Overview of the TPMS Tire Pressure Monitoring System:
This system features a low-power solar solution, equipped with an LCD display, solar charging, and automatic wake-up functionality.
The receiver provides configuration options, including settings for temperature units, pressure units, tire matching, temperature ranges, pressure ranges, and factory reset. It can also issue alerts for pressure anomalies, temperature irregularities, and low battery levels. The pressure alarm system includes notifications for both out-of-range conditions and pressure drops. The default pressure range is set between 180-300 kPa. If the pressure exceeds this range, the host will sound an alarm, and the corresponding data will flash. In the case of a pressure drop, the buzzer will emit two beeps, accompanied by the flashing of the relevant data. The temperature alarm includes a high-temperature alert for temperatures exceeding 75°C, which also triggers a buzzer and flashes the associated data. Additionally, a battery level alarm activates if the sensor battery voltage drops below 2.2V, causing the buzzer to sound and the corresponding tire icon to flash.
Utilizing HOPERF’s Wireless Receiver Chip CMT2219B
The CMT2219B is an ultra-low-power, high-performance receiver suitable for a wide range of wireless applications from 127 to 1020 MHz, including OOK and (G)FSK modulation. It is part of the CMOSTEK NextGenRF™ RF product line, which comprises a complete suite of transmitters, receivers, and transceivers. The high integration of the CMT2219B simplifies the peripheral component requirements in system design. Its sensitivity of up to -121 dBm optimizes the link performance of applications. It supports various packet formats and decoding methods, making it adaptable to diverse application requirements. Moreover, the CMT2219B features a 64-byte Rx FIFO, extensive GPIO and interrupt configurations, duty-cycle operation mode, channel listening, high-precision RSSI, low voltage detection, power-on reset, low-frequency clock output, manual fast frequency hopping, and noise output functionalities, enhancing design flexibility and allowing for differentiated product designs. The chip operates within a voltage range of 1.8V to 3.6V. When achieving -121 dBm sensitivity, it consumes only 8.5 mA, and the ultra-low power receive mode can further reduce power consumption. By utilizing the on-chip Low Duty Cycle and SLP (Super Low Power) operational modes, the CMT2219B can achieve microamp-level power consumption for monitoring and wake-up functionalities.
Product Highlights:
· A national brand with independent intellectual property, resilient against any embargo.
· Low power consumption, environmentally friendly and convenient.
· High cost-performance ratio, easy to use and develop.
· Dual service centers in East and South China, providing rapid nationwide technical support.
Hardware Schematic:
Assumed Protocol:
· Modulation: FSK
· Frequency: 433.920 MHz
· Frequency Deviation: 20.0 kHz
· Encoding: Manchester
· Manchester Type: 10=One, 01=Zero
· Transmission Rate: 9.6 kbps
· Load Byte Bit Start: MSB
· Preamble Length: 15 (adjustable based on requirements to reduce power consumption)
· Preamble Data: 0x00
· Synchronization Code Length: 1 byte
· Synchronization Code: 0x01
· Data Length: 8
Product Power Consumption Analysis:
This product is powered by a built-in lithium battery, supplemented by solar charging to extend its operational life. Therefore, power consumption must support battery longevity for several days (generally at least three days) to accommodate overcast weather or situations where the vehicle remains unused (such as in underground garages). The typical receive current for the CMT2219B is 8.5 mA, with a timed sleep current of 0.8 µA; the STM8L052 microcontroller consumes 3 mA in active mode and 0.3 µA in sleep mode. Assuming a lithium battery capacity of 150 mAh, and to achieve a 5-day battery life, considering an 80% battery efficiency, the average power consumption allowed is calculated as follows: 150 × 0.8 / (5 × 24) = 1 mA. Hence, the overall target power consumption for the system is 1 mA. Based on the aforementioned protocol, the duration of the preamble is 15 × 8 / 9.6 = 16.67 ms. Consequently, the listening duration is set to 1.2 ms (approximately covering 20 symbols), with a sleep duration of 10 ms, allowing for two detection cycles during the preamble transmission. Based on this calculation, the average power consumption of the CMT2219B is estimated as 8.5 mA × 1.2 / (1.2 + 10) = 0.91 mA, which is just below the 1 mA target.
Low Power Features of the CMT2219B:
While the CMT2219B's operating current is 8.5 mA, which is not the lowest in the industry, it is quite commendable for a chip in this class. The most significant aspect is the provision of two key features for low-power monitoring:
1. Low Duty Cycle Operating Mode: An embedded state machine operates automatically based on pre-set parameters (mode and duration), allowing the MCU to enter deep sleep mode to save power when no events are triggered.
2. Super Low Power Combined Operating Mode: Depending on pre-set conditions (which are not unique), it offers various combinations to better meet low-power implementation needs. This truly ensures that "there is always a solution that fits your needs."