Haroldo Filho (who posted the "Espresso Preciso" video a few months ago) and I are working together to add weight-based coffee dosing as a feature to existing grinders.



Haroldo has his Android software working with his Mazzer Super Jolly, by cutting the power to the grinder using a bluetooth power switch, when the dose is at the weight you want it (using an Acaia scale). The Jolly grinds at a slow 2g/second, and this setup was quite accurate (about 0.2g accuracy average, 0.3g worse case).

I bought Haroldo a Mazzer Robur, but the super-fast 6g/second rate meant we had terrible accuracy. We needed to be able to pulse the Robur on demand. So... Haroldo opened up the Robur, wired in a lazybone bluetooth on/off directly into their wiring, so he can now pulse the Robur's motor from his Android software. There's enough space inside the Robur to hide all this.

He's running the motor full on until he gets within about 1g of the desired dose, and then pulses it to get to the finish line. What surprised me was how close he got in the end (worst=0.3g, average=0.14g). Here's a chart showing 64 grind tests:



and here's a video of Haroldo using the grinder/android software combination. If you have a slow grinder (2g/sec or slower), and enough space to stick an Acaia on a platform under your grinder's spout, the simple bluetooth-power-plug hack should work with your grinder.

I've also designed two 3D objects that I've locally printed to act as a portafilter stand on the scale and also an L bracket to replace your pf with a tray, in the cases where that's possible (it works well on my Super Caimano)



I wanted to talk about this prototype on HB, asked about doing so, and was told it was ok as long I as I included: "posted with permission from HB for feedback until commercially available".

At this point, this is just an R&D project I'm calling "Decent Doser".

Would love to talk, brainstorm, criticize, this idea...

Very clever and rather simple. Personally, the only thing that I don't like is the font chosen for the app. Looks rather 80's to me.

Absolutely, the app hasn't been prettified at all, it's just been coded to be functional. It'll get a prettier when we've decided it's as functional as it's going to get.

Would a revolution-based dosing system work better than time-based? A hall-effect sensor and a magnet attached to the motor fan could be used for revolution information.

Awesome, how much did the accuracy changes with different amount of bean on the hopper.
Also I'm curious about the Bluetooth interface to the acaia, do you have to reverse engineer the acaia app?

John, I think your idea has commercial potential (possibly great potential). If that interests you, I suggest you start talking to manufacturers before they produce their own versions. Since LM USA already has a relationship with Mazzer and Acaia, they might be a good place to start.

Bluecold wrote:Would a revolution-based dosing system work better than time-based? A hall-effect sensor and a magnet attached to the motor fan could be used for revolution information.

We're currently using a scale under the portafilter: that seems to me to be likely the most accurate way to measure the dose weight.

Marshall wrote:John, I think your idea has commercial potential (possibly great potential). If that interests you, I suggest you start talking to manufacturers before they produce their own versions. Since LM USA already has a relationship with Mazzer and Acaia, they might be a good place to start.

As it happens, I did talk to Scott and Joe at LM in Seattle about this last week, and both of them said they wanted one for their personal use, and possibly they might resell it in the USA, but for now that's it until I demo it for real to them (next month). I sent a ping to Mazzer on Friday asking for a conversation (pinged Mahlkonig too) and we'll see if I can get their interest. I don't think Baratza will be interested since they have their own weight-based dosing technology.

The Robur is pretty popular, but I would like to see this work too for HBs with their "consumer grade" grinders at a home-hobbiest-price, and then have a pro version, probably at this point a modded very popular pro grinder, which of course will be more expensive, since there's more work involved and well, we need to hack open a Robur (which isn't a cheap grinder!).

This plan kind of depends on whether Mazzer likes what we've done or sees it as a warranty-voiding abomination!

boost wrote:Awesome, how much did the accuracy changes with different amount of bean on the hopper.

Doesn't seem to effect it, since we keep the grinder on until we reach close-to-target, and then pulse. If your hopper isn't flowing right, it'll just take longer for this technique to get to your dose weight.

boost wrote:Also I'm curious about the Bluetooth interface to the acaia, do you have to reverse engineer the acaia app?

I have a copy of the old API from Acaia for the Lunar, that's how we managed it. However, Acaia have no currently-working API for the Pearl, and they're apparently locking down their API with encryption in the future, and only making it available under an NDA.

I should mention that I'm trying hard to get another 0.1 gram accurate bluetooth scale on the market, and am talking to a chinese scale manufacturer about customizing one of their models for us (they sell a 1 gram accurate bluetooth scale, and a 0.1 gram accurate non-bluetooth one). I'd like to get the price down to something like $80 for this, and have it be an open-to-hacking device.

I think the Acaia is an awesome scale, but their API policy, encryption and NDAs really go against my open source / open access view of the world, so while I'll support their scale if they'll let me, I don't want to be locked in by them.

Also, since we're working on a bluetooth controlled espresso machine, my plan is to use the same scale I'd have made for us to add gravimetric dosing capability to the espresso machine. I don't see why only the Black Eagle should have this really useful capability.

Love the idea and sign me up.

I didn't like the other timer systems due to the massive switch box I have seen posted. I would like the Bluetooth switch to be contained within the grinder so it doesn't take up counter space.

jwCrema wrote:I didn't like the other timer systems due to the massive switch box I have seen posted. I would like the Bluetooth switch to be contained within the grinder so it doesn't take up counter space.

If you have a slower grinder (2g/second) than there's no need to bluetooth enable the grinder by hacking into the wiring. We have a bluetooth power switch, that plugs into the wall, that turns the power off on the grinder when the dose is reached.

Here's a photo of my setup with my Super Caimano grinder.

In order for this hack to work, you do need to get a scale in under the spout, and a scale-compatible stand too for the pf to sit on. Haroldo uses a bottomless portafilter, so his stand is very low profile, while I use a double-spout LM pf, so I designed a tall pf stand on top of the scale. The pf stand in this photo is for my setup. I'm still tweaking the pf stand design, as it's difficult to make it work for all kinds of different shaped pfs. I do plan to make them out of silicone, though, so that the pf doesn't slide on the stand.

To keep it open source have you considered making your own scale with a load cell and a microcontroller to read the output and send the info via bluetooth? I'm using a load cell out of a cheap 0.1g accurate scale here with an arduino and OLED display, instead of wireless. May be able to achieve your price point if you go this route.