SensComp 6500 Ranging Module

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More Details:

Accurate Sonar Ranging from 6 inches to 35 feet

Drives 50-kHz Electrostatic Transducer with No Additional Interface

Operates from Single Supply

Accurate Clock Output Provided for External Use

Selective Echo Exclusion

TTL-Compatible

Multiple Measurement Capability

Uses TI TL851 and Polaroid 614906 Sonar Ranging Integrated Circuits

Socketed Digital Chip

Convenient Terminal Connector

Variable Gain Control Potentiometer

The 6500 Series is an economical sonar ranging module that can drive all SensComp/Polaroid electrostatic transducers with no additional interface. This module, with a simple interface, is able to measure distances from 6 inches to 35 feet. The typical 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. The digitally controlled-gain, variable-bandwidth amplifier minimizes noise and side-lobe detection in sonar applications.

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 and is characterized for operation from 0° C to 40° C.

6500 Board Schematic

Absolute Maximum Ratings

Voltage from any pin to ground (see Note 1)	7 V
Voltage from any pin except XDCR (see Note 1) to V_CC	-7 to 0.5 V
Operating free-air tempurature range	0° C to 40° C
Storage temperature range	-40° C to 85° C

Recommended Operating Conditions

		Min.	Max.	Unit
Supply voltage, V_CC		4.5	6.8	V
High-level input voltage, V_IH	BLNK, BINH, INIT	2.1		V
Low-level input voltage, V_IL	BLNK, BINH, INIT		0.6	V
ECHO and OSC output voltage			6.8	V
Delay time, power up to INIT high			5	ms
Recycle period			80	ms
Operating free-air tempurature, T_A		0	40	° C

Electrical Characteristics Over Recommended Ranges of Supply Voltage and Operating Free-Air Tempurature (unless otherwise noted)

Parameter		Test Conditions	Typ.	Max.	Unit
Input current	BLNK, BINH, INIT	V_I = 2.1 V		1	mA
High-level ouput current, I_OH	ECHO, OSC	V_OH = 5.5 V		100	uA
Low-level output voltage, V_OL	ECHO, OSC	I_OL = 1.6 mA		0.4	V
Transducer bias voltage		T_A = 25° C	200		V
Transducer output voltage (peak to peak)		T_A = 25° C	400		V
Number of cycles for XDCR output to reach 400 V		C = 500 pF		7
Internal blanking interval			2.38*		ms
Frequency during 16-pulse transmit period	OSC output XMIT output		49.4* 49.4*		kHz
Frequency after 16-pulse transmit period	OSC output XMIT output		93.3* 0		kHz
Supply Current, I_CC	During transmit period After transmit period			2000 100	mA

* These typical values apply for a 420-kHz ceramic resonator.

Specifications subject to change without notice

Operation With SensComp Electrostatic Transducer

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 (V_CC), 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 (V_CC) 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.

Figure 1 - Example of Single-Echo-Mode Cycle without Blanking Input

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.

Figure 2 - Example of Multiple-Echo-Mode Cycle with Blanking Input

Information reprinted with permission from SensComp/Polaroid. Thanks SensComp/Polaroid!

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