Yet another smart(sort of) espresso coffee scale, modded dirty but cheap.

Acaia produces excellent coffee scales, especially their espresso scale, aka. Acaia Lunar. It features some very useful functions, such as:

• Negative weight auto tare
• Positive weight auto tare and auto start timer
• Auto stop timer after last drip
• ...

As a heavy espresso drinker, and a new-bie arduino user, I want to use some cheap scales, and find a way to mod them into an Acaia-like espreeso scale.

I bought nearly every coffee scale under 200 RMB(￥) or about 30 USD($). I took them apart, did some research, and found the following information:

• All scales share one same component called Loadcell. Loadcell usually has 4 wires, which should be in red, black, green and white.
• The Loadcell does nothing with reading speed.
• The Loadcell dees little with reading accuricy. (in coffee making)
• Some large scales don't have much space inside, and supprisingly, some quite compact scales do.(good for mod)

• MCU: Arduino Nano (￥21.6 $3.34)
• Loadcell: Comes with the scale (￥15.3 $2.36)
• ADC:HX711 @10Hz (￥2.45 $0.38)
• Display: 1.3 inch SSD1306 OLED IIC (￥22.5 $3.48)
• Battery: A lithium battery which fits inside 200mAh(type 402030) (￥10.8 $1.67)
• 3.7v to 5V converter(for lithium battery, with charge function) (￥3.3 $0.51)
• Battery(if you want to use the original battery bay): Any stock AA/AAA battery comes with the scale
• 1.53with 3v to 5v converter. (￥2.1 $0.32)
• Total cost（~￥75.95 ~$11.73）which is significantly less than an Acaia.

• HX711_ADC https://github.com/olkal/HX711_ADC
• Adafruit_SSD1306 https://github.com/adafruit/Adafruit_SSD1306
• Stopwatch_RT https://github.com/RobTillaart/Stopwatch_RT

• Negative weight auto tare
• Positive weight auto tare and auto start timer
• Auto stop timer after last drip
• Brew ratio(now only fixed as 20g coffee, which I usually use)

• Button support
• Low power mode(however, I want to use an On/Off switch to save the fuzz)
• Coffee bean/ground holder cup memorize(by weight/by nfc), to only weigh the coffee and not start timer.
• Espresso machine wireless control(phycicle push button/use relay)

• Bluetooth support for smartphone
  which I still don't get the point to use phone during coffee making, I used the Acaia Pearl S and Acaia Lunar's bluetooth app for the first week, then I'd never use my phone to record any data.