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uSwitch - a hydroacoustic remote control system
Data brief

uSwitch - A hydroacoustic remote control system
Data brief

0. Motivation

We develop a wide range of professional hydroacoustic communication and navigation equipment using the most advanced technologies in our field. Such equipment is very difficult (and very expensive!) to develop and test, which naturally affects its availability to a wide range of consumers. At the same time, we believe that the availability of technology, especially for new generations of researchers and engineers, is extremely important. That is why we are moving towards the popularization of hydroacoustics, and we hope that uSwitch will become one of those projects that will allow a large number of enthusiasts and fans to dive into the world of underwater communications. After all, most of the world’s oceans have not yet been explored!

1. Operating principle

uSwitch TX and uSwitch RX are two small printed circuit boards (modules): transmitter and receiver. With the help of them, you can transmit up to 4 different control signals through the water column, at a distance of up to 300 meters.

Working with the modules is extremely simple: just connect the hydroacoustic antennas and turn on the power. Each of the modules has pins STROBE, BIT 0, BIT 1 and BIT 2. In the transmitter these are digital inputs, and in the receiver they are digital outputs. By default, all of these pins on both the receiver and transmitter are set to digital one (3.3 Volts).

The transmitted code is formed by the state of the contacts (pins) BIT 0 and BIT 1 , and the transfer occurs when the state of the pin STROBE changes from the state of a digital one to the state of digital zero.

On the receiving side, the received code causes a change in pins BIT 0 and BIT 1, and the fact of reception - by the transition of pin STROBE to the state of digital zero.

Since there are three information pins (BIT 0, BIT 1) and each can have two digital states, 8 different codes can be transmitted in total.

This architecture allows using the uSwitch modules both with various platforms like Arduino, and with simple elements such as buttons, LEDs, relays and others, controlled by TTL levels.

2. Using modules

Figures 1 and 2 show the connection diagrams.

Both modules are powered from a DC source with a voltage of 5 to 15 volts, which allows using both PC USB port, Power bank, lead-acid 12-volt batteries, assemblies based on Li-Ion batteries and usual 9-V “transistor” type batteries to power the modules.

The hydroacoustic transmitting antenna is connected to the OUT and GND pads located on the right side of the transmitter module PCB.

Fig. 1 - uSwitch TX wiring diagram

The hydroacoustic receiving antenna is connected to the IN and GND pads located on the right side of the receiver module PCB.

Fig. 2 - uSwitch RX wiring diagram

On both modules, the same pins are used for interfacing with external devices, on the transmitter these are digital inputs pulled to one, and on the receiver, they are digital outputs with an open collector. The active state of the transmitter inputs is digital zero. For ease of connection, the bottom of the connector is connected to the ground.

To transmit one of the four codes, using pins 3 and 5 (BIT 0 and BIT 1, respectively) the transmitted code is formed. The correspondence of the code number and the state of the pins is shown in table 1.

When the code is received by the receiver module, it, using pins 3 and 5 (BIT 0 and BIT 1, respectively) forms the received code and translates pin 1 (STROBE) to digital zero for 100 milliseconds. Thus, the system connected to it should read the state of pins 3 and 5 after the transition of pin 1 to the state of digital zero.

Table 1 - Correspondence of the state of pins and transmitted/received codes

BIT 0 (pin 3) BIT 1 (pin 5) Transmitted code
0 0 0
1 0 1
0 1 2
1 1 3

After the formation of the transmitted code, for its transmission via the hydroacoustic channel, pin 1 (STROBE) must be set to digital zero for a time of at least 100 milliseconds. The retransmission can be performed no earlier than 500 milliseconds after the beginning of the previous one.

The timing diagram of interaction with modules is shown in Figure 3:

tx/rx time chart
FIg. 3 - The timing diagram of interaction with modules

3. Hydroacoustic antennas

The transmitter module is designed to work with the antenna RT-1.332820-1, and to the receiver module you can connect almost any piezoceramic hydroacoustic antenna, for example, an inexpensive RT-1.d23h03-1 based on a disk piezoelectric element. If you wish, you can make it yourself using our instructions.

4. Limitations

4.1. Limitations from the side of sound propagation in water

The hydroacoustic communication channel is one of the most difficult to transmit information, therefore, the following conditions must be borne in mind for the operation of any hydroacoustic communication system:

4.2. Architecture limitations

We tried to make the most affordable and most functional devices, in some ways we had to compromise. Because different codes are transmitted by sequentially transmitted tone bursts, then the reliability of the codes is not the same and decreases with increasing code. If you need to use less than four codes, then you should give preference to lower codes.

5. Warning

Piezoceramic hydroacoustic antennas are designed in such a way that the pressure they develop strongly depends on the voltage applied to them, therefore, a life-threatening high voltage arises in the transmitter module at the time of signal emission, the amplitude of which reaches 200 volts. Take all required protective measures: while the transmitter is operating, never touch the board and the hydroacoustic antenna connection with your hands or any other parts of your body !!!

6. FAQ

Q: Is there a limit on the number of receivers working with one transmitter?
A: There are no such restrictions: all devices operate in a common frequency band. Any number of receivers will receive the signal from the transmitter, provided that it reaches them. However, given the speed of sound in water (about 1500 m/s), this can happen at different times, with a delay proportional to the range.

Q: Is it possible to work on one reservoir with several sets of the system?
A: It should be borne in mind that all devices operate in a common range and any receiver will respond to any transmitter if the signal reaches it. The user will have to independently ensure the separation of signals in time.

Q: Can the receiver distinguish between signals from different transmitters?
A: No. This option is not provided.

Q: Why is there such a difference in ranges when using antennas RT-1.332820-1 and RT-1.d23h03 -1 as transmitters, 300 meters versus 40?
A: In simple terms, the transmission range is determined by the sensitivity of the receiver and the pressure developed by the transmitting antenna. A flat and inexpensive antenna does not allow the required power to be pumped into it.

Q: Can the transmitter module be powered by batteries??
A: Yes, 9V “transistor” type battery is OK, but since it is only 9V (not 15) you probably will not achieve the maximum range (300 m)

Q: Can acoustic or electromagnetic noise affect the performance of the system?
A: Yes. The receiver is most vulnerable in this sense. The most unfavourable noise is in the working band - 20-30 kHz.

Q: My task requires a larger number of control signals and a longer range, is it possible to somehow modify the system? A: The system was conceived as a hobbyist, and the current performance is actually the limit for the platform used. If you need a larger number of control messages and/or the transfer of arbitrary data, greater range and reliability, then we recommend paying attention to our micromodems uWAVE

Q: I need acknowledgement that the command I send is received by a remote system, how can this be provided? A: The easiest way to use two pairs of receiver-transmitter is to connect both pairs pin to pin (pins 1,3,5).