Arduino · Automation · Espresso · Gravimetric · Hack · pressure profiling · Zhng

Gravimetric espresso mod – project updates #2

It was almost a year ago when I made a post on the gravimetric espresso project. I promised to provide demo video and after a year of procrastination, here is it!

In this video you will find the following:

  1. How I use the OCD coffee distributor
  2. How I use The Force Tamper
  3. How to use the Coffee mobile app to set the target yield for gravimetric dosing
  4. How to use the smart scale
  5. How to use the coffee controller

How does the gravimetirc feature work?

Not much of the control logic for the gravimetirc feature has changed, it is already described in the previous blog post made a year ago here.

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The controller unit which connects to the relay and two flow sensors is now a simple wooden box. It has a display panel and button to un-lock the pump (de-activate the relay).


How does the auto shot-timer work?

Since the controller is connected to the flow sensors, the timer starts when water starts moving through the flow sensors. This is the same time the water starts saturating the dry espresso ground (pre-infusion if you like to call it). And in my opinion, this is the more accurate way of keeping time as compared to ‘first espresso drop’.

Why gravimetirc?

The benefits over volumetric and whats not are already described in the previous post. I believe that the automation will greatly reduce barista’s workload in slam-time. For me, it is so that I can focus on changing the brew pressure in-flight. You can see the pressure controller I have added into my machine here for ‘Pressure Profiling’. I shall make a separate post about that mod in future.


Is the gravimetirc mod reversible?

This mod requires 2 low-cost flow sensors to be placed in-line with the silicon water tube. The flow sensors can be removed and replaced with a 1/4″ water hose connector. The water hose can be replaced with a totally new one easily too.

The mod also requires the pump to be connected to relay. Since most of the actuators (pumps, solenoid) in the espresso machine are using spade connectors, it can easily be detached and attach to the relay, and it can be re-attached easily to the original configuration too. The following photo shows the pressure controller hooked up to the pump via the spade connectors.

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It is designed to sit even on the narrow drip tray that comes with Rocket Espresso machine. Here is the dimension!


Where are the buttons on the scale?

They are hidden too to maintain the minimalist and organic look of the scale. There are actually 2 touch sensitive buttons as shown here.


What is the scale made of?

I have explored a number of options and finally decided on a very simple design. These are real wood with weather resistant finishes. And I really like how organic they look.


This is one of the earlier prototype made out of bamboo coaster 😀


What about pour-over?

Oh yes, it has some really neat features for pour-over too. I am a home brewer too!


With the app, you can record your own or your favorite barista’s pour-over profile and use it to guide your next pour in real-time! The video demo is available here.

Does it work without the mobile app?

The mobile app is really for setting new target yield for gravimetric dosing and recording of extraction profile. The recorded flow-rate allows some form of channeling detection. I am using the gravimetric feature daily without the app, since I hardly need to change the target ratio.

Without the app, you can read the following information off the scale’s display panel.

  • Weight
  • Flow-rate
  • Timing

Is this a commercial post?

I have been building this mostly for fun with no profit, I might do a crowdfunding campaign to get initial fundings for mass production if there are enough interest. Please let me know if you find this project interesting? Meanwhile, stay tuned for the next updates!

Ending the post with a photo of my ‘work-shop’.





5 thoughts on “Gravimetric espresso mod – project updates #2

  1. Hey, really nice work! I love the clean design of the smart scales. I’m a fellow espresso machine hacker – send me an email if you’re interested in sharing notes.


  2. Hey, really nice work! Love the clean design of the scale. I’m a fellow espresso hacker, send me an email if you want to share notes, or just chat. Again, really nice work!


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