SparkFun Electronics Forum

So I bought a proximity sensor and it creates the signal when there is nothing in front of it. I need the opposite I need the signal to come when something comes in front of it. What do I need to buy? This is what I bought https://www.amazon.com/gp/aw/d/B019DT0U ... 300U&psc=1

Please post a wiring diagram and explain what you mean by "creates a signal".

How do you want to use this sensor?

So I am trying to create a system that when something comes within one inch of the sensor that it sets off a buzzer. Right now, with the sensor that I have, if something is not within one in of the sensor the buzzer goes off.

The question we need answered is "what is that signal?". In terms of voltage and current changes. You were not asked how you want other devices to (re)act on that.

Often the manufacturer has datasheets for the product. That amazon link is a bit of help (thanks to some reviewers), but maybe the label on the device explains more who made it and where/which site to look for more information.

From the Amazon link it looks like you bought an LJC30A3-H-Z/AY which, using Google, I found what looks to be a manufacturer catalog page from http://www.chinahwe.net. From that page it looks like it is a normally closed PNP type. I'm guessing that means the three wires behave like the base, collector, and emitter terminals of a PNP transistor. I further guess that since it's normally closed, the transistor conducts when nothing is near the sensor and stops conducting when an object approaches the sensor. Given this, I think you should be able to feed the signal into an inverter circuit (NPN transistor, IC, etc.) and get what you want. Or, based on the page I found from Google, you could just get an LJC30A3-H-Z/BY which is the normally open version of the sensor.

Keep in mind though that I have no experience using this sensor and the information given above came from a 5 minute Google search, i.e. this has been a giant SWAG. As others have commented, more info would be helpful!

EDIT: Here's a better link - http://www.chinahwe.net/products/ljc30-ID221.html

Whenever you bought any kind of sensor make sure that it is properly calibrated and configured because in my point of view lot of sensors lack proper calibration that's why they produce operational errors.