Bartending by weight

Basically I am a COMPLETE novice when it comes to using items like this, but I want to learn (obviously)

The project I want to build is relatively simple in theory, but I just don't know where to find the knowledge to figure it out:

I want to take an "auto metering" bartender . The thing is I want to add the separate ingredients measured by weight automatically.

So (in theory) you have a mechine set up to make a certain drink. Say we are making Run and Coke: I want a 10% ratio of coke to rum. So 200 grams of coke would need 20 grams of rum, 400 grams would need 40g and so on. Having the weight of the glass pre-programmed in as the tare.

So I fill a glass with 341 grams of coke (random amount) I set the glass on a scale, the 10% (34.1g) is calculated and added to what the total weight should be (375.1g). The system then meters out rum until the proper weight is reached.

The Rum would be gravity fed (no need for pumps or anything just yet.

1)how do I get a digital scale to talk to the Arduino?
2)how do I program the Arduino to control the valve to add the good stuff.
3) is an Arduino the correct platform for this?

I'd rather a "here is the resources to learn how to figure it out" rather than just "here is how to do it." It's the give a man a fish vs teach a man to fish, I want to learn.

I really appreciate any help y'all can give me! If I get this thing working, I'll be making tons of drinks if anyone wants to help me drink them!! Hahha

Thanks again!

This sounds like a really interesting project!

  1. A quick Google seems to suggest that a HX711 board will be one of the more simple ways to interface an Arduino with the load cells found in just about any old set of scales. There are even a few instructables to get you started.

  2. A suitable valve will likely be controllable, via a driver, from one of the digital outputs. It should simply be a case of opening the valve, waiting for the appropriate weight to be measured and then shut it off. You might need to play around with tweaking things to account for the time it takes to actually close the valve once you give it the command but that's a bit of a way down the track.

  3. It most definitely seems like a good project for use with an Arduino.

A couple more tips:

A lot of electronic laboratory scales have RS-232 serial ports built in so would be fairly easy to interface to your Arduino. You might be able to pick up a small second hand one for not very much.

I picked up some small 12v solenoid water valves from a prominent online auction site for a couple of pounds each. I think they were spare parts for office watercoolers so would probably work well with rum etc. (They're "inductive loads" so make sure you learn about them before you wire them up)

A more general tip:

Start practicing now! Get an Arduino and try the Tutorials available on this site. Build up your skills and parts collection in small steps. When you come to make your bartending project it'll be much less confusing!

Good luck!


Using a scale with an RS232 port would make this project nice and easy. The coding/electronics is easy…it is the mechanical/DIY building that would put me off using like the FSR pads.

Step 1: Wait for button press…
Step 2: Take glass weight.
Step 3 : While (weight < (Glass weight + weight of rum)) { keep filling with rum }
Step 4 : Re-weigh contents.
Step 5: While (weight < (glass_weight in step 4 + weight of mixer…)) { keep filling with mixer}
Step 6: Indicate to user job done.

Parts: Solenoid Valve (liquids). ~£5.

Optional extras:

A function that will stop the dispensing of liquids after (x) time to stop any problems causing a bottle of spirit to be emptied on the floor.

Instead of waiting for an initial button push…the arduino just waits for the scale to go from “0” to say over 300g (the weight of a glass) indicating something has been placed there…or use an IR sensor or the like.


Using a scale with an RS232 port would make this project nice and easy. The coding/electronics is easy…it is the mechanical/DIY building that would put me off using like the FSR pads.

Ya’ll are AWESOME!!! Thank you so much!

Johnny010, I am the exact opposite :slight_smile: Mechanical/DIY, fiddling with tangible objects are my thing! Its the coding that I am going to struggle with. My experience with Coding is and HTML class in highschool (I was WAY more interested in my classmates…uh…upper torso region and didn’t pay much attention to the actual lesson) and a bit of python stuff (trying to … borrow…internet at an airport)

You made me think about something as well; Rather than having the weight of the glass already programed into the scale, have a tare button on the system. This would add an extra step, but will allow for any glass to be used.

I thought about using a RS232 capable scale, but I thought about making multiple “Drinxers” (cool name??) for gifts and such. It seems that these scale are quite expensive, when they have the accuracy I want.
I want to use a scale that has the capacity of around 1000 grams and an accuracy of .01 grams. I bought a cheap digital scale with the capacity and accuracy.

Saximus’s suggestion of using an HX711 board sounds like it’s up my alley. Am I correct in thinking that I can simply disassemble the above mentioned scale and wire it to the board?

I am not sure if this is blasphemous on this site ( I apologize if it is looked down on), but would a Raspberry Pi be better for this? In my research, it seems that the Pi might be overkill. Also I think the Arduino would be more stable. Am I thinking correctly.

Thank you again for all of your help!!

The Pi is a power sucker.

Be nice to have this project work off 4AAs.

As far as "tare" the glass...the arduino can do that automatically.

We can assume the first thing on the scale is the glass...and therefore use the arduino can account for the initial weight programatically.

First thing I think of when I see the title is each bar stool has a scale in it and tells you how much you can dispense to that person based on their weight :slight_smile:

When you hit the button to start pouring the coke in, weigh the glass and save the weight. I bet it can weigh the glass before the coke hits it.

Now you have the weight of the glass & coke. Rum is the easy bit.

-jim lee

Thank you for all of your input!! I M extremely appreciative!

One more question:

Which Arduino controller would be best? I’m thinking just a simple Uno or 101? Is that going to be enough functionality?


This could be done on an Attiny85…

But for simplicity and if you are very new to this, stick with an UNO for the prototype and then if you feel confident later, try “Arduino on a breadboard” for extra power saving ;).