Moisture detecting system using semiconductor light sensor with integral charge collection

• US 6,469,291 B2
• Filed: 09/18/2001
• Issued: 10/22/2002
• Est. Priority Date: 01/25/1999
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Bauer, Fred T., Fossum, Eric R., Turnbull, Robert R., Bechtel, Jon H., Nixon, Robert H.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US09/955,445
• Publication Number:
  US 20020020804A1
• Time in Patent Office: 399 Days
• Field of Search: 250/214.R, 250/214.C, 250/214.1, 250/215, 250/573, 250/574, 340/602, 318/483, 327/514
• US Class Current: 250/214.00C
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G01J 1/46 using a capacitor

Abstract

Moisture detection permits moisture removal equipment, such as automotive windshield wipers and defogger systems, to be operated automatically. A system for detecting moisture on a surface includes a light emitter directed at the surface. The presence of moisture is based on the intensity of light from the emitter reflected by the surface and received by a light sensor. The light sensor accumulates charge in response to incident light over a variable integration period.

Claims

1. A system for detecting moisture on a surface comprising:

a light emitter for directing light at the surface;

a light sensor for receiving light that is emitted from the light emitter and strikes the surface, wherein the light sensor accumulates charge in response to incident light over a preselected integration period; and

a control circuit coupled to the light sensor for detecting moisture on the surface based on the intensity of light received by the light sensor.

2. The system of claim 1, wherein the preselected integration period is variable.

3. The system of claim 1, wherein the light sensor comprises:

a light transducer exposed to light operative to accumulate charge in proportion to light incident over the integration period; and

a sensor logic in communication with the exposed light transducer, the sensor logic operative to

(a) determine the light integration period prior to beginning integration,

(b) reset the charge accumulated in the exposed light transducer at the beginning of the determined light integration period,

(c) measure the charge accumulated by the exposed light transducer over the determined light integration period, and

(d) output a pulse having a width based on the measured accumulated exposed light transducer charge.

4. The system of claim 3, wherein the light sensor further comprises a comparator with one input connected to the exposed light transducer and the other input connected to a switched capacitor circuit, the switched capacitor circuit operative to charge a capacitor to a fixed voltage when the switch is closed and to discharge the capacitor at a constant rate when the switch is open, wherein the sensor logic is further operative to close the switch during the determined light integration period and open the switch after the determined light integration period, thereby creating the pulse at the comparator output.

5. The system of claim 4, wherein the light sensor further comprises a second comparator with one input connected to a fixed voltage and the other input connected to the switched capacitor circuit, the second comparator output operative to inhibit output of the determined pulse if the ramp voltage is less than the fixed voltage.

6. The system of claim 3, wherein the light sensor further comprises a light transducer shielded from ambient light, the shielded light transducer having the same construction as the exposed light transducer, the shielded light transducer operative to accumulate charge in proportion to noise over the integration period, wherein the sensor logic is further operative to:

reset the charge accumulated in the shielded light transducer at the beginning of the determined light integration period;

measure the charge accumulated by the shielded light transducer over the determined light integration period; and

output a pulse having a width based on the difference between the measured accumulated exposed light transducer charge and the measured accumulated shielded light transducer charge.

7. The system of claim 6, wherein the light sensor is further operative to:

receive an integration pulse, the width of the integration pulse determining the integration period; and

generate the output pulse after the integration pulse, the difference in time between the end of the integration pulse and the start of the output pulse indicative of the amount of thermal noise in the light sensor.

8. The system of claim 1, wherein the light sensor comprises:

an enclosure having a window for receiving light, the enclosure admitting a power pin, a ground pin, and a signal pin;

an exposed light transducer disposed within the enclosure, the exposed light transducer operative to accumulate charge in proportion to light received through the window incident on the exposed light transducer;

a light-to-pulse circuit disposed within the enclosure and in communication with the exposed light transducer, the power pin, and the ground pin, the light-to-pulse circuit operative to output an output pulse, the output pulse width based on charge accumulated by the exposed light transducer over an integration period; and

a sensor logic disposed within the enclosure, the sensor logic in communication with the light-to-pulse circuit, the power pin, the ground pin, and the signal pin, the sensor logic operative to

(a) receive an integration pulse on the signal pin,

(b) determine the integration period based on the width of the integration pulse, and

(c) output the output pulse on the signal pin.

9. The system of claim 1, wherein the light emitter emits light in the infrared range.

10. A method for detecting moisture on a surface based on the intensity of light received by a light sensor from a light emitter directed at the surface, the method comprising the step of configuring the light sensor to accumulate charge in response to incident light over a preselected integration period.

11. The method of claim 10, wherein the preselected integration period is variable.