Ultrasonic Positioning 

The Ultrasonic Positioning System HX900 is a system of devices used for either tracking or guidance, or a combination of both. The components of the HX900 are the Hexamite Positioning Devices featured below.  These devices harness ultrasound for high resolution, high repeatability positioning. The smallest system conceivable consists of at least two Hexamite Positioning Devices where one device knows the distance to another. The Hexamite positioning devices are referred to as either Beacons (transmitters) or Pilots (receivers). Each Hexamite Pilot knows its distance to every Hexamite Beacon in range, with sub-millimeter resolution. Any Hexamite Positioning Device can be configured either as a Pilot or a Beacon; setup strings govern the operation of the devices. Your “Positioning System” may consist of an indefinite number of Hexamite Positioning Devices, configured as Pilots and Beacons, to form a large multi-point, multi-dimensional system that suits your needs.

HX900 Ultrasonic Positioning Device

Hexamite Positioning Device (HPD) HX900 is suited for tracking and guidance application. It has a built in 40KHz sensor and a high power output, which gives it an extra range. Low power options are available for battery operations. Indefinite number of HX900 devices can be connected together using multidrop RS485 networks, and spread over large areas for tracking or guidance operations. Direct RS232 via serial cable is also available for smaller systems. See PDF catalog for more information.

HX944 Ultrasonic Positioning Device

Hexamite Positioning Device HX944 has 4 transmission channels and 4 receive channels, this device can report the distance from any number of beacons to 4 differently positioned sensors. This device is ideal for a single moving object guidance, it facilitates broader angle operation and can also provide object orientation data.

Important: The positioning devices are sensitive. While connected to a computer some ungrounded switching power supplies from laptops and desktops can disturb the positioning devices. In case of trouble, make sure all computers or terminals connected to the devices are well grounded. Laptops and terminals running on batteries do not disturb the devices while connected.

Multipoint Multidimensional System

The illustration on the below is an example of a 6 point system, using 6 Hexamite Positioning Devices. There is no fixed limit for the size of the system in terms of points. Point 1, 2, 3 and 4 are shown as fixed points in the corner of the enclosed area on the right, 5 and 6 may be thought of as moving points. Or points 5 and 6 can be stationary and the perimeter moving in relation to the two, any setup is possible. Any point in the system can be configured as either pilot or beacon. The system can be setup within perimeters or in open spaces. Hexamite Positioning Devices operate in the ultrasound range around 40Khz with range to about 16m (absolute maximum) per point in the system (other frequencies and ranges are available). Number of devices can be setup within the space monitored, to increase the overall range.

The Hexamite Ultrasonic Positioning System is  synchronized. Synchronization is achieved by connecting the devices together or by remote means such as radio, light or sound. Hexamite Positioning Devices allow synchronization via serial input (RS485/RS232) or by sound (ultrasound). In the case of a tracking system where point 1, 2, 3 and 4 are fixed pilots and points 5 and 6 are moving beacons. It is proper to connect point 1, 2, 3 and 4 together via RS485, and utilize one or all of the fixed devices to synchronize 5 and 6 with the built in sonic synchronization feature. 

A guidance system consisting of a single pilot where the pilot synchronizes the beacons using ultrasound is easily accomplished. The situation gets more complex if 5 and 6 are set up as pilots guided by 1, 2, 3 and 4 set up as beacons. This is particularly true if the pilots are not connected together. If pilot 5 is used to synchronize the beacons using the built in sonic synchronization feature, then pilot 6 doesn't know when the timing cycle starts. If there is only one pilot being guided by the beacons, sonic synchronization is not a problem. In the case of multiple mobile pilots guided by a system of beacons, it is necessary to use other means of synchronization. 

Any pilot can be configured as the master, the master initiates timing or distance acquisition cycle of the whole system by transmitting a synchronization signal at the beginning of the cycle. At the end of the cycle, all the pilots transmit their positioning data one after another over the serial network. See Application Examples for more details. 

Software Configuration

The device can be configured through it's serial port. It will accept a string of bytes which effect the behavior of the device. These bytes are stored first in the work registers of the device and used for following operation. If the checksum matches the string, the configuration data is stored in the permanent nonvolatile memory. Once the string has been secured in permanent memory, the device will acknowledge by transmitting the ASCII character + via it’s serial port

The setup data is stored on EEPROM and will not be erased if the device is turned off. On startup the setup string in the EEPROM is loaded into work registers and used by the program 

Device Addresses

 Each device has two addresses i.e. a primary and a secondary address. The response of the device depends on the first byte in the string it receives. If the first byte is the primary address of the device, it responds by transmitting the data acquired during last acquisition.

 The secondary address must always precede the setup string.

Configuration Data Interpretation

The first byte in the configuration string is the secondary address of the device. The second byte dictates the operation (Mode) of the device. The third byte determines how the device interacts with other devices in the group. Following is a list of the bytes and corresponding functions.

Configuration String 

The user can effect the operation of the device and control the configuration of the network, by downloading  the configuration data onto the network or radio link. This can be done via the serial port of any personal computer. Ordinary terminal program like "Microsoft Terminal" can be used for this operation. The setup data is stored on EEPROM and will not be erased if the Positioning Device is turned off. On startup the setup string in the EEPROM is loaded into work registers and used by the program. If the ESC character is transmitted on the network, the program control byte PCB in the work register of all devices on the network is cleared. If the ESC character is used the system must be either restarted or strings re-entered to resume normal operation. 

Program Control Byte

Program control byte allows the mode of operation to be altered externally (over the RS485/RS232 or Radio link). This is done by clearing or setting the bits of the byte. Bit 7 is the mode control bit, it sets the device as either Beacon or a Pilot. If bit 7 is high the device is a beacon, if this bit is low the device is a pilot.

Bit 1 Synchronization Override

The first beacon to start the emission sequence, sinks it’s synchronization I/O low. Beacons linked using the synchronization I/O are all synchronized to the first beacon to start the emission sequence.

Bit.2: Serial Network

This bit should be set if the beacons are serially linked to the pilot network. If this bit is cleared, the beacon will ignore all serial data on it’s serial input except the ESC character.

When the device is configured as a pilot, it idles (waiting for serial input). If the primary address of the device is entered via the serial port input while it idles, the device responds by transmitting the results of it's last position acquisition cycle. If hyphen "-" (synchronization) is entered via the serial port input, the device immediately enters position acquisition cycle. If bit 3 is set the device will enter position acquisition cycle and submit the results through it's serial port. If bit 1 of the Program Control Byte is set the device will wait for a falling edge on it's I/O synchronization pin before commencing with the position acquisition cycle.

Bit.0: If set the pilot is set up for sonic synchronization mode, if transmission is enabled the pilot transmits the sonic synchronization signal.

Bit.3: If set the pilot continuously cycles through its program and transmitting the results over the serial lines. This bit is useful when there is only a single pilot or the pilot is the only pilot in operation on the network.

Bit.4: If set the pilot initiates the distance acquisition cycle once it receives a carriage return on the network. The pilot with this bit set is the master on the network. It transmits the GO (ASCII eq. 45 decimal) signal (valid for both pilots and beacons) to the rest of the devices when it receives a carriage return. It also sinks the synchronization I/O to low momentarily just after GO has been transmitted.

General

Bit.0 is most often identical for both pilots and beacons, with in operating range. This bit sets these devices up for sonic synchronization. During sonic synchronization the pilot must be given an extra field. In other words if you have beacons designated as 1 and 2 if the sonic bit is set the number of beacon byte must be one larger than the number of pilots or NBB=BDB(max)+1 (see Device Control Bytes).

NSB Noise Suppression Byte

The noise suppressor, can be set from 00 to 18 (hex). The higher this number the harder it is to upset the measurement. At 00 no noise suppression is applied, at 18 hex the 10m range is compromised. The noise suppression is achieved at the expense of the range. Low numbers may not have any significant effect on the range. At 06 minor explosions (firecrackers) will have little effect.

Termination Byte (TB)

This byte serves as the string termination byte and it is also used to propel a network of chained devices. This byte can be used to force other devices to transmit their results.

If the termination byte of device 'X' is the primary address of device 'Y' on the same network, then final byte in the result string from device X forces device Y to transmit it’s result string. See Master (Chain Initiator) section.

sector

Number of Beacons Byte (NBB)

This number determines how many Beacons the pilot looks for during the position acquisition cycle, it describes the system to the positioning device. All pilots and beacons in the system must contain the same value for the Number of Beacons Byte. The pilot will submit via it's serial port 1+NBB number of 16 bit position data segments. The size of the data segment depends on the number of channels the pilot has. It is proper to refer to these segments as Beacon Segments. There is an extra segment that cannot be referred to as beacon segment, Synchronization Segment would be more appropriate. The information in the synchronization segment relates to the pilot itself. This segment can be used to establish current speed of sound for compensation and more (see application notes).

Beacon Designation Byte (BDB)

The Beacon Designation Byte applies only to beacons, the pilot ignores this number. The value of this byte determines the designation of the beacon. The BDB must have a value less than or equal to the NBB. For example in the case of a 4 (BDB=3) point system, where three devices are configured as beacons and one device configured as a pilot. If the Number of Beacons Byte for all devices has the value three AND each Beacon has been given a different BDB value for example 1, 2 and 3.  Then the Pilot will submit a data string similar to the following through it's serial port.

0000 1A22 3334 14FF

This means that there are (1A22)=6690 millimeters from the pilot to the device with BDB equal to 1, and (3334)=13108 millimeters to the device designated 2 and (14FF)=5375 millimeters to the beacon designated 3. Note that the Synchronization Segment is 0000, it is always the first segment serially transmitted.

Using the same four point system we can set it up as two pilots and two beacons. We can set the BDB of the system equal to two, so both pilots look for two beacons. We can set one pilot up as master (active device) and another as slave, then by typing the ASCII character 13 carriage return onto the network of the two pilots, the system will submit the following string.

0833 2566 1FFF z2131 211B 1200

The above assumes the slave pilot has a primary address equal to the ASCII character z. It is stated here that there are (2566)=9574 millimeters form the master pilot to beacon one, and (1FFF)=8191 mm from the master pilot to beacon two. There are (211B)=8475 mm from slave pilot z to beacon one and (1200)=4608 mm from slave pilot z to beacon two. Since the Master Pilot was set up to transmit the sonic synchronization, there are (833)=2099 mm from the master to the nearest obstacle, and (2131)=8497 mm from pilot slave z to the master. 

Conversion example (converting a hexadecimal number to decimal)

211B = (2 x 16 x 16 x 16) + (1 x 16 x 16) + (1 x 16) + 11 = 8475 note that B = 11

Communication Protocol

Each device has a primary address and a secondary address. The secondary address is always the primary address + 1, the primary address is always an even number, and the secondary address is always an odd number. All broadcasted bytes are hexadecimal characters (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F). Addresses and commands received by the device are binary (0-255). Addresses are in the range from 71 to 255, and 3 command (control characters) are used. Characters are ignored unless these directly apply, like ' carriage return ' (13), the character ' - ' (45), the character 'esc' (27) and own addresses. The character ' - ' ( 45) is interpreted by the devices on the network as a synchronization signal, this signal will plunge the devices into action as dictated by the set up.

If the ESC character is transmitted on the network the Device Mode Control byte in the work register is cleared. This applies for all the devices on the network. 

 Idle (normal operation)

 The device idles when there is no acquisition or entry in process. In idle mode it is alert to data received via the serial port, it also monitors the synchronization input. In this mode it responds to through serial input: a hyphen ‘-‘, primary address, secondary address and carriage return (if set up as master). A low on the synchronization input will plunge the device into acquisition. The ESC character will break any operation and force the device into idle mode.

The Primary Address

When a device receives it’s primary address over the serial port, it submits the results of it’s last acquisition, by transmitting these via the serial port.

The Secondary Address

When the device receives it’s secondary address, it will enter the following valid hex bytes into work registers until it receives a carriage return. Once a carriage return is received the device proceeds with normal operation. During entry only the hex characters 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F and carriage return are valid, all other characters are ignored. If the characters FF plus a carriage return are entered following the primary address, the device transmits the contents of the work registers over the serial port.

If a full string is entered into all the work registers, and this string is followed by a correct check sum (that is the sum of all bytes entered excluding the primary address), the device will store this string in EEPROM or permanent nonvolatile memory. This string will be loaded into the work registers whenever the device is restarted.

Once the string has been secured in permanent memory the device will acknowledge by transmitting the ASCII character + via it’s serial port.

Master (Chain Initiator)

A device which is set up as the master, will transmit a synchronization (hyphen ‘-‘) onto the serial network. This will force a synchronized acquisition for all the devices on the network. The Master also sinks the synchronization output low for the duration of the sonic signal transmission. The Master is forced into action if it receives a carriage return over the serial port. This feature is useful for closing the chain loop and maintaining continuous operation.

IF (the last device in a chain of network devices has a “serial output termination” byte equal to 'Carriage return') AND (one device on the network has been set up as the master) THEN the acquisition cycle is repeated indefinitely with a very high sampling integrity.

Note that it is not imperative that one device be set up as a master, the operation can be propelled by a PC.

There can only be one master at a time on the same network

Output Format

The output format depends on the way the devices have been set up and the size of the positioning system. For a system with 2 single channel pilots and 1 four channel pilot chained together, depending on the setup the output may be as follows:

Assuming the primary addresses of pilot 2 and 3 are R and T respectively. For a two beacon system the string outputted will be similar to the following:

-#### #### #### R#### #### #### #### #### #### #### #### #### #### #### #### T#### #### #### (CR)

#### stands for 16 bit hex value.  

Serial Network Introduction 

There are two network options available for hexamite devices, (with the exception of HX900L and HX900B). These options are RS485 (recommended standard 485) or the hexamite serial I/O.

RS232USB

RS232 ports are disappearing from modern laptops. It is however possible to use the USB port. The photograph on the right shows the RS232USB cable. This cable allows the computer to communicate with all hexamite products through the USB port.

The Serial I/O is low cost single ended and the nature of communications is simplex. Data is both transmitted and received through a single wire (plus return). The serial I/O line must be in the state of high impedance if data is not being transmitted. The longest distance between any two devices on the network should not exceed 20 meters. Maximum number of hexamite devices per Serial I/O line should be less than 175, higher number can be realized up on request. The HX9RS232 serial cable links the Serial I/O to RS232 port on a PC or a terminal.

Serial I/O Network to RS232 

The illustration to the right shows how a number of devices can be connected via HX9RS232 serial cable to a PC. There is a power tap on the HX9RS232 it can be used to provide power to a network of devices. This setup is for a short distance communication no further than 20 meters.

Adding microcontrollers to the serial I/O 

The illustration on the right shows how Microcontroller can be connected to a hexamite serial network (serial I/O). Any Microcontroller can use receive input Rx to monitor the network. If the Microcontroller must to transmit onto the network, the Tx line needs to be in high impedance mode when the Microcontroller is not transmitting. This is readily achieved when using Atmel AVR Microcontrollers. UCR.3. The Tx pin should be set up as input using the data direction registers. The serial transmission should be turned on only during transmission by setting And turned off after transmission by clearing UCR.3. The same can be achieved with the Microchip PIC by setting and clearing the TXEN bit.

The RS485 is designed for long distance multidrop communications on lines many kilometers in length. Up to 128 hexamite devices can be applied per network. If communications is needed for more devices, a repeater or repeaters should be added and used.

RS485 network to RS232 

The illustration on the right shows how a network of devices can be connected using RS485. The RS485 is a long range communications facility which allows kilometers between devices.

Serial I/O to RS485

The illustration to the right shows how a serial I/O network can be linked to a computer via long distance RS485 connection HX485IO and HX9RS485. The output pin on the external microcontroller must go high when the microcontroller transmits data.

Application: Multi-dimensional Guidance System 

The illustration on the right shows a setup for a 4 point guidance system. Here the moving object uses 3 remote beacons to calculate it's own position. The Hexamite Positioning Devices HPD1, 2 and 3 are configured as Beacons. HPD4 on the mobile object A is configured as a pilot, the system is set up as shown in the table below 

(please refer to the software configuration section).

 The Pilot has been set up to emit a sonic synchronization signal, it will synchronize all beacons in range. It will transmit continuously through it's serial port the distances B1-P4, B2-P4 and B3-P4 plus the distance the sonic synchronization signal had to travel. 

 This is twice the actual distance from the pilot to each beacon. If there is more than one beacon using the same Beacon Designation Byte (BDB) within range of the pilot, the pilot will submit the distance to the closest of the identical beacons. This allows a large number of beacons to be set up within and outside the monitored perimeter without sacrificing Position Sampling Rate. The Position Acquisition Time of this 4 point system is 0.528 + 0.0052 seconds.    

The Position Acquisition Time of this 4 point system is 0.528 + 0.0052 seconds.   

Application example 3. Six Point Guidance (Tracking) System

The illustration on the right, shows a 6 point system linked using wireless means. This allows simultaneous guidance and tracking. The setup enables virtually instantaneous synchronization of all Positioning Devices in the system. If the wireless link is sophisticated and will enable data communication, then each Positioning Device can be set up between Position Acquisition cycles. In this case the system is both a guidance system and a tracking system since all positions can be extracted out of all Positioning Devices, i.e. HPD1 can be configured as pilot through the wireless network hence it will be able to report it's position relative to other devices. The wireless link can be realized using light or radio, and positioning data submitted by the pilots is the actual distance + the time it took for the synchronization signal to travel to the Positioning Device (speed of light ). This error is insignificant. Again the Position Sampling Rate is based on the number of beacons in the system. For the illustration on the right as it is set up is 0.66 + 0.008 seconds. 

Application Example: Four Point Tracking System 

The illustration on the right shows a setup for a 4 point tracking system. Here an external computer tracks the position of two remote moving objects. The Hexamite Positioning Devices HPD1 and HPD2 are configured as Pilots. And the Hexamite Positioning Devices HPD3 and HPD4 are configured as Beacons (see software configuration). Assuming HPD1 and HPD2 have primary addresses 7F and 6E respectively. Then the system is set up as shown in the table below.

(please refer to the software configuration section). 

Hexamite Positioning device 1 is set up as master and the sonic synchronizing device. At the end of the acquisition cycle the master transmits the distance P1-B3 and the distance P1-B4 over the RS485 serial line. At the end of the transmission the master calls device with primary address 6E. This will force HPD2 to transmit the distance P2-B3 and P2-B4 followed by a carriage return over the serial line. The carriage return forces HPD1 to initiate another Position Acquisition cycle. The distance data reported by HPD1 is actually twice the distance P1-B3 and P1-B4. It is the distance the sonic synchronization had to travel to reach the beacons plus the distance the response signals travelled from the beacons. Hence the actual distance value submitted by HPD2 is (P1-B3) + (P2-B3) and (P1-B4) + (P2-B4). The position acquisition time of this 4 point system is 0.264 + 0.0078 seconds. 

X in the table means that the device ignores this byte. 

Ultrasonic Guidance System  with Object Orientation Features

The illustration on the right shows a moving vehicle. HX944 set up as pilot is mounted on the vehicle. The two beacons can consist of any Hexamite Positioning device HX900, HE860, HX900B and even another HX944. Any 40khz hexamite sensors can be used as sensor 1, 2, 3 and 4. In the illustration transmitter 1 (t1) and receiver (r1) are setup to face each other. The HX944 will report the distance from transmitter 1 to receiver 1. If this distance is fixed, the speed of sound can be calculated for reference. This set up achieves high absolute position and orientation accuracy in any temperature and humidity conditions. If there is nothing to block line of sight from Receiver 1 to the beacons, Receiver 1 will also pick up the distance (B1-P1) and (B2-P1).  Due to extreme angle between Beacon 1 and P4, this distance is not likely to be reported by the HX944.

Assuming there are no other Hexamite devices in network group operation with the HX944 and further assuming the HX944 has the primary address P then the following string will set the HX944 up for this operation.

 Q 09 0D 03 00 04 00 1D

Device Q is set up as pilot in a 2 point system NBB = Beacons +1=03, the designation byte doesn’t apply, noise suppression=04 (may not be necessary). 29 is the checksum

Assuming beacon 1 has primary address H and beacon 2 has primary address J then

I 81 0D 03 01 00 00 92

K 81 0D 03 02 00 00 93

This will set Hexamite positioning device HPD1 and HPD2 up as beacon 1 and beacon 2 respectively. Once the strings are loaded into the devices with the checksums 92 and 93 the operation will commence automatically.

During the operation the HX944 will continuously transmit the following format:

TxR1 TxR2 TxR3 TxR4 B1P1 B1P2 B1P3 B1P4 B2P1 B2P2 B2P3 B2P4 (CR)

The string is terminated with CR or (0D) as specified in the setup string. The above string is symbolic, the real data is going to look more like

0133 0000 0000 0000 12CD 12C0 1139 0000 3111 4032 4322 2333 (CR)

TxR1 is the distance from Receiver 1 to the nearest detectable transmitter, it doesn’t matter from which transmitter the reference signal is transmitted, the nearest detectable transmitter is the key. The data above is fictional, to indicate what sort of data is read using a serial com terminal program. The object orientation can be calculated from the data. Assuming the line of sight angle is to large for the B1P4, no signal is likely to be picked up hence data will be 0000. The Hx944 will transmit this data continuously until stopped using the (ESC) character.

TxR2, TxR3 and TxR4 could actually contain the distance calculated to the nearest object if no sensor is directly facing the respective receiver. If this is the case this data should be ignored.

Note that in this application example the beacons are fixed and the pilot is moving, the same setup can be used for a situation where the HX944 is stationary tracking the position of the moving beacons.

Economy Guidance Application with Object Orientation

The HX944 can be set up as 4 separate beacons, it will operate with any other Hexamite Ultrasonic Device, the following example shows a setup using two HX944 devices. 

Using HX944 as Beacons

The illustration, shows the HX944 set up as beacons, in this example there are 16 distance values from beacon sensors to pilot sensors. The data transmitted over the serial lines by the HX944 is as follows:

TxR1 TxR2 TxR3 TxR4 B1P1 B1P2 B1P3 B1P4 B2P1 B2P2 B2P3 B2P4 B3P1 B3P2 B3P3 B3P4 B4P1 B4P2 B4P3 B4P4

Wires must connect the sensors to the HX944 beacon. The length of the wires has an effect on the system’s performance. Assuming the primary address of the HX944 shown as beacon in the illustration on the right is R, then the setup string to turn the device into beacons is:

S 81 0D 05 00 00 00 93 … 93 is the checksum

The pilot must be set to fit this system of beacons, assuming the pilot has the primary address T, the set up string can be:

U 09 0D 05 00 00 00 1B … 1B is the checksum

It is possible to add more HX944 units to both the beacon setup and the pilot setup. If one more HX944 is added to the pilot setup and if T is set up as master (see Master (Chain Initiator) section) and the new device has the primary address V. Then if the following strings are submitted the device, a string of  40 distance values will be transmitted over the serial lines.

W 01 0D 05 00 00 00 13 … 13 is the checksum

U 11 56 05 00 00 00 6C … 6C is the checksum

The results are achieved at no cost to sampling rate, before 20 distance values were received per unit time. With the add on unit 40 distance values are received per unit time.

The data for this setup transmitted over the serial lines is similar to the following: 

            TxR1 TxR2 TxR3 TxR4 B1P1 B1P2 B1P3 B1P4 B2P1 B2P2 B2P3 B2P4 B3P1 B3P2 B3P3 B3P4 B4P1 B4P2 B4P3 B4P4 [V] TxR1 TxR2 TxR3 TxR4 B1P1 B1P2 B1P3 B1P4 B2P1 B2P2 B2P3 B2P4 B3P1 B3P2 B3P3 B3P4 B4P1 B4P2 B4P3 B4P4

Or if no signal is detected by any sensor then the following data is transmitted over the serial lines:

– 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 V0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 (CR)

If another beacon is added to beacon S (secondary) for the same system the setup strings would have to be assuming the new device is X (primary):

Y 81 0D 09 00 00 00 97

S 81 0D 09 00 00 00 97

W 01 0D 09 00 00 00 17

U 11 56 09 00 00 00 70

In this case a total of 80 distance data would be received over the serial lines, and here is a cost to the acquisition time since the unit was added to a beacon.

Application Indefinite Guidance along a path

The figures 3g and 3f, illustrate how guidance may occur along a path. Beacons 1 and 2 guide the vehicle initially. The Pilot always locks on the signal arriving first, and it ignores signals arriving later.  Even if beacon 3 or 4 is picked up in the initial position, these signals are ignored. Since line of sight is required for positioning. Once beacon 1 and 2 are passed, the Pilot on the vehicle no longer receives signals from Beacon 1 and 2. Both position and orientation can be calculated anywhere on the path, beacons can be placed a very long path in this manner and guide the vehicle. 

 

Figure 3g

Once the vehicle passes beacons 1 and 2, beacons 3 and 4 take over the guidance.  Two HX900L or HE900 placed on the front corner of the vehicle, and connected together by the synchronization wire will be sufficient to report both position and orientation. 

 

Figure 3f

HX944 Application Consideration

The synchronization segment is the only segment a pilot displays when a device is configured as follows: 

Q 09 0D 00 xx xx xx

or

Q 11 0D 00 xx xx xx

or

Q 01 0D 00 xx xx xx

[(xx) means: don’t care]

If a 4 channel device like the HX944 is in an environment settings like shown in Fig. 3c. The Q 09 string setup will transmit the following data form over the serial lines. 

T1R1 T1R2 T1R3 T1R4 (CR) 

The HE944 responds to the first signal it receives, and outputs a value proportional to the distance to it. It doesn’t matter where the signal came from, from a beacon or an echo of an object. The HX900 series base their operation partially on the fact that echoes always arrive behind the direct line of sight signal. T1R2, T1R3 and T1R4 will all hold the line of sight distance to the transmitter. Receiver 1 is not in the line of sight and T1R1 will hold a value proportional to the distance from the transmitter to the echo object plus the distance from the object to receiver1. 

The Q 11 and Q 01 setups will yield similar results, but these setups include other  chained devices in the result string as well. 

Connecting Sensors to Channels

Figure 3d shows the types of connections to a transmission channel and a receive channel. For a receiver, a shield is required. It is possible to serial connect more receivers on a single receive channel to obtain a higher level of omni-directionality. Two receivers joined back to back and serially connected to a receive channel will enable reception front and aft. Same goes for the transmission channel, transmission front and aft can be achieved similarly. Multiple transmitters on a single channel should be parallel connected. Transceivers are equally good for reception and transmission and can replace transmitters and receivers where needed. It should be noted that there is a load condition cost for multiple sensors per channel, and the number of sensors used is at the user’s discretion.

Small Room Syndrome

When there direct line of sight is poor (i.e. the angle q becomes critically small) or none existent, the direct line of sight signal may become so weak that it isn't registered. In this case echoes from walls may cause problems particularly if the enclosed perimeter is much smaller than the maximum range of the system. As seen in the figure on the right  the distance l1 may be substituted by the distance l2 + l3 if the angle becomes very small. The critical angle depends on the distance from the sensor source S. The closer the pickup B is to the source the smaller is the critical angle. In case of A there is no line of sight, therefore the distance measured may become d1 + d2 depending on the size of the confine. Close to the sensor S the critical angle is only a few degrees, but out at the range limit the angle is about 90 +/- 20 degrees. 

Distance Calculations

When a sonic synchronization is used between remote devices, the time of flight of the synchronization signal must be taken into account.

 Figure 3a shows a transmitter and a receiver located at a distance from  HPD beacon. The Transmitter synchronizes the beacon, the total distance calculated by the HPD pilots is therefore TX>>HPD + HPD>>RX. In case many transmitters are used to synchronize the beacons the transmitter closest to the beacon always synchronizes the beacon.  In order to determine which transmitter synchronized the beacons, either transceivers should be used or the transmitters should be located close to the receivers.   

In figure 3b on the right all the transceivers are used to transmit the synchronization signal. To determine the actual distance to each transceiver,  must find the lowest value in the data string. Once the lowest value obviously HPD<>TC3 is determined, then the distance

HPD<>TC3 = 0.5 * HPD<>TC3.

When the shortest distance is known, the rest of the distances can be determined. 

HPD>>TC1=HPD>>TC1 - 0.5 * HPD<>TC3

and

HPD>>TC2=HPD>>TC2 – 0.5 * HPD<>TC3

It is advantageous to have all transceivers attempt to synchronize the remote beacon. If synchronization doesn’t take place no distance is measured. If only one transceiver is used then it may or may not be close to the beacon and may or may not activate the beacon.

The distance data from the HPD represents the time of flight of the signals, the timer timing the signals increments every 2 microseconds. Increments are 500000 per second. The sound travels fixed meters per second or about 344m/s @ 25 degrees C.  The equation for calculating distance is:

Distance = K + (C * Increments) / N

Where

C = Speed of Sound

N = Increments per Second

K = calibration correction (increases by fraction of a millimeter per meter)

The increment data from the HPD is presented in hexadecimal, assuming the distance data HPD>>TC3 = 1C88 this can be converted to decimal as follows:

Increments (HPD>>TC3) = 1x16³ + Cx16² + 8x16 + 8 = 4096 + 3072 + 128 + 8 = 7304

Distance = 344 (m/s) x 7304 (increments) / 500000 (increments per second) = 5.025 m