The BST1712 “TPMS” valve is operational outside the tire and transmit every 4 seconds pressure and temperature. Power is supplied by a 3V lithium battery.
The pressure “MEM” sensor is a “Wheastone” bridge with 3kΩ resistance and absorbs , when activated, 1mA.
There is also an operational amplifier while the temperature and battery voltage measurements are done internally to the microcontroller (Texas MSP430F2012 ). A/D conversion process requires about 1.8mA, but these measures are executed in a very short time ( 60µs ).
The “Duty-cycle” is 60µs/6s= 1/100.000 for a total measurement’s mean current of only 18µA.
The valve transmitter has a greater RF power than the SPT17S3 module, sends the data every minute and absorbs 500µA during transmission (two 10ms messages every transmission). The “Duty-cycle” is 20ms/1min = 1/3000 and that leads to a mean consumption of 167µA. These two currents, 18µA and 167µA, must then be summed to the “sleep” microcontroller current and to the components leakage currents (about 300µA).
In the microcontroller it is active just the VLO clock. In every case the average total 24/24 hours current remains typically less than 0.5µA.
Has little influence the fact that sudden changes in the measurements are immediately transmitted.
A sudden drop in tire pressure is fortunately a rare event , as also a parameter change due to maintenance and pressure checks. A CR1225 lithium battery (48mA/h) with a mean 0.5µA discharge current has an expected discharge life between 7 to 10 years, depending on the environmental conditions.
This patent is intended to cover the original concepts and contains a complete explanation on how design a simple RF hardware to generate the RF pulses (the microSP pulses) using standard components normally available on the market.
The basic concept solved by the 3rd patent (not yet published) is the generation, in the temperature range of -40°+125°C (Automotive range) of an RF pulse provided of the necessary stability, with proper raising and falling edges provided of the necessary precision. It also concerns, for industrial reasons, the way of generating these pulses in a repeatable way and using few components, avoiding dedicated ASIC architectures: this concept allows an extended range of industrial application reducing cost of manufacturing.
Simply using two RF Transistors the Micro.sp® hardware can generate particular RF pulses with raising edges measured in less than 100 ns, at the common frequencies used for SRD system (315 - 434 - 868 and 915 MHz).
In the RF power stage time constants are opportunely forged allowing a proper pulse’s shaping and with the necessary raising and falling edges so that the pulse to pulse time is repeatable with the proper precision, to shrug off the “bandwidth” and the “mean current” consumption, still maintaining a “peak power” up to 40 mW ( at 3VDC). The perfection and preciseness of the rising and falling edges is of a primary importance for the “Rx interface” to definitively detect their exact dislocation and timing.
A complete “Telegram” includes a “Preamble”, the ID code; followed by the pressure, temperature and battery tension measures, than followed by some “BIT” of control; this “Telegram” is composed of 34 pulses for a total length of 10ms. While transmitting the 10 ms “Telegram”, in reason of the low pulse “Duty-Cycle”, the mean current absorbed by the battery is lower than 200 µA: it has been possible than to use a small Lithium cell (12.5 mm diameter as the standard CR1225 employed in the PM17), integrating all the architecture, including antenna, inside a standard ISO-TS qualified tyre stem (either “Snap-in” and “Clamp-in”), rather than attaching to the back the standard plastic box, as in the traditional TPMS applications.
This innovative approach to intelligent tire stem permits the use of tire stem qualified and accepted by the car makers, saving huge investments whereas needed in the Tier’s “supply chain” processes.
0 - 12 bar (1200 kPa)
20 bar (1 minute)
-40 +80 °C
-40 +85 °C
Measurement Sampling And TX Period Time
5 seconds (Typ.)
Operating Mode: 3 years
Dimensions (without plastic cap)
40 x 23 x 20,5mm
Direct TPMS systems utilizing traditional standard ASK or FSK modulation have several limitations, the most important being the high energy consumption required by these systems to transmit with acceptable efficiency. In battery-powered devices, this means that either batteries need to be frequently replaced, or energy consumption must be lowered, thus decreasing system performance.
Micro.sp® technology, patented by Ste Industries, is based on short RF pulses transmitted with Pulse Position Modulation (PPM) technique, which guarantees high RF peak power, as required for radio link reliability, but with a very low average power (Power Density) and consequently low current absorption (in the order of 200 µA) during the transmission period. This allows the use of very small primary batteries and also the possibility to employ autonomous energy sources (Energy Scavengers).
Benefits of Micro.sp® technology are: