So I want to automate a part of a buffet, with about 60 trays of food. The job is to check if one of the trays is empty, and send the data to an arduino at the counter which will send serial input to an arduino at a TV in the kitchen which will display the item that needs to be replenished. How can this be done? I got everything down except how to check if the trays of food are full or not.
darkfighter:
So I want to automate a part of a buffet, with about 60 trays of food. The job is to check if one of the trays is empty, and send the data to an arduino at the counter which will send serial input to an arduino at a TV in the kitchen which will display the item that needs to be replenished. How can this be done? I got everything down except how to check if the trays of food are full or not.
A weight sensor?
If the tray is heavy, it is full
If it is not, it is empty
Weight sensor would be a good choice. You not only sense it is empty (or near empty), you can also plot out its consumption rate etc as a function of time. I would try 4 force gauges with one at each corner. On the other hand, 60 trays means up to 240 force gauges, i.e. a lot of money to build. It's probably ok to just hire someone to monitor the trays.
Some cheap ultrasonic distance sensors maybe? Calibrated to 'empty' distance from where it's mounted to roughly the surface of an empty tray. When food gets low, distance increases, with fine tuning of the numbers it could work.
Keep it simple? Just provide a box with a button next to each tray with the words "more please!" written on it. Use wipe-clean buttons.
Hi,
Have the trays sit on a simple micro switch, spring load the base that the tray sits on, loaded base sits down on micro switch, empty tray the base springs up and switch opens.
You don't need to know the mass of the food, just how much an empty tray is.
You then have a plate empty/ plate loaded output.
You can then either resistor/analog sense the switches or multiplex them, the scan time can be as slow as a minute.
Tom... 
TomGeorge:
Hi,
Have the trays sit on a simple micro switch, spring load the base that the tray sits on, loaded base sits down on micro switch, empty tray the base springs up and switch opens.
You don't need to know the mass of the food, just how much an empty tray is.You then have a plate empty/ plate loaded output.
You can then either resistor/analog sense the switches or multiplex them, the scan time can be as slow as a minute.
Tom...
Would hardly be a microswitch if it has to lift a big heavy tray. You'd have to spring the tray juuust right with other springs so the empty and not-empty are within the tiny tiny weight diff of the microswitch.
Then you'd get screwed over if customers leave tongs/serving spoons in the tray :o
And for wet food items, the trays are never really empty. No one will scrape up the last bits of marinara, they'd just wait for a new tray. Empty tray weight will vary widely. Weight-based sensors will be very inflexible to changing the food items.
Couple good answers here.
spring with microswitch would work great and much less complicated than a load cell.
the problem starts with the tare weight. when you fill your buffet tray with water and add heat, you have created a variable weight container that will continue to loose weight as the steam evaporates.
as for the food, a half full pan of Chicken Tikka weights much less than a half full tray of Saag Paneer.
If you could keep all the chaffing dishes filled to the same level with water at all times, you would only need to weigh your food.
With a spring and microswitch, you could have multiple settings. wet dishes like Lamb Kourma would weigh about the same as all other wet dishes, Tandori Chicken or Vegetable Samos's would weigh much less as there was no wet sauce.
salads and such would weight even less.
with such a variety, one might assume you have a large table with a single heated water bath and could control water height very accurately. in that case, you could make hockey puck type devices, that are adjustable for weight and place them under each chef pan. put them in the water.
but, in the end, a simple web cam over the dishes would prove to be much easier.
For detecting food I suggest a rat.
regards
Allan
allanhurst:
For detecting food I suggest a rat.regards
Allan
I assume that one reason they never put Ratatouille on the buffet is because if someone in the kitchen yelled out WE'RE ALMOST OUT OF RAT ..... it would not be such a good result.
In reality, though, the food still needs to be brought out. The person who refills the food just needs to take note of what items are low and talk to the kitchen.
Auto detecting when an item is low only makes sense when you're also automating food refilling like with a dump chute, which would probably be neat but offputting.
Unless you specifically hire severely mentally incapacitated workers who have a hard limit of only being able to replace trays but are unable to also notice food levels, this project serves benefit.
Hmm, Dave really has a point with the use of micro switches. Btw, he got the items in the buffet spot on. It looks like he had went there by chance, since it looks like he is in NJ too. But the primary purpose of this is to automate the lazy indian chefs that we have to keep up with the asian chefs in our fusion buffet. The primary problem is that after you tell them what has run out, they dont seem to remember at all. The display I guess has a good use for it then.