Imagine: At a construction site, each time the trigger is pressed, or the drill/screwdriver is rotated at full speed, the user does not respond even if the user hardly touches the trigger.
No one wants to experience these situations, but these things happen when the trigger of the tool wears out. This is especially true for conventional resistance potentiometers, which wear out over time and in harsh environments (humidity, extreme temperatures, excessive dust, etc.).
One solution is to replace the resistance potentiometer with a capacitive sensing based potentiometer that increases the life of the power tool without the need to perform costly repairs and replacement of the trigger switch.
TI Designs' <65μA reference design (TIDA-00475) non-contact position sensor for variable speed trigger switches demonstrates a solution to replace resistance potentiometers with more reliable trigger switch applications. Figure 1 shows the block diagram of TIDA-00475.
Figure 1: Block diagram of TIDA-00475
The reference design includes the MSP430G2553 microcontroller (MCU) with pin oscillator technology that measures the capacitance of the electrodes and the TPS7A16 low-dropout regulator, which enables the design of a battery pack powered by up to 10 cells in series. At the same time, only 65μA of electrical energy is consumed during operation; less than 1.2μA of electrical energy is consumed during shutdown.
Once the PCB tongue containing the electrode is pressed down, the capacitance change can be accurately measured, as shown in Figure 2.
Figure 2: Capacitance generated between the electrode and the ground shield
Even when the motherboard is attached to a hammer drill powered directly by the battery pack, the reference design guide contains a complete test demonstrating its good performance, just as it is presented in the final operation.
Figure 3: Accuracy to the impact drill
Another option for replacing the resistor potentiometer is to use the new MSP430TM MCU FRAM CapTIvate TM touch technology, which is in the most noise-resistant capacitive touch microcontroller and configures capacitive buttons and slides with very low power consumption. Block, wheel and proximity sensor combination.
In addition to a precise potentiometer, CapTIvate-based solutions offer the possibility to add additional features, including:
Button/slider for speed control.
Clamp detection to wake up the power tool and save battery power.
If the user touches the dangerous parts of the power tool, it can be safely closed.
Button/slider/wheel for additional control of the tool.
Improve the reliability of today's trigger switches with TI's capacitive solutions.
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