Dryness detection method for clothes dryer based on pulse width
View Patent ↗A device and method are provided for detecting a root moisture content of clothing in a clothes dryer. The dryer has two conducting bars situated in the dryer bin. A pulse generator circuit is coupled to the conducting bars. A microcontroller is coupled to an output of the pulse generator circuit. The pulse generator circuit generates a pulse when wet clothing contacts the conducting bars in the dryer bin. The microcontroller receives the pulses and counts the pulses that are longer than a threshold length. The microcontroller issues a termination signal based on the number of counted pulses.
1. A method, comprising:
sensing a resistance between two conductors in a dryer bin of a clothes dryer;
generating a pulse when the resistance is lower than a threshold resistance, a length of the pulse corresponding to a length of time that the resistance is lower than the threshold resistance;
comparing the length of the pulse to a threshold time; and
outputting a termination signal based on a rate of pulses that are longer than the threshold time.
2. The method of claim 1 , comprising:
counting the number of pulses that are longer than the threshold time during a plurality of counting periods; and
outputting the termination signal if a number of pulses longer than the threshold time exceeds a threshold number during at least one of the counting periods.
3. The method of claim 1 wherein the termination signal ends the drying cycle.
4. The method of claim 1 wherein comparing comprises:
triggering an interrupt to a microcontroller on a leading edge of the pulse; and
counting the pulse if the pulse is longer than the interrupt to the microcontroller.
5. The method of claim 1 wherein comparing comprises:
starting a timer on a leading edge of the pulse; and
comparing the length of the pulse to the threshold time as counted by the timer.
6. The method of claim 1 wherein generating the pulse comprises:
charging a capacitor when the resistance between the two conductors is less than the threshold resistance, the capacitor being coupled to the two conductors; and
activating a switch when a voltage on the capacitor reaches a threshold voltage, the switch being coupled to the capacitor.
7. A method, comprising:
drying clothes in a dryer bin of a clothes dryer;
generating a pulse if the resistance of the clothes is less than a threshold resistance;
comparing a length of the pulse to a threshold time;
counting pulses which are longer than the threshold time; and
terminating a drying cycle if a rate of occurrence of counted pulses is less than a threshold rate.
8. The method of claim 7 wherein generating the pulse comprises:
charging a capacitor to a voltage dependent upon the resistance of the clothes;
turning on a transistor coupled to the capacitor when the voltage reaches a threshold voltage; and
outputting the pulse to a microcontroller when the transistor turns on.
9. A device, comprising:
a pulse generator circuit configured to generate a pulse when a resistance of an item is detected to be less than a threshold resistance;
a microcontroller configured to receive the pulse and to compare a length of the pulse to a threshold time; and
a counter coupled to the processor, the microcontroller being configured to increment the counter if the pulse is longer than the threshold time.
10. The device of claim 9 wherein the detection circuit is coupled to a first and a second conductor each positioned in a dryer bin of a clothes dryer.
11. The device of claim 9 wherein the item is clothes.
12. The device of claim 11 wherein a moisture content of the item is detected by sensing a resistance between the first and the second conductor when the first and the second conductor are in contact with the item.