Sensors for tip box. Which ones?

I'm planning on making a tip box like this: http://i.imgur.com/DgCPV07.gif

Now instead of the button on which the coin lays, I want to put a sensor that can detect coins. I'm thinking of an inductive proximity sensor. Is this a good choice or are there other/better options?

Also when the coin gets dragged in, the box needs to know what kind of coin is dragged inside. I'm thinking of a little container inside the box where all the coins end up with a scale underneath. Using the weight of the coins I can detect which coin it is. For example: begin_weight = 0 grams, the little paw drags in a coin worth of 2 euros which is 8,50 grams = weight_measured. Then weight_measured - begin_weight = weight_of_coin. Depending on that weight, a different little soundtrack will play. Which kind of sensors do I use for this? A load cell or some other/better options? Or is there a better way to detect which coin has been dragged inside?

Thanks in advance. Sorry for my bad English, it's not my native language.

That is the funniest useless machine I have seen :smiley:
This one looks a lot like it : - YouTube

Yes, inductive sensor will work. You could make your own circuit with a detection coil, like a metal detector.

To measuring the weight, only a load cell will be accurate.
Measuring the size of the coin will be very hard in such a small box, and measure the kind of metal mix is also very hard. I think that just measuring the weight will be okay for this project. But people might use all kind of metal pieces.

Yes, it's a pretty funny machine xD

And thanks for the info. Now I can change it. :grin:

The HX711 is often used with a load cell. That is a lot more accurate than an OpAmp and the Arduino analog input. They are very cheap on Ebay.
With the HX711 you don't have worry about the weight of the box where the coins drop in. It is accurate enough to measure the coin even with a "heavy" box.

I can't find someone who made a review of the inside. I guess it is a single servo motor.
It can be bought at amazon, and for example here : Itazura Bank Pet Coin Box | Japan Trend Shop

The hx711 + a load cell can weigh the difference between eurocents?

Perhaps not with a load cell for 100kg, but for a smaller load cell, yes.
On Ebay are very cheap weighting scales. Search on Ebay for : pocket scale
I have one of those, and there is a little load cell inside.
They are 0.1 gram or 0.01 gram accurate.

This one:
http://www.aliexpress.com/item/Electronic-Balance-Four-Wire-Weighing-Load-Cell-Sensor-100g/32218768036.html

  • the hx711 should work?

Yes, I think so. It is a nice small load cell with 4 wires.