Summary of TPMS tire pressure gauge scheme:
Low power solar solution, LCD, solar charging, Automatic wake-up
The receiver provides setting functions: including setting temperature unit, pressure unit, tire matching, temperature range, pressure range, and restoring factory settings; The receiver can alarm the abnormal pressure, temperature and battery power; The pressure alarm information includes out of range and pressure drop. The default pressure range is 180-300kpa. If the pressure exceeds this range, the host will sound the buzzer and the corresponding data will flash. When the pressure drops, the buzzer will sound twice and the corresponding data will flash. Temperature alarm information, including high temperature alarm. The high temperature range is 75 ° C. at this time, the buzzer will sound and the corresponding data will flash; Sensor battery alarm: when it is lower than 2.2V, it will alarm, the buzzer will sound, and the corresponding tire icon will flash.
Select Huapu micro wireless receiving chip cmt2219b:
Cmt2219b is an ook, (g) FSK receiver with ultra-low power consumption and high performance, suitable for various 127 to 1020mhz wireless applications. It is part of the CMOS Tek nextgenrf TM RF product line, which includes complete transmitters, receivers and transceivers. The high integration of cmt2219b simplifies the peripheral materials required in the system design. The sensitivity up to - 121dbm optimizes the link performance of the application. It supports a variety of packet formats and decoding methods, so that it can flexibly meet various needs. In addition, cmt2219b also supports 64 byte RX FIFO, rich GPIO and interrupt configuration, duty cycle operation mode, channel listening, high-precision RSSI, low-voltage detection, power on reset, low-frequency clock output, manual fast frequency hopping, quiet output and other functions, which makes application design more flexible and realizes product differentiation design. Cmt2219b operates at 1.8 V to 3.6 v. When the sensitivity reaches - 121dbm, only 8.5ma current is consumed. The ultra-low power receiving mode can further reduce the receiving power consumption of the chip. By using the on-chip lowdutycycle and SLP (supplerlowpower) combined working mode, the monitoring / wake-up function of UA level consumption can be realized.
Product highlights:
National brand, independent intellectual property rights, not afraid of any blockade
Low power consumption, energy saving, environmental protection and convenience
Cost effective, easy to use and easy to develop
East China and South China double service centers, technical support and national rapid response
Hardware schematic diagram:
It is assumed that the agreement is:
Modulation mode: FSK
Frequency: 433.920 MHz
Frequency offset: 20.0 kHz
Code: Manchester
Manchester type: 10 = one, 01 = zero
Transmission rate: 9.6 kbps
Load byte bit start: MSB
Preamble length: 15 (length can be adjusted according to demand to reduce power consumption)
Preamble data: 0x00
Synchronization code length: 1-byte
Synchronization code: 0x01
Data length: 8
Product power consumption planning analysis:
This product is powered by the built-in lithium battery, and solar charging extends the battery life. Therefore, in terms of power consumption, the battery life must be maintained for several days (generally more than 3 days) in order to cope with the actual conditions such as cloudy days or the car owner does not drive for many days (underground garage). Cmt2219b normally receives 8.5ma current and 0.8ua with timed sleep; Stm8l052 master control is 3mA in active mode and 0.3ua in sleep. The capacity of lithium battery is 150mah. Assuming that the battery life of 5 days is met and the battery energy efficiency is 80%, the allowable average power consumption is 150 & times; 0.8 / (5 & times; 24) = 1 mA, so the target power consumption of the whole machine is 1 mA. According to the above protocol analysis, the preamble duration is: 15 & times; 8/9.6 = 16.67ms。 Therefore, the monitoring duration is set to 1.2ms (approximately covering 20 symbols) and the sleep duration is set to 10ms, which can cover two detections within the preamble transmission duration. According to this calculation, the average power consumption of cmt2219b is 8.5ma & times; 1.2 / (1.2 10) = 0.91ma, which is just less than the target planning of 1mA.
Cmt2219b low power setting features:
Although the working current of cmt2219b is 8.5ma, which is not the lowest in the industry, it is very good for this level of chip. The most important is the two weapons that provide low-power monitoring on-chip:
1. Low duty cycle working mode: there is a state machine in the chip, and it operates automatically under the preset working parameters (mode and duration). In case of no event triggering, the MCU can sleep deeply and save power consumption.
2. Supplier low power combination extended working mode: different combinations are made according to preset conditions (not unique) to better meet low power consumption. It can be said that "there is always a suitable demand for you"!
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