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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 260
Location: Americas
Expertise: I like coffee
Posted Mon Aug 5, 2013, 1:10pm
Subject: Computer controlled temp and flow profiling
 

I installed a small computer (aka micro-controller) to control boiler temperature (and ultimately the pump, which enabled pre-infusion and flow profiling) on my Gaggia Classic (although much of this applies to many other machines).  I used a FreeScale FRDM-KL25Z for the computer.  It's only $12.95 and has more features and better A/D accuracy than an Arduino.  Other parts are:

Solid state relay (SSR-40DA),  $8
PT1000 RTD bare temperature sensor (low mass, it responds quickly),  $4
2.2K ohm precision resistor, $2
thermally conductive epoxy (to attach the sensor to the boiler)

Optional:
some firestop foam (to keep ambient air from influencing the sensor)
IGBT for high speed PWM/voltage pump control, (ISL9V3040P3), $2
2 kickback diodes (1N4007-T), $1
DS1307 real-time clock board for auto turn on, $2
Another PT1000 RTD for logging thermofilter temp, $4
Load cell (scale) for real-time measurement of flow, $10

Prior to preheat/brew, this controller uses pretty conventional closed loop (similar to but not actually PID) temp control.   When you are ready to brew, you press a button and the computer starts ignoring the temperature sensor and does open loop PWM control of the heater.  The % power levels are taken from a table and you can put a different value into the table for each second of the preheat/brew cycle.  At the 10 second point, the computer turns on a LED to indicate that the pump should be started.  While I'm getting very good results, I haven't determined exactly what values should be in the table.  Calculations tell me that a Gaggia Classic could need as much as 65% of full heater output to keep up with the cooling effect of incoming water during a typical shot.   The exact timing and power levels for preheat are less clear.  Based on values others have used for manual temperature surfing, 4 seconds of 100% and then 4 seconds of 0% is my starting point.

I added automatic turn off after 1 hour of inactivity (saves me about $50/year or is more convenient) and some error checking - if the A/D value is outside of reasonable values, it shuts down.  The computer has a multi-color LED to indicate status (heating, brewing, sleep mode, etc).  I have not yet made a box for the computer board - it's sitting on the counter.  I will have graphs of brew basket temperature vs time to show the resulting temp profiles.

The wiring was simple and the software is available.  If you are considering adding a PID controller, consider this instead.  You do lose the temp readout that typical PID controllers have and to change the temperatures, you need to connect your PC and change the program.   On the other hand, this mod allows flexible preheat and brew temp profiles and allows changing the program to do additional things.   The Classic wasn't permanently modified - everything could be put back to stock in one minute.
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DanoM
Senior Member


Joined: 20 Mar 2013
Posts: 217
Location: Los Angeles
Expertise: I love coffee

Espresso: NS Oscar, '84 La Pavoni Pro,...
Grinder: Baratza Vario, La Pavoni PGC
Posted Mon Aug 5, 2013, 3:56pm
Subject: Re: Computer controlled boiler temp - better than PID
 

Nice mod there.  Would like to see some photos of the setup.

User daduck748 built an external housing case on the front to hold his computer module along with some push button input and display that looks quite nice, but then again he's got a shop full of machining tools to make whatever he can imagine.  (I noticed you've been on his thread, so no intro needed there.)
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 260
Location: Americas
Expertise: I like coffee
Posted Mon Aug 5, 2013, 5:17pm
Subject: Re: Computer controlled boiler temp - better than PID
 

daduck748 is my primary inspiration (thanks!) and anyone interested should definitely read his topic:

Click Here (coffeegeek.com)
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calblacksmith
Moderator
calblacksmith
Joined: 25 Nov 2007
Posts: 7,479
Location: Riverside, Ca, U.S.A.
Expertise: I live coffee

Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Tue Aug 6, 2013, 6:18am
Subject: Re: Computer controlled boiler temp - better than PID
 

If your setup makes you happy, good for you and may you long enjoy it.

I have a different point of view on a few things. First, the water in the boiler will be less stable than the shell of the boiler, the shell acts like a heat sink and is slow to respond to the changes going on with the water inside the boiler, you will always lag what the water is doing. It may not be enough of a difference that you can taste it ? YMMV.

Next, many PID units can operate in an off/on mode, like a very accurate thermostat and do not pulse the power to ease to the required temp. My personal view is that the PID is more stable but again, YMMV.

and last but not least, a PID is much smaller than a computer and can be built in, thus making for a cleaner installation, however "cleaner" is in the eye of the beholder YMMV!

There is nothing wrong with what you did and if you enjoy it GREAT!, ENJOY!

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 260
Location: Americas
Expertise: I like coffee
Posted Tue Aug 6, 2013, 7:01am
Subject: Re: Computer controlled boiler temp - better than PID
 

> the water in the boiler will be less stable than the shell of the boiler

Before brew, the shell is the only thing that influences the water temperature.  So it's always less stable.  That's why the original thermostat could have 50F of hysteresis and still produce decent espresso - the water didn't vary that much.
Click Here (www.home-barista.com)

During brew, incoming water is creating the instability and yes, the shell temperature is misleadingly stable and/or inaccurate.  That's why I ignore the shell temperature during brew.

The computer board I'm using is just slightly larger than the PID unit I have.  But with any electronics, I'm hesitant to build it in because of heat.  But I did put the SSR inside for electrical safety reasons.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,881
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Preciso
Posted Tue Aug 6, 2013, 9:59am
Subject: Re: Computer controlled boiler temp - better than PID
 

jonr Said:

> the water in the boiler will be less stable than the shell of the boiler

Before brew, the shell is the only thing that influences the water temperature.  So it's always less stable.  .

Posted August 6, 2013 link

jonr Said:

I installed a computer to control boiler temperature on my Gaggia Classic (although all of this applies to most other machines).  

Posted August 5, 2013 link

Perhaps the confusion about what is most stable, boiler or water depends on machine, or where the heater is - internal to the boiler tank or in the wall, and the statement about Gaggia, then applied to most other machines.
 
  Just a note, I could not click on the HB link above.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 260
Location: Americas
Expertise: I like coffee
Posted Tue Aug 6, 2013, 10:29am
Subject: Re: Computer controlled boiler temp - better than PID
 

Good point - the Gaggia has the heater coils embedded in the shell, not in the water.   With other boiler designs, I agree, the shell is going to slightly lag the water temperature and this would increase the importance of some type of learned power level.  Enough to worry about - I don't know.  I should probably just add the few lines of code needed to accommodate this (ie, learn the exact heat needed to maintain idle, similar to PID).   OK, done (10 more lines).  It's controlling temp boiler wall temp to .15 degree.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,881
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Preciso
Posted Tue Aug 6, 2013, 4:26pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

Jonr, please take this as an opportunity to further explain your system.  I do not yet see “Better than a PID.”  Perhaps it should be better than a PID??, or alternative to a PID, or perhaps better than Arduino? And no, I am not saying a PID is better.

You noted better A/D, but has that been a problem on Gaggia, or Arduino?  Is temperature control needed that exacting?

Automatic turn off is nice, but with a PID, I wonder what would happen if left on and the boiler ran dry.  I do not wonder enough to try it, but the PID may solve that.  But I have not left it on, nor do I read of that being a frequent problem.

jonr Said:

 If you are considering adding a PID controller, consider this instead.  You do lose the temp readout that typical PID controllers have and to change the temperatures, you need to connect your PC and change the program.   On the other hand, this mod allows flexible preheat and brew temp control and allows changing the program to do additional things.   The Classic wasn't permanently modified - everything could be put back to stock in one minute.

Posted August 5, 2013 link

PID is simple for the user to install reversibly, probably similar.  No computer hook up needed, changes are easy, and temperature displayed.  Are you meaning tighter control, or flatter temperature profile? Actually there is some discussion about how flat of a temperature is desired.

I do like the feature, if I understand, that you hit one button that adds a blip of heat, then rest, and then starts the brew as opposed to me hitting the steam switch and then off, and then starting the brew.  I thought of trying that with ramp soak on PID, but then decided to keep it simple, for myself and any who might wish to add a PID.

As noted, this is an opportunity to expand your topic into more explanation, and hopefully it is not offensive, for those who would consider a PID and then see “better than a PID.”  Also you might talk a bit about setting up the software what is needed besides the board.  I looked at the FreeScale site and did not find it intuitive.  I did not know the term PID until I started about 1 year ago, but found PID information easy to understand.

I am happy to see you at the building stage.  I think that temperature control for brew, intrashot, and steam are fairly easily done with a PID.  I would like to have the ability to cool the boiler after steam and have temperature stability quickly.  The remaining downside of Gaggia SBDU is steam back to brew.  Perhaps “better than PID” controllers could use tank water temperature, volume needed to refill the boiler, and then calculate that fill and possibly extra flush to approximate the amount of water calories to rapidly stabilize the boiler back at brew.  If water needed to fill is already more than needed to cool, then heat could be calculated and added.  The solution may be more outside the box, but I hope that it does not destroy the simplicity or cost of the Gaggia SBDU.  To me, the upside is the small boiler, often quoted as a problem, but useful especially with heaters out of the boiler internal.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 260
Location: Americas
Expertise: I like coffee
Posted Tue Aug 6, 2013, 6:45pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

It goes without saying that better is subjective.   The primary advantage of this over the typical off the shelf PID controller is automated and user settable second by second control of heat applied just prior to and during brew.  You should be able to make a flat temp vs time profile, or rising, falling, double hump, whatever you want.   That's better to me (and La Marzocco :-)), but I suppose some might be completely satisfied with the profile they have.   Large boilers certainly have flatter profiles than a small Gaggia.  Let me know if this key feature isn't clear.  

IMO, the remaining things are relatively minor:

I was all set to use an Arduino, but the limited range of the A/D converter would have required additional circuitry (for gain and offset, as others have done).  This is a cost/complexity issue.

For me, auto turn off is an energy saving/convenience feature.  I'll probably add "automatic on in the morning" too since that saves me using a wall plug timer or waiting for warmup.

I deal with all kinds of small computers frequently, so I'm not typical.  But I find reading and changing commented code much easier than deciphering and programming a PID controller with the few buttons on the front and then wondering why it didn't do quite what I wanted.  It's a closed "black box" with limited, generic (not espresso machine specific) features.  A good intro to using the computer board is here http://mbed.org/getting-started/ and of course anyone else only has to paste in my code, not write it.   I'm available to help if needed.  When a laptop is attached (normally not needed), the software prints out various status information so it's easy to figure out what is happening.  

I've left steam unmodified although it would be easy to control the heater for that too.  Or add another SSR to be able to control the pump for pressure profiles or as you say, rapid cool down (steam back to brew).   Such flexibility is better for anyone who likes to experiment.

I didn't want to get into making changes to the hardware - ie, cutting tubing and wires, holes in the case, etc.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,881
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Preciso
Posted Tue Aug 6, 2013, 7:56pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

I believe that you know from my PID thread that adding heat during the brew can also be done by the PID, and the intrashot stability is reasonable.

http://coffeegeek.com/forums/espresso/machinemods/571792

You have automated the steam switch flip at the beginning of the brew as I thought about with ramp soak, I believe still PID able.  I did not find the just right PID controller with the alarm functions exactly the way I wanted, plus ramp soak.  I like your automation.

The other feature that I would like automated is the amount of heat added in relationship to shot size/weight.  I have to change parameters if I significantly change shot size as heat matches water through the boiler, out for the shot.  Do you see automation there?

Have you measures temperature out the group or into the PF?  I am sure that you will not have a problem other than adjustment.  AndyPanda got good temperatures, measured and on video noted in the thread above, by learning good surfing.

ShortyJacobs also did well, on a PID thread, with PWM control of intrashot, so it all works.  I know that you are aware of that also.

http://coffeegeek.com/forums/espresso/machinemods/611316

 
D4F also at
http://www.gaggiausersgroup.com/
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