Homemade Grinder Dosing Timer

Grinders are one of the keys to exceptional espresso. Discuss them here.
jlunavtgrad

#1: Post by jlunavtgrad »

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This little guy is the result of a few weekends worth of tinkering. The timer has a pair of relays that will run my coffee grinders for a programmable amount of time. I have a coffee grinder (Baratza Virtuoso) plugged in on the left, and an espresso grinder (Super Jolly) plugged in on the right.

The knob on the front is a rotary encoder, and it increments/decrements the time by 1/20th of a second (50 ms) per detent. Clicking the knob down toggles the grinder selection, indicated by the two amber LEDs on either side of the display.

The leftmost button activates pulse mode. In pulse mode, the grinder starts and the timer counts up from zero. Pulse mode is stopped when the button is released. The rightmost button activates countdown mode, where the grinder runs for the programmed amount of time. When the grinder is running pressing any button will stop the grinder immediately.

The whole thing is powered by an ATMEGA168, I wrote the code to drive the display, power the relays and read the inputs in C. It even saves the time values for both grinders in EEPROM so that you can power off the timer without losing your settings.

I'm a software engineer by trade, so actually building something with my hands was a lot of fun. I got a lot of practice with my soldering iron and the metal punch at work. I also spent a lot more time than I expected combing through the parts catalog on Digi-Key. But I am very pleased with the way the completed project turned out.

The timer has been on our kitchen counter for almost 2 years now and my wife and I use it every day. The timer has made brewing drip coffee simple and repeatable. It cuts out any waste from over grinding when making espresso, and allows me to get a more consistent dose than what I can do by leveling the portafilter with my lame Stockfleth skills :)

I have more pictures, schematics, the bill of materials and code I can share. If you are interested send me a PM.

jazz

#2: Post by jazz »

Very very nice! I wish I'd seen this some months back. I had a huge ugly dark room timer for my SJ, which took up way too much counterspace.

It's ended being one of the primary reasons I replaced the SJ with a Casadio Instanteano.

Nice work!

jlunavtgrad

#3: Post by jlunavtgrad »

Thanks Lars. Congratulations on your upgrade, the Instanteano looks like a neat grinder. I've had my eye on the K30 Vario for a long time. I built this timer hoping it would cure my upgraditis. It's mostly worked, mainly because I would not want to get rid of my cool little contraption.

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LaDan

#4: Post by LaDan »

I'm intrigued! What would that end up costing if I wanted to build it?

jlunavtgrad

#5: Post by jlunavtgrad »

The project costs depends on what you are starting with really. I had access to the tools to cut the aluminum through my old job, and I already had a soldering iron and prototyping PCBs. I would estimate that the parts cost about $70-$80 if I were to add them all up. The project box I used was the most expensive part at $10.15, even more if you count the bottle of Rustolium I painted it with (which I didn't include in the total). It seems like a lot, for such a simple device, but compare that to the price difference between a super-jolly and a super-jolly E which is more than $600!

Ben Z.

#6: Post by Ben Z. »

What do you have to do to the grinder itself to get it to work with your timer? Do you just rewire it so that the "start" contact on the switch is always on? Looks really nice!

jlunavtgrad

#7: Post by jlunavtgrad »

I didn't have to make any permanent changes to either grinder. Actually, I didn't even need to use tools. On my Supper Jolly all I had to do was pull off the plastic cover on the start switch. There is a rectangular piece of metal that slides over the shaft of the switch. This piece of metal is what the switch rests against when it is in the off position. I was able to flip that piece around so that the switch is held in the on position by the second screw. My super jolly is from the 80s, so I'm not sure if this would work on a newer one or not. My Virtuoso is a little more of a kluge. I pulled off the plastic cover to the timer switch and wrapped a fat rubber band around it and pushed it back in place. The rubber band gets squeezed against the timer switch and the grinder's housing and the friction prevents it from moving. Both grinders could be put back in their original position in less than a minute.

dustin360

#8: Post by dustin360 »

Its beautiful, great job!

dragonrider6218

#9: Post by dragonrider6218 »

This looks like a cool little project/add on. I have a rocky and would like to be able to have something like this for it. I am in to electronics and have already been putting together a list of stuff I would like to do in modding my Silvia and Rocky. This is sure to be one of the things I would do as time goes by.

JD1

#10: Post by JD1 »

This looks fantastic, and I would love to build one of these. PM sent! Thanks for sharing! 8)