K02 JSN-SR04T integrated ultrasonic distance measuring module, reversing radar waterproof ultrasonic

The module has two basic modes of operation.

Ping mode works the same basic way as the HC-SR04, HY-SRF05, US-100 and other ultrasonic modules.  The main difference is that the JSN-SR04T requires a longer 20uS TRIG pulse for stable readings.  It also can run Ping mode in an automatic mode of operation where it is automatically triggered every 200mS.

The way Ping mode works is as follows:

1. The module is normally idle.
2. A 20 uSec or wider pulse is sent to the TRIG pin on the module, usually by a microcontroller.  This will cause the module to start a detection cycle.
3. The module emits eight bursts of 40KHz sound and sets it’s ECHO pin output HIGH.
4. When the signal is reflected back from an object and is detected by the module, the ECHO pin is set back to LOW.
5. By measuring the amount of time that the ECHO pin is held HIGH, the distance to the object can be calculated using the basic formula  (Time that ECHO is held HIGH * Speed of sound / 2)  The divide by 2 is because the sound has to travel in both directions (both out and back) and we want to know just the out distance.

Serial mode operates at 9600 baud and works similar to serial mode on the US-100 module.  The main difference is that it also returns a start byte and checksum byte.  It also can be operated in an automatic mode of operation where the module is automatically triggered every 100mS.

The way Serial mode works is as follows:

1. The module is normally idle.
2. A command bye of 0x55 on the RX pin initiates a detection cycle.
3. The module responds with 4 bytes of information
   1. Start bye of 0xFF
   2. Most Significant Byte (MSB)
   3. Least Significant Byte (LSB)
   4. Checksum Byte

The returned value can be calculated using the formula (MSB * 256) + LSB.

The checksum byte is calculated using 0xFF + MSB + LSB.  It returns the least significant byte of the calculation only.

Operating Modes

The module can operate in 6 different modes of operation using either the Ping or Serial mode of operation. These are set by shorting the M1 or M2 pads or placing a resistor of a certain value across the MODE pads.  The resistor value sets an analog voltage that is read by an ADC, so the exact value isn’t overly critical.

Mode 0 and Mode 2 are the most commonly used modes.

MODE 0: Ping Mode

Mode 0 is the default mode when there is no resistor on the MODE pads and neither M1 or M2 pads are shorted and is how the module is shipped.

In this mode, the module operates very similarly to the HC-SR04 and similar ultrasonic range finder modules and sample code for those modules can be used with this module with one exception. With the HC-SR04, the trigger pin is held high for 10uS. With the JSN-SR04T, the trigger pin must be held high longer – usually about 20uS for reliable operation.  The first test program below uses this mode.

MODE 1: Automatic Serial Mode

To enter Mode 1, the M1 pads are shorted OR a resistor value of 47K is placed across the MODE pads.

In this mode the module continuously takes measurements approximately every 100mS and outputs the distance on the TX pin at 9600 baud where it can be read using a serial RX pin on an MCU.

MODE 2: MCU Controlled Serial Mode

To enter Mode 2, the M2 pads are shorted OR a resistor value of 120K is placed across the MODE pads.

This mode is the same as Mode 1 except that the module takes a measurement only when a trigger command of 0x55 is sent to the RX pin on the module. The module then takes a single measurement and outputs the distance on its TX pin.

The minimum trigger cycle time is 60mS

MODE 3: Automatic Ping mode

To enter Mode 3, a resistor value of 200K is placed across the MODE pads.

Mode 3 is similar to Mode 0 (ping mode) except that it automatically generates the ping every 200mS and outputs a pulse width high level corresponding to the distance.

MODE 4: Low power Ping mode.

To enter Mode 4, a resistor value of 360K is placed across the MODE pads.

This mode is the same as Mode 0 except that the module is set to low power in between Pings with a stated current consumption of < 70uA.

MODE 5: Threshold Switch Output

To enter Mode 5, a resistor value of 470K is placed across the MODE pads.

In this mode, the module automatically takes a reading every 200mS and checks the measurement against a factory default threshold setting of 1.5 meters. If the detected distance is less than 1.5 meters, the Echo pin is set to HIGH. If the detected distance is greater than 1.5m, the Echo pin is set to LOW.  This can be handy for using the output to directly control something like a relay or LED.