In the desire to automate and make my espresso flow more consistent I thought a custom scale would bring some benefits, that is, to stop the shot at a target yield. I’ll get a bit into technical details so feel free to skip forward to pics and video if it gets too much :)
I am using Arduino nano which proved to be quite convenient to program and find documentation.
The weight is measured with a load cell (HX711) which seems to be quite popular and easy to connect and work with from Arduino.
The connection with the espresso machine is done wireless, using 433MHz RF transmitter in the scale and a receiver in the espresso machine that’s connected to the shot switch with a relay. The RF tech is the one used in garage doors and stuff like that :)
The scale is powered by a 18650 cell which is rechargeable via usb.
The case is also custom designed and 3d printed, it has some questionable design choices you may say, but the reason I put the buttons on the side is to have a clean face and to avoid liquid ingress.
In terms of software, nothing ground shaking just few mentions: I am calculating and display the flow (easy thing to add since you can do anything in code), compensate for shot overflow (stop the shot a bit earlier than the target weight), and something I want to later, show a graph with the flow(not sure how it will look on than tiny display).
The espresso machine is Rancilio Silvia Pro.