SonarExtenderI2C
Connect up to four Ultrasonic sensor HC-SR04 via I2C to an Arduino or Raspberry Pi
Connection
Ultrasonic sensor connection (CN3-CN6)
| Pin | Function |
|---|---|
| 1 | 5V |
| 2 | Trigger |
| 3 | Echo |
| 4 | GND |
Mikrocontroller connection (P1)
| Pin | Function |
|---|---|
| 1 | GND |
| 2 | SCL |
| 3 | SDA |
| 4 | Logic voltage (3V3/ 5V) |
| 5 | Interrupt pin |
| 6 | Ultrasonic sensor voltage (5V) |
How to use
The sensorboard is based on the 16-bit I2C Expander TCA9535 with the slave address 0x20. There are two operating modes for the device. In the manual mode You can evaluate every sensor on Your own, in the automatic mode, all four sensors are evaluated sequentially and an interrupt is rising when all four sensors are triggered once.
TCA9535 pinout
| Pin | Function |
|---|---|
| P0 | DECODE0 |
| P1 | DECODE1 |
| P2 | DECODE2 |
| P3 | STATUS ECHO |
| P4 | TRIGGER0 |
| P5 | TRIGGER1 |
| P6 | TRIGGER2 |
| P7 | TRIGGER3 |
| P10 | D0 |
| P11 | D1 |
| P12 | D2 |
| P13 | D3 |
| P14 | D4 |
| P15 | D5 |
| P16 | D6 |
| P17 | D7 |
Manual mode
1. Initiate trigger signal
Before every manual measurement make sure, that TRIGGER0-TRIGGER3 are low and DECODE0-DECODE2 are smaller than 4 in binary. In manual mode You can trigger a sensor by setting TRIGGER0-TRIGGER3 high according to which sensors You want to use:
| TRIGGER0 | TRIGGER1 | TRIGGER2 | TRIGGER3 | |
|---|---|---|---|---|
| Sensor 0 | H | L | L | L |
| Sensor 1 | L | H | L | L |
| Sensor 2 | L | L | H | L |
| Sensor 3 | L | L | L | H |
2. Wait for measurements to finish
If all measurements are finished STATUS ECHO will go high. Here it is important to wait a minimum of 100ms after triggering the sensor.
3. Evaluate the measurement result
The sensorboard has a 8-bit counter for every sensor, that is started and stopped automatically according to the measurement cycles. You can read the data on D0-D7 by setting DECODE0-DECODE2 to the right counter:
| DECODE0 | DECODE1 | DECODE2 | |
|---|---|---|---|
| Sensor 0 | L | L | L |
| Sensor 1 | H | L | L |
| Sensor 2 | L | H | L |
| Sensor 3 | H | H | L |
As the counters are running at a 10kHz frequency and the ultrasonic signal needs 29.4us to travel one centimeter, You can calculate the distance to an object in cm by the following formular: distance = 100*countervalue/2/29.4. The maximum distance is 425cm with an accuracy of 4.25cm.
Automatic mode
Starting and stopping the automatic mode
To start the automatic mode, the DECODE Pins need to be set to binary 4, in any other configuration it will not run. Then all sensors will be triggered one after another.
Evaluating the automatic mode results
If all sensors are triggered, the interrupt pin wil rise and You can evaluate the results like in section 2.) of the manual mode.
Pausing the automatic mode
To pause the automatic mode, simply set the DECODE Pins to binary 5. In opposite to binary 4, it won't reset and continue with the next sensor.
Arduino lib
https://github.com/wuehr1999/SonarExtenderI2C-Library