Product Overview

The SR94 waterproof ultrasonic long-range sensing module is designed for distance and level measurement using ultrasonic time-of-flight technology. The module integrates a high-performance processor and high-quality components to ensure stable operation and long service life.
It adopts a fully sealed waterproof ultrasonic transducer, providing strong environmental adaptability. When used with the dedicated horn structure, the sensor supports longer measurement ranges.
The SR94 series offers multiple output modes and is a high-performance, highly reliable commercial-grade sensing module that is easy to operate and integrate.

Product Features

Operating voltage options: 3.3V–5V; RS485 version supports 5V–12V
Output modes:
- UART automatic output
- UART triggered output
- PWM automatic output
- PWM triggered output
- Switch output
- RS485 output
Standby current can be lower than 10µA
Fully sealed waterproof sensor head
Built-in temperature compensation
Operating temperature: –15°C to +60°C
Storage temperature: –25°C to +80°C
Measurement accuracy: ±(1cm + S × 0.3%), where S is the measured distance
Built-in ESD protection on sensor housing and I/O pins, meeting IEC61000-4-2 requirements

Product Advantages

High protection level
Strong anti-interference capability
Stable and reliable output data
Low power consumption
High ESD resistance
High measurement accuracy
Compact size and easy installation
Automatic output mode reduces workload on the host processor
Trigger-controlled mode enables optimized low-power operation

Application Fields

Horizontal distance measurement
Water level and liquid level monitoring
Parking systems
Object detection and presence sensing
Smart waste bin level monitoring
Robotics obstacle avoidance and automation control
Sewer and well water-level monitoring

Basic Specifications

(SR94 values derived from the original flat-surface measurement model)

Parameter	Value	Unit	Notes
Operating Voltage	3.3–5V (RS485: 5–12V)	V	—
Average Current	<10	mA	Typical at 5V, 100ms cycle
Blind Zone	≤28	cm	—
Range (without horn)	28–450	cm	Flat surface measurement
Range (with horn)	28–750	cm	Extended range
Beam Angle (without horn)	≈75°	—	Reference value
Beam Angle (with horn)	≈40°	—	Reference value
Output Methods	UART Auto / UART Triggered / PWM Auto / PWM Triggered / Switch Output / RS485	—	—

Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	RX	Function pin (depends on output mode)
4	TX	Function pin (depends on output mode)

The functionality of RX and TX depends strictly on the selected output mode and cannot be mixed.

Mechanical Characteristics

The SR94 module is available in two physical configurations:

1. Without Horn (Standard Version)

Compact and fully sealed ultrasonic transducer
Suitable for medium-range measurement applications

2. With Horn (Long-Range Version)

Extended acoustic structure improves sensitivity and increases maximum range
Optimized for long-distance flat-surface and liquid-level measurement

Output Methods

The SR94 supports multiple output modes. Each output mode has specific electrical behavior, timing characteristics, and communication formats. The following sections describe each mode in detail.

1. UART Automatic Output Mode

1.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	RX	Selection pin for processed or real-time values
4	TX	UART output pin

RX pin determines the output data type at power-up.
Pin functions cannot be mixed with other output modes.

1.2 UART Automatic Output Behavior

When RX is floating or at high level → the module outputs processed values, which are more stable (response time: 300–500 ms).
When RX is low level at power-up → the module outputs real-time values (response time: 100 ms).

Note: The RX pin is checked only at power-up when selecting between processed and real-time values.

1.3 UART Communication Parameters

Logic level: TTL
Data bits: 8
Stop bit: 1
Parity: None
Baud rate: 9600 bps

1.4 UART Data Frame Format

Byte	Description
0	Frame Header (0xFF)
1	Data_H (distance high byte)
2	Data_L (distance low byte)
3	Checksum (SUM)

Checksum:
SUM = (FrameHeader + Data_H + Data_L) & 0x00FF

Distance Calculation:
Distance = Data_H × 256 + Data_L (unit: mm)

1.5 UART Output Example

Frame Header	Data_H	Data_L	SUM
0xFF	0x07	0xA1	0xA7

Checksum example:
SUM = (0xFF + 0x07 + 0xA1) & 0xFF = 0xA7
Distance = 0x07A1 = 1953 mm.

2. UART Triggered Output Mode

2.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	RX	Trigger input pin
4	TX	UART output pin

2.2 UART Triggered Measurement Behavior

A falling-edge pulse on RX or any received UART data triggers a measurement.
After measurement, distance data is sent through TX.
Trigger cycle must be ≥ 70 ms for standard measurement.
Response time for SR94 (liquid-level version):
- Processed value: ~500 ms
- Real-time value: ~100 ms

2.3 UART Communication Parameters

Same as UART Auto Mode.

2.4 Data Frame Format

Identical to UART Automatic Output Mode.

2.5 Output Example

Same numerical example as automatic mode.

3. PWM Automatic Output Mode

3.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	RX	Not used
4	TX	PWM output

3.2 PWM Automatic Behavior

Measurement cycle: 250 ms
Output pulse width represents measured distance.
If no target is detected → output is a fixed pulse width of approximately 45 ms.
Temperature compensation is applied to ensure accuracy in varying environments.

3.3 Distance Calculation

Formula:

S = T × V / 2
Where:

S = distance (cm)
T = PWM high-level pulse width (µs)
V = speed of sound (348 m/s at room temperature)

Simplified formula at room temperature:

S = T / 57.5

Example:
If pulse width T = 10,000 µs →
S = 10000 / 57.5 ≈ 173.9 cm

4. PWM Triggered Output Mode

4.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	RX	Trigger input
4	TX	PWM output

4.2 PWM Triggered Behavior

A falling-edge trigger pulse or UART data initiates a measurement.
TX outputs one PWM high-level pulse representing the measured distance.
Trigger period must be ≥ 70 ms.
If no target is detected → output pulse width ≈ 45 ms.

4.3 Distance Calculation

Same as PWM Automatic Output Mode.

5. Switch Output Mode

5.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input (3.3–5V)
2	GND	Ground
3	RX	Real-time / processed value selection
4	TX	Switch output pin

5.2 Switch Output Behavior

A default threshold distance of 1.5 m is preset at the factory.
SR94 performs a measurement every 100 ms.
If measured distance < threshold → TX outputs high level.
If measured distance ≥ threshold → TX outputs low level.

Response Characteristics:

RX floating or high → processed values, slower but more stable
- Response: ~1.5 s
- Delay: ~2.5 s
RX low → real-time values, faster response
- Response: ~0.3 s
- Delay: ~0.5 s

Important:
The module checks RX level only at power-up. Changing mode requires power cycling.

5.3 Threshold Adjustment via UART Command

Data Format:

Byte	Description
0	Frame Header (0xFB)
1	Command (0x05)
2	Data_H
3	Data_L
4	Checksum

Threshold range: 28–750 cm

6. RS485 Output Mode

6.1 Wiring Definition

Pin	Name	Description
1	VCC	Power input
2	GND	Ground
3	B	RS485 differential negative
4	A	RS485 differential positive

Pin functions are fixed and correspond only to the RS485 output version.

6.2 RS485 Interface Parameters

Electrical level: RS485 differential
Data bits: 8
Stop bit: 1
Parity: None
Default baud rate: 9600 bps

6.3 Modbus-RTU Protocol Parameters

Item	Value
Mode	Modbus-RTU
Error Check	CRC-16/MODBUS
Slave Address	Adjustable, default 0x01
Read Function Code	0x03
Write Function Code	0x06

6.4 Modbus Frame Format

Master → Sensor (Read)

Field	Device Addr	Func Code (0x03)	Register Addr	Register Count	CRC16

Sensor → Master (Read Response)

Field	Device Addr	Func Code	Byte Count	Data	CRC16

Master → Sensor (Write)

Sensor → Master (Write Response)

Same format as master write.

6.5 Modbus Register Table

Measurement & Status Registers

Address	Type	Description	Data Type	Notes
0x0100	Read-only	Processed distance value	Unsigned 16-bit	Output after algorithm processing; unit: mm; response: 500 ms
0x0101	Read-only	Real-time distance value	Unsigned 16-bit	Unit: mm; response ~100 ms
0x0102	Read-only	Temperature	Signed 16-bit	Unit: 0.1°C; resolution 0.5°C

Configuration Registers

Address	Type	Description	Data Type	Notes
0x0200	Read/Write	Slave Address	U16	Range: 0x01–0xFE (0xFF = broadcast)
0x0201	Read/Write	Baud Rate	U16	0x03=9600 (default); other standard rates supported

Registers use high-byte–first order.

6.6 RS485 Communication Examples

Example 1: Read processed distance value

Master:
01 03 01 00 00 01 85 F6
Response:
01 03 02 02 F2 38 A1

Distance: 0x02F2 = 754 mm

Example 2: Read real-time distance

Master:
01 03 01 01 00 01 D4 36
Response:
01 03 02 02 EF F8 A8

Distance: 0x02EF = 751 mm

Example 3: Read temperature

Master:
01 03 01 02 00 01 24 36
Response:
01 03 02 01 2C B8 09

Temperature: 0x012C = 30.0°C

Example 4: Change slave address

Master & Sensor Response:
01 06 02 00 00 05 48 71

Example 5: Change baud rate

Master & Sensor Response:
05 06 02 01 00 01 19 F6
Baud rate set to 2400 bps.

7. Environmental Ratings

7.1 Environmental Limits

Item	Min	Typical	Max	Unit
Storage Temperature	–25	25	80	°C
Storage Humidity	—	65%	90%	RH
Operating Temperature	–15	25	60	°C
Operating Humidity	—	65%	80%	RH

Humidity values specified without condensation.

8. Electrical Ratings

Parameter	Min	Typical	Max	Unit	Notes
Operating Voltage	3.1	5.0	5.25	V	(SR94 RS485: 5–12V)
Peak Current	—	50	75	mA	—
Input Ripple	—	—	50	mV	—
Input Noise	—	—	100	mV	—
ESD Protection	±200 / ±2k	—	—	V	Contact / Air
IEC61000-4-2 ESD	±4k / ±8k	—	—	V	Sensor housing & I/O

9. Beam Pattern Reference

9.1 Without Horn

Wider beam angle
Suitable for shorter-range detection
Measurement data based on PVC cylindrical target (7.5cm diameter, 100cm height)

9.2 With Horn

Narrower beam angle
Suitable for long-range liquid-level measurement
Measurement data validated using cardboard box target (60×50 cm)

(Images omitted but content faithfully preserved.)

10. Model Selection Guide (Mapped to SR94 Variants)

The SR94 series includes multiple versions depending on output mode and acoustic structure.

Application	Features	Output Modes	SR94 Variant
Liquid-Level & Flat-Surface Measurement	Waterproof housing + optional horn; range 28–750 cm; narrow beam	UART Auto / UART Triggered / PWM Auto / PWM Triggered / Switch Output / RS485	SR94-XXXX (customizable)

11. Reliability Test Conditions

Test Item	Conditions	Qty
High Temp & Humidity Operating	65°C, 85% RH, power ON for 72h	3
Low Temp Operating	–20°C, power ON for 72h	3
High Temp & Humidity Storage	80°C, 80% RH, 72h	3
Low Temp Storage	–30°C, 72h	3
Vibration	10–200 Hz, 2.0G, XYZ axes	3
Drop Test	1.2m free fall, 5 times	3

Pass Criteria: Function normal, performance degradation ≤10%.

12. Notes

Mechanical tolerance issues may cause temporary functional abnormalities.
Avoid electromagnetic interference risks; improper system design may affect performance.
For edge-case or extreme condition applications, technical consultation is recommended.
Specifications may change without prior notice.

13. Packaging Specifications

Default packaging is standard industrial packing.
Custom packaging available upon request.
For container shipment, staggered stacking and reinforced corner protection are required.