I am looking to start a new project for a smart fridge that can identify what specific items have been removed form it.
After doing some research there are two start-up with two different technologies from where im gathering some inspiration.
Solution #1(shelfx): They use digital scale to measure the weight of the items inside the fridge and then are able to recognize what you have taken by using a combination of (what scale you use + total weight taken). For this method i believe they actually use some sort of Force Sensitive Resistor.
Solution #2(Leanbox): They rigged their fridges with an rfid reader and packed everything inside with a tag.
Now, I personally like the second solution that uses RFID, because you can identify every single product (not just a product class) and because it seems simpler. However i am not sure of what type of sensor do they use?
As i plan how to create the system, i am thinking that i will need to use passive RFID tags and that there are two places where you could put the antena. Either have a very powerful antena ( i don’t have the slightest idea of which one) on the door and detect as things leave the fridge. Or put many small antenas at the bottom of the fridge shelves/racks, and have them always on a always on mode where they can identify the products that have been taken because you no longer can read them.
Anyways i am still a bit early as you can probably tell, but im looking for some guidance from people with experience on how better do this project.
Near Field Communications (NFC) RFID (reader built into most all new smart phones).
Tags are expensive: like $0.80 each, so they need to go on a container as they’re too costly to be disposable.
Zillions of these in use. NFC reader kit available maybe here, Adafruit, etc.
I use the reader built into my HTC One phone, linked to the LAN/WAN. That phone + freeware will also read, optically, bar code labels and the 2D labels using the camera. Rather cumbersome though.
Passive RFID tags have a few mm (not cm) range; awkward.
Smart Frig. Inventory - OK demo, not practical for daily use.
The idea for the RFID reader would be to place them bellow each fridge rack to that they can detect products within that area. Ideally i would only use one or two per rack (if a fridge rack is 3ft x4ft).
From the research i have done there are 3 different frequencies for the RFID tags and some can be used as far as a couple of meters away.
There are several different kinds of Passive RFID tags.
NFC (Near Field Tags) operate at 13MHz and have very short range. The advantage is (as mentioned) Android based cell phones can read NFC tags.
UHF tags operate in the US in the 902-928 MHz ISM band and have a range of about 11 feet - sufficient for the refridgerator project. The readers tend to be more expensive.
Passive UHF tag prices depend on style and quantity - but you have probably seen them embedded in your product labels in stores such as American Apparel and JC Penny. In the quantities they use - tags are around $0.06 each (6 cents) - you can buy tags from many sources.
Passive UHF tags use “EPC Gen2” protocols (Electronic Product Code - Generation 2). Tutorials are available on-line; a good source is Impinj.com.
