Understood. What you're talking about now is the quality of a lever machine produced and managed by an automatic machine. In that case, a 1-second sample interval is probably not going to be enough for what you're thinking about. Granted, that's 25-30 samples and adjustments per shot, which would probably produce better espresso, but if you're talking about optimized, you will need something a bit more powerful than an Arduino, like a Raspberry Pi or a Cortex. Anything more than this is probably going to be overkill... for most of us anyway. You would probably need a lot more memory in that chip for the program(s)/subroutines than an Arduino can offer. My PIDuino et all the managing software components are almost at the memory limit so my next thing to to either up the PIDuino to the next level processor or break it out into dedicated sub-modules, all communicating over I2C. But available time is not looking good for me.
So, implementing an on-the-fly OPV (what I've designed, not built), an on-the-fly OPV controlled by microcontroller, and an implementation for pressure profiling are three different things.
An on-the-fly OPV is a step up from what Gaggia provides out of the box. My design makes it two steps up from there, since it is placed before the pre-heater (for me). I will be able to adjust the OPV with the top off and all tubing uninterrupted.
A microcontroller adjusted unit is exactly how I described previously. Perhaps there are other ideas, methods, approaches... whatever. I know there are plenty of smart and creative people here. That's just how I would do it, the brute-force, direct way, throw-some-hardware-at-it way.
Now for pressure profiling, it starts to get more complicated because you have to implement the second idea, plus management software. Like I said, now you have to "UP" your processor, most likely DSP programming (?), C++ instead of the easy Arduino IDE programming (which is based on C, but a whole lot easier), and/or learning Linux to throw on the Raspberry Pi.
Also, I don't remember but I don't think you're building a Gaggia Classic, right? Well, I know the GC has a very small boiler, so out-of-the-box, there is plenty of room under the hood. But that room is not optimal for large chucks of technology. My boiler has grown, since I installed the pre-heater so the head-space is just about filled. In the back side, the funnel takes up a lot of room, since the empty space around it is pretty useless. On the side of the funnel is where the stock pump goes, which my new motor is roughly the same size as the stock pump. Then I add my new pump cap with OPV, which is a fairly large chunk of aluminum (brass is too expensive, especially getting large chunks like that). There is definitely no space for a NEMA23 servo (servo is probably the easiest to implement for this) which is about maybe 12 cubic inches. A NEMA17 servo is roughly 8 cubic inches but that's going to be TIGHT! Some folks may just do away with the funnel and fill the tank directly. I have the Rancilio Silvia V3 steam wand mod on my GC and I had to modify my tank so I could remove it... and it's still not easy, so I'm keeping my funnel intact, which leaves me practically no more space. It's like living on a boat; something comes on, something else has to go.
That's the technology part of it. Now comes the art and skill of Espresso. For years, I was an "occasional" or "social" coffee drinker. I didn't know anything about coffee... and I think I still don't know anything about coffee. Of course, everyone starts at Starbucks... and I had NO CLUE what to order... I still have no clue what to order at SB. Long story short... I got into Espresso because I'm opening a cafe in CA (the Health Department is FINALLY inspecting the drawings and premise... it's been a GRUELING process and wait!) and I had to learn all I could learn about coffee. My skill is now pretty decent. Everyone who has tried my espresso tells me it's awesome. Now, if they are JUST BEING NICE is really going to hurt me... and my business so I hope they are not JUST SAYING THAT. But I believe anyone in the coffee forums and making mods is already making better coffee/espresso than SB or the like. However, I'll go out on a limb here and say, probably not 50% of the folks here have a palette that could identify how good espresso from a lever machine tastes, or have ever had espresso from a lever machine. Have you? I'm not being condescending, just asking because whatever pressure profiling mechanism you want to implement will be based on your experience with lever machine espresso. After you've implemented it, how do you compare your implementation with the results from a lever machine. Maybe you have a lever machine and you get great espresso from it. I wouldn't know.
I have had espresso from a lever machine, just once. It was DELICIOUS! I had it pulled when I was at CoffeeFest a few years back as I was tasting and looking for a roaster. It's a shame. I was so excited that I forgot the name of the roaster. But they cheated by using a lever machine. It was the BEST I had. I even took two drinks back to my hotel room. But could I reproduce this? Probably not. I only had it once. And a lever machine costs WAY too much to invest in one.
I just invested in an old 95 Jeep Wrangler that I'm restoring. That takes most of my off-time these days. :D
MJW Senior Member Joined: 25 Jul 2012 Posts: 179 Location: Silicon Valley Expertise: I love coffee
Posted Sat Sep 21, 2013, 2:16am Subject: Re: Custom Thermocouple for Gaggia Classic
You guys are a lot of fun to follow. On the subject of "anything is possible", there is another way to eliminate a sensor, which is to watch the effect of the unknown variable on other sensors.
For example it might be useful to know or guess approximately the temperature of the incoming water. It might be well water, very cold, or it might be from the tap, and relatively warm. Knowing or estimating this variable might help accuratize the estimate for how to drive the heater during a pull.
Instead of putting a sensor on the input, the machine could, as it is used watch what happens to wall temp, when the pump is on, and calculate an estimate of the incoming water temp based on change in wall temp. (You would have figured out what the calculation is, using a sensor during development of course.)
Another idea I like is having a machine that learns what ToD and DoW it is likely to be used. The device logs all use by the hour and DoW, and gradually learns it is used afternoons and evenings but not on Tuesdays. It then sets the boiler temperature according to the intensity of its belief that it is about to be used. You still have to press a button to wake it up but wait time is reduced. Reduces energy use, and scale buildup! So many advantages...
jonr Senior Member Joined: 25 Jun 2013 Posts: 295 Location: Americas Expertise: I like coffee
Posted Sat Sep 21, 2013, 7:21am Subject: Re: Custom Thermocouple for Gaggia Classic
> For example it might be useful to know or guess approximately the temperature of the incoming water.
I measure the boiler temp when the machine is first turned on and if it appears to be a reasonable room temperature, I use it as the reservoir water temperature and it creates a minor adjustment to heat added during brew. But I haven't looked at how much reservoir temp rises as the machine warms up - a good algorithm may have to account for that too.
> that a falling temperature is not hiding flaws in the coffee that the flat curve is letting through?
I don't worry about the semantics (hiding flaws/releasing more flavors?) , I just look for better taste.
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