Capacitive Proximity Switch Circuit With Impedance Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing capacitive proximity switches have a low output signal distance, necessitating the use of expensive analog-digital-converters for readout, which increases costs in household appliances.
Innovation Solution
A circuit for a capacitive proximity switch utilizing a bipolar pnp-transistor as an impedance converter, along with specific resistor configurations and a measuring capacitor that varies capacitance with object proximity, enhancing signal distance and allowing for digital output without the need for an ADC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive proximity switch circuits are used, then the circuit structure is simple, but the output signal distance is low (20%) requiring expensive ADCs
Solution Approach 1:
The patent introduces an impedance converter as an intermediary component between the measuring capacitor and output capacitor. This impedance converter transforms the impedance characteristics to achieve significantly improved output signal distance (80-90%) without requiring complex ADC circuits, thus resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent changes key circuit parameters including using a bipolar pnp-transistor for impedance conversion, selecting specific resistor values (R1: 0.3-2.5 MOhm, R2: 2.5-6.9 MOhm), and configuring capacitor values (C1: 10-100 pF, C2: 10-100 nF) to optimize the output signal distance while maintaining circuit simplicity
2Measurement precision
If ADCs are used to read out the proximity switch, then measurement precision is improved, but costs increase
Solution Approach 1:
The patent replaces expensive ADC components with a simpler circuit implementation using standard electronic components (transistor, resistors, capacitors) that are cheaper and easier to manufacture, while achieving the same measurement precision through optimized circuit design
Solution Approach 2:
By optimizing circuit parameters (impedance values, resistance, capacitance) the patent achieves high measurement precision without requiring expensive ADC conversion circuits, thereby reducing manufacturing costs
3Difficulty of detecting and measuring
If the measuring capacitor varies capacitance with proximity, then detection capability is improved, but susceptibility to electromagnetic disturbances increases
Solution Approach 1:
The impedance converter acts as an intermediary that isolates the measuring capacitor from electromagnetic disturbances while preserving the detection capability. The bipolar pnp-transistor configuration provides impedance transformation that enhances signal detection without increasing susceptibility to electromagnetic interference
Solution Approach 2:
The patent uses simple, robust passive components (resistors, capacitors, transistor) that are inherently more resistant to electromagnetic disturbances compared to complex integrated ADC circuits, while maintaining detection capability through optimized component selection and circuit configuration
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly increases output signal distance, enabling cost savings by eliminating the need for ADCs and providing robustness against electromagnetic and high-frequency disturbances, with a signal distance of 80-90% compared to 20% in prior art.
Implementation Method 1
The measuring capacitor is configured to vary its capacity depending on a distance or proximity of a nearby object, in particular a finger of a user
Implementation Method 2
The impedance converter is a pnp-transistor, in particular a bipolar pnp-transistor, an emitter of the pnp-Transistor forming the first pole of the impedance converter. A collector of the pnp-Transistor forms the second pole of the impedance converter
Implementation Method 3
The circuit further comprises a first diode having an anode and a cathode. The anode of the first diode is connected to the second pole of the voltage source... The circuit comprises a second diode having an anode and a cathode. The anode of the second diode is connected to the second pole of the impedance converter
Implementation Method 4
The circuit also comprises a voltage source configured to deliver an alternating signal. The voltage source has a first pole and a second pole
Data Source
Figure 1
AI summary
The invention relates to a circuit for a capacitive proximity switch comprising an impedance converter, the circuit delivering a high output signal distance. The invention relates further to a proximity switch comprising such a circuit and to a household appliance comprising such a proximity switch.