Lawn sensor: Unterschied zwischen den Versionen
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[[File:capacity.png|caption]] | [[File:capacity.png|caption]] | ||
| − | A lawn sensor should detect if the robot is still on lawn or not. In other words, it should find out if the media directly below the robot is still lawn or something else (air etc.). Therefore, a | + | A lawn sensor should detect if the robot is still on lawn or not. In other words, it should find out if the media directly below the robot is still lawn or something else (air etc.). Therefore, a capacitance sensor can be used as the media below the robot has influence on the capacitance. However, there is no difference in capacitance between lawn and flowers etc. - so you should have a distinct area around your lawn that is different to lawn (e.g. bark mulch). |
| − | == Principle operation == | + | == Principle of operation == |
| − | A lawn sensor could be a copper plate in a closed plastic tube. To find out if the plate has contact with lawn, the | + | A lawn sensor could be a copper plate in a closed plastic tube. To find out if the plate has contact with lawn, the capacitance of this sensor is measured. If the robot is on lawn (lawn is 'dielectric'), the measured capacity increases slightly (by a few pF). |
<gallery> | <gallery> | ||
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| − | Arduino Mega Pin 40 Receive Front -------------| | + | Arduino Mega Pin 40 Receive Front -------------| |
| − | Arduino Mega Pin 41 Send Front --- 2 MOhm --+---| Lawn | + | Arduino Mega Pin 41 Send Front --- 2 MOhm --+---| Lawn |
'''''Back lawn sensor:''''' | '''''Back lawn sensor:''''' | ||
| − | Arduino Mega Pin 42 Receive Back -------------| | + | Arduino Mega Pin 42 Receive Back -------------| |
| − | + | ||
| − | + | ||
| + | Arduino Mega Pin 43 Send Back --- 2 MOhm --+---| Lawn | ||
== Detailed operation == | == Detailed operation == | ||
Initially, the copper plate is discharged by pulling the send pin to low. | Initially, the copper plate is discharged by pulling the send pin to low. | ||
| − | Then send pin is set to 'high' - via a resistor (2 Megaohm) the copper plate is charging slowly. | + | Then the send pin is set to 'high' - via a resistor (2 Megaohm) the copper plate is charging slowly. |
By constantly reading input receiver pin, the Arduino measures the time until it becomes 'high' (capacity measurement). | By constantly reading input receiver pin, the Arduino measures the time until it becomes 'high' (capacity measurement). | ||
Because microcontrollers are fast and precise in time measurement, you can measure very low capacities with this. | Because microcontrollers are fast and precise in time measurement, you can measure very low capacities with this. | ||
Aktuelle Version vom 15. Januar 2015, 15:02 Uhr
Inhaltsverzeichnis
Lawn Sensor
A lawn sensor should detect if the robot is still on lawn or not. In other words, it should find out if the media directly below the robot is still lawn or something else (air etc.). Therefore, a capacitance sensor can be used as the media below the robot has influence on the capacitance. However, there is no difference in capacitance between lawn and flowers etc. - so you should have a distinct area around your lawn that is different to lawn (e.g. bark mulch).
Principle of operation
A lawn sensor could be a copper plate in a closed plastic tube. To find out if the plate has contact with lawn, the capacitance of this sensor is measured. If the robot is on lawn (lawn is 'dielectric'), the measured capacity increases slightly (by a few pF).
Wiring:
Front lawn sensor:
Arduino Mega Pin 40 Receive Front -------------|
Arduino Mega Pin 41 Send Front --- 2 MOhm --+---| Lawn
Back lawn sensor:
Arduino Mega Pin 42 Receive Back -------------|
Arduino Mega Pin 43 Send Back --- 2 MOhm --+---| Lawn
Detailed operation
Initially, the copper plate is discharged by pulling the send pin to low. Then the send pin is set to 'high' - via a resistor (2 Megaohm) the copper plate is charging slowly. By constantly reading input receiver pin, the Arduino measures the time until it becomes 'high' (capacity measurement). Because microcontrollers are fast and precise in time measurement, you can measure very low capacities with this.
