Input Circuit Rejecting Water Contamination in Tractor Switches
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Solution Overview
Problem
Existing safety circuits in tractors, grass mowing machines, and utility vehicles face issues with water contamination in switches, leading to false indications and excessive heat dissipation, particularly with the use of microcontrollers, which can result in unsafe vehicle operation and reduced component lifespan.
Innovation Solution
A low-cost circuit design that includes power transistors connected through diodes and resistors to input switches, allowing for short intervals of higher current draw to differentiate between water contamination and valid switch closures, while minimizing power dissipation and using a microcontroller to manage switch states and vehicle functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If microcontrollers with high impedance inputs are used, then device complexity is reduced, but water in the switch appears as a valid closure causing false indications
Solution Approach 1:
The circuit applies periodic pulsed current through the switch rather than continuous current. A transistor periodically pulses current through the switch at specific intervals, allowing the microcontroller to sample the switch state during these pulses. This periodic action enables the high-impedance microcontroller input to temporarily overcome water resistance during sampling moments without continuous power dissipation.
Solution Approach 2:
The circuit pre-charges capacitors connected in parallel with the switches before sampling occurs. These capacitors are charged during a pre-charge phase and then discharge through the switch during the sampling phase, providing an initial current surge that helps overcome water resistance temporarily. This preliminary charging action prepares the circuit for accurate switch state detection.
2Measurement precision
If continuous current is drawn through the switch, then switch state detection is improved, but excessive heat is dissipated reducing component lifespan
Solution Approach 1:
The circuit uses periodic pulsed current instead of continuous current to detect switch state. The transistor switches on briefly at predetermined intervals to pulse current through the switch and associated capacitors, then switches off. This periodic action provides sufficient current for accurate detection during pulse moments while minimizing average power dissipation and heat generation, thereby extending component lifespan.
Solution Approach 2:
The circuit applies excessive current temporarily during pulsed moments to ensure reliable switch state detection, then reduces to minimal or zero current between pulses. The capacitor charging during pulses creates temporary high current conditions sufficient to overcome water resistance, but the duty cycle is kept low enough that average power dissipation remains minimal, preventing excessive heat buildup.
3Productivity
If voltage threshold is lowered to accommodate low battery voltage, then productivity is improved, but sensitivity to water in switch increases causing false indications
Solution Approach 1:
The circuit uses periodic sampling with pulsed current to detect switch state independently of the microcontroller's continuous voltage threshold. During each pulse, current is forced through the switch to charge capacitors, and the resulting voltage change is detected during this specific time window. This periodic detection method works reliably even when battery voltage is low, without requiring the microcontroller to lower its voltage threshold and become sensitive to water resistance.
Solution Approach 2:
The circuit introduces capacitors as intermediary elements between the switch and the microcontroller input. These capacitors are charged through the switch during pulsed moments and then their voltage state is sampled by the microcontroller. This intermediary mechanism translates the switch's low-resistance closure state into a detectable voltage change that works reliably across a wide range of battery voltages, eliminating the need to lower the voltage threshold.
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 circuit effectively rejects water as an open input switch, ensuring safe vehicle operation with reduced heat generation and cost, improving the reliability of safety circuits by accurately sensing switch states and reducing false indications.
Implementation Method 1
A first capacitor may be connected in parallel with the switch. A second capacitor may be connected between the base of the power transistor and ground. The power transistor may be pulsed to a on condition to charge the capacitors
Implementation Method 2
A diode may be connected through a resistor to the switch or switches
Data Source
AI summary
An input circuit for a tractor includes one or more switches having open and closed positions, based on operating characteristics of the tractor, and a power transistor drawing a threshold current through the switches during short intervals during which the switch states are sensed by a microcontroller.