Dryness detection method for clothes dryer based on pulse width

• US 9,200,842 B2
• Filed: 09/09/2013
• Issued: 12/01/2015
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Hopkins, Thomas L.
• Primary Examiner(s): GRAVINI, STEPHEN MICHAEL
• Application Number:
  US14/022,002
• Publication Number:
  US 20140007453A1
• Time in Patent Office: 813 Days
• Field of Search: 342/82, 343/81, 344/13, 345/27, 345/33, 34/88, 346/01, 68/5.C, 68/5.R, 68/19, 68/20, 813/7, 814/9, 815/9
• US Class Current: 1/1
• CPC Class Codes: D06F 2103/10 expressed as capacitance or resistance
• CPC Class Codes: D06F 2103/44 Current or voltage
• CPC Class Codes: D06F 2105/62 Stopping or disabling machine operation
• CPC Class Codes: D06F 34/18 Condition of the laundry, e.g. nature or weight
• CPC Class Codes: D06F 58/38 of drying, e.g. to achieve the target humidity
• CPC Class Codes: F26B 25/22 Controlling the drying process in dependence on liquid content of solid materials or objects

Abstract

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.

Claims

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.