1. Development Background of Tire Pressure Gauge
Air pressure is the lifeblood of a tire. Too high or too low pressure will shorten its service life. Too low pressure will increase the tire contact area and accelerate the wear of the tire shoulder. Too high pressure will cause excessive stretching and deformation of the tire cord, reduce the elasticity of the tire body, and increase the load on the car during driving. If it encounters an impact, it will cause internal cracks and explosions. At the same time, too high pressure will accelerate the wear of the tire crown and reduce the rolling resistance. An accurate tire pressure gauge can accurately monitor tire pressure at all times to ensure driving safety to the greatest extent . It is best to check it before going on the highway .
2. Technical Parameters
1. Measuring range: ( 1-18) Bar
2. Display mode: 4-digit dynamic display
3. Power supply: 3V ( 2 1.5V AAA batteries )
4. Working environment temperature: ( -20-50) ℃
5. Working environment humidity: < =80%RH
6. Interface : 3 04 stainless steel M14 *1.5 ( external thread ) , special materials and threads can be customized as required
3. LCD display interface
1. Battery status
2. Pressure value
3. Pressure units
4. Hardware Schematic Diagram
The hardware design adopts SDI 5229 as the main control. The reasons for choosing this chip are as follows:
1. The chip provides LDO output, and the sensor is powered by the internal LDO output voltage, thereby reducing power consumption in low power mode. It provides an LCD liquid crystal drive peripheral unit, which can control the LCD display without an external LCD driver chip.
2. When designing the hardware circuit, the tire pressure sensor and the temperature sensor both use 24 - bit high-precision differential ADC. The measurement accuracy is much higher than the single-ended method.
3. When collecting air pressure, RC common mode suppression and differential mode suppression are connected to the sensor to achieve filtering effect, making the ADC reading more stable. In the hardware circuit, a diode is connected to the power supply end of the sensor , and the change of temperature causes the voltage drop of the diode PN junction to be different. A temperature self-compensation effect is achieved.
5. Software Flowchart
6. Features
1. Master control advantage
In the case of a large-scale shortage of imported chips, this solution uses a domestically produced SOC chip , SDI 5229TS, as the main controller MCU . The main control chip integrates a 24 - bit high-precision ADC, which has a high enough advantage in sensor measurement. When entering sleep mode, the MCU main control only consumes 1uA of current. At the same time, the MCU has an internal integrated LCD driver module, and driving the LCD no longer requires an external LCD driver chip.
2. Performance advantages
It is fast enough to measure tire pressure, with a measurement accuracy of 1kPa and a measurement range of 1-700 kPa. It has an NTC to obtain the external ambient temperature in real time and perform temperature compensation on the differential sensor, which greatly reduces the measurement error. After countless tests, the measurement error is far better than the error rate of other manufacturers on the market.
3. Low power consumption
The program will turn off the LED backlight to save energy if there is no tire pressure change within 10 seconds . When the air pressure is lower than 5kpa, it will automatically enter sleep mode after 20 seconds. When entering sleep mode, the current is only 1 to 2 uA, which greatly extends the battery life.
4. LCD display
Real-time display of current air pressure and battery power. There are four units to choose from when displaying air pressure. Select the desired unit mode by pressing the button. After shutting down, it will automatically locate to the last unit mode when it is turned on next time. Compared with traditional mechanical pointer display, it is more accurate and clear.
5. Serial port calibration
The tire pressure is calibrated in a relatively simple and reliable way. During calibration, a verification method is also adopted to verify the reliability of the calibration data and prevent the serial port from sending wrong information. The serial port calibration also supports calibration of four units.
6. Low cost
Since a domestically produced and highly integrated MCU is used, the cost can be reduced to a minimum and no peripheral devices are required. The MCU integrates LCD driver, 24 - bit ADC, 8-bit ADC, low-frequency wake-up and other hardware peripherals. The current tire pressure gauge sample board only has resistors, capacitors, MCU and sensors.
VII. Instructions for use
Power on/off instructions:
The device will automatically turn on after the battery is installed, or you can turn it on by pressing the "ON" button. When the device is turned on, press the "ON button" to turn it off.
Note: Even in the off state, as long as there is air pressure, low-frequency wake-up can be performed to turn on and measure the air pressure. In the on state, even if the "ON" button is not pressed to turn off the machine, as long as the air pressure is less than 5Kpa, the machine can automatically enter the shutdown state after a timing of 20 seconds.
Unit switching instructions:
Press the "UNITS" button to switch the units. There are four units displayed: Kpa, Bar, PSI, and Kgf/ cm2 .
The tire pressure gauge samples are shown in Figures 1 and 2 below.
Figure 1 shows the tire valve connection port. When connected to the tire, the air pressure will enter the tire pressure gauge.
Figure 2 shows the main part of the tire pressure gauge.
Figure 1 Tire connection port
Picture of the second tire pressure gauge sample
8. Conclusion
This tire pressure gauge solution has the characteristics of high measurement accuracy, good reliability, simple operation, large range, low power consumption, low cost, etc. In fact, the principle of the air pump solution is similar, and this tire pressure gauge solution also has great reference value for the air pump solution.
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变色卡
千斤顶
京公网安备 11010802033920号
