Light sensor

Thread Starter

curiousity

Joined Aug 22, 2019
11
Can ambient light sensor detect contact between two surface?
And how sensitive it is?

Or anyone can advice
1. What is the technology which can detect very minimal presence of light?
2.What is technology can detect contact between two different things and can tell user it is not in contact anymore,
 

peterdeco

Joined Oct 8, 2019
114
A solar cell can detect light. A Light Dependent Resistor will change resistance with light. A proximity detector can detect contact between 2 objects.
 

peterdeco

Joined Oct 8, 2019
114
We use an infrared transmitter/detector at work to detect an objects distance to the sensor. However the detection range is about 1 inch on a reflective surface.
 

Thread Starter

curiousity

Joined Aug 22, 2019
11
Is there any technology which is very sensitive. Maybe can detect to micro measurement where able to detect the object no longer contact?
 

peterdeco

Joined Oct 8, 2019
114
The infrared sensor I mentioned can be adjusted with a circuit to detect proximity of an object a millimeter away. When I get to work today I will look up the part number and post the spec's.
 

jpanhalt

Joined Jan 18, 2008
9,079
Is there any technology which is very sensitive. Maybe can detect to micro measurement where able to detect the object no longer contact?
Yes. You can detect touch of two metallic objects by conductivity. Also, you can detect mating (assuming the surfaces mate) by light, as sensitivity for light in what is otherwise darkness is extremely high.
 

Thread Starter

curiousity

Joined Aug 22, 2019
11
Thank you.
Actually Im thinking for my final year project to develop sensor for detect contact between dressing(like tegaderm)to patient skin.So the sensor able to tell healthcare profesional when it getting loose.

Which is the nearest technology possible for this application?

Thank you
 

peterdeco

Joined Oct 8, 2019
114
This is also something we use at work. It is called a Force Sensing Resistor or FSR. It's resistance decreases with the amount of pressure on it. We use it with an adjustable circuit to detect a preset amount of pressure on it. It could detect something that is worn gets loose.
 

jpanhalt

Joined Jan 18, 2008
9,079
Tegaderm does not apply much pressure per se, unless it is wrapped.

Here are 5 "off the cuff" ideas:
1) Electrical capacitance (like a touch switch): Would require 2 electrodes -- one on the patient and one one the pad. EKG electrodes probably OK and hospitalized patient probably already has at least one such electrode attached.

2) Air pressure under the pad: The pad is intentionally breathable, but is not open when applied to the skin. A continuous very low flow of filtered air could detect when the dressing comes loose by a loss in pressure.

3) Ultrasound: A TX/RX combo on the dressing could detect whether it comes loose, but expensive and a bit inconvenient to wear.

4) Noise (crepitus): A loose dressing will move more relative to the patient's skin than one that adheres properly and produce more noise with regular movements. It would also affect capacitance and resistance (see #1).

5) Temperature: A dressing that is properly attached will be warmed more by the patient's skin than a loose one is. One could attach a TC or other temperature detector and detect changes.

As for my preference, #5 is probably the easiest to implement in a hospital setting. Of course, if the patient is ambulatory, there would be lots of problems with any of those ideas. Why would you need to monitor a conscious and ambulatory patient?
 
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