 milliseconds and may be done if transducer damping is sufficient so that ringing is not detected as a return signal. In the single-echo mode of operation (Figure 1), all that must be done next is to wait for the return of the transmitted signal, traveling at approximately 0.9 milliseconds per foot out and back. The returning signal is amplified and appears as a high-logic-level echo output. The time between INIT going high and the Echo (ECHO) output going high is proportional to the distance of the target from the transducer. If desired, the cycle can now be repeated by returning INIT to a low logic level and then taking it high when the next transmission is desired.
If there is more than one target and multiple echos will be detected from a single transmission, then the cycle is slightly different (Figure 2). After receiving the first return signal which causes the ECHO output to go high, the Blanking (BLNK) input must be taken high then back low to reset the ECHO output for the next return signal. The blanking signal must be at least 0.44 milliseconds in duration to account for all 16 returning pulses from the first target and allow for internal delay times. This corresponds to the two targets being at least 3 inches apart.