I need a proximity sensor for a reasonable price that will be read with a PIC Microcontroller. I am sensing feed in a downspout, and want to detect if it is full or empty. One design consideration is that its value should not be extremely altered by remaining residue.
The above link goes to Intersil's article titled Choosing a proximity sensor.
Can you show more information about your design requirments? What you said is not enough at all. First of all, a proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. Like the metal detector at the airport as an example, without any physical contact the device (metal detector) can realize if a piece of metal have passed through the gate or not. Let's get in deep on the operation of the proximity sensor, a proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target.
Examples of Proximity Sensors:
inductive and capacitive proximity sensor
Proximity sensors are not the only solution, you can use to electromechanicl solution to detect water level as an example
I have found out that i need a capacitive type because i am detecting a non-metallic material.
there will be grain based feed going by the sensor, and it should go on when it is in full contact with the feed, not when the feed is flowing past the sensor.
Almost most of the sensors will give you analog output which means by using the analog to digital converter module or by using ADC IC you can read the values of the sensor through a microcontroller chip. What can I understand from your message that you want to detect if the downspout is full or not. I suggest you to check the ultrasonic transducer solution, the ultrasonic transducers can measure the speed of the flow inside pipes so you can get the volume of water inside the downspout, you will be also able to know when the downspout will be full. The ultrasonic solution is efficient, nondestructive and could be cheaper than other solutions.
You can watch this video, it is describing the principle of ultrasonic flow measuring