Pressure sensor with LED light for beer glass

I am trying to build a light up LED sensor for when a glass is placed on a surface. The idea would be to use like a plexiglass square with a pressure sensor under it, when the sensor gets triggered the light shines up through the glass.

I'd want the light to placed in the center, so what kind of pressure sensor can I use that won't get in the way of the LED?

Thanks

would be to use like a plexiglass square with a pressure sensor under it,

So how is a pressure sensor going to work if it is under the plexiglass? You need to apply the pressure to the sensor. Covering it up is going to get the sensor isolated from the pressure of the glass.

Better use a different type of sensor like a reflective IR sensor, or get fancy cutting out a square of the plexiglass and supporting it from underneath.

Small button load cell (maybe one in each corner? )
HX711 load cell amp

Grumpy_Mike:
So how is a pressure sensor going to work if it is under the plexiglass? You need to apply the pressure to the sensor. Covering it up is going to get the sensor isolated from the pressure of the glass.

Better use a different type of sensor like a reflective IR sensor, or get fancy cutting out a square of the plexiglass and supporting it from underneath.

Well my thought was to of course have the plexiglass and pressure sensor be touching, so if any additional weight was added on top of the plexiglass (a cup), it would turn on an LED. Am I misunderstanding how a pressure sensor works?

But ya, maybe another type of sensor would be better for this application. I'm not well versed on sensors.

Am I misunderstanding how a pressure sensor works?

I would say so, yes.
A pressure sensor like this needs to move a fraction in response to an object being placed on it. If you put it behind a sheet of what ever material then the construction of the box made out of that material will experience the pressure not a sensor on the inside of the box. It is the mechanics of the situation. Either the sensor has to be on the surface or inlayed on the surface so the sensor flexes when pressure is applied.

An array of thermistors under the glass surface could work, to detect where the cold beer is.

Scrap that idea if you're in the UK, where they seem to drink beer at room temp :o
Leo..

Probably your two options are the load cell already mentioned by @evanmars or an FSR (force-sensitive resistor).

If the weight sensor is below or beside the LED, there is no issue of it blocking the LED, so that aspect is really about the mechanical design, not about the sensor choice.

To use a pressure sensor of any sort, FSR or load cell, the sensor has to have pressure applied to it. In this diagram the top situation you will see has no force applied to the sensor, all the force goes through the sides of the enclosure.

In the bottom one you can cut out a gap in the surrounding material and sandwich the sensor between this now floating section of your table and the base of the box. This will work as the pressure is now directly on the sensor. The difficulty is in mechanically making it look neat.

If you make the support a tube and put the sensor between the tube and the base of the box, you can attach your LED to the underside of the floating section of your table.