DanoM Senior Member Joined: 20 Mar 2013 Posts: 158 Location: Los Angeles Expertise: I love coffee
Espresso: NS Oscar, '84 La Pavoni Pro,... Grinder: Baratza Vario, La Pavoni PGC
Posted Tue Apr 30, 2013, 10:17am Subject: Re: Coding a universal Arduino Coffee Control unit with pid
There's a Korean poster on YouTube that has a PWM for his vibe pump that seems to have good control. You'd likely have to test it in various environments, but I would guess you can dial in the pressure with this and have it be relatively stable for pressure? Of course an analog meter to keep an eye on things wouldn't hurt either. http://www.youtube.com/watch?v=2Ugl5pp5zaQ
What I would like to do is convert his PWM controller into using either a spring loaded slide rheostat or a 1/4 turn rheostat so that you could put a mini manual electro-lever on the machine for pulling shots. Pull down harder against a spring for more pressure, ease up for less, etc... Put in an analog pressure meter next to the lever and you'd have a very nice manual addon to that PWM system.
I did read somewhere that the Ulka pumps do tend to loose some flow as they age, so you might have to tune your PWM settings from time to time.
Ah... To have an endless supply of cash to spend on such mods! LOL
billc Senior Member Joined: 15 Jan 2009 Posts: 107 Location: Seattle, Washington Expertise: Professional
Espresso: CC1 - GS - GS3 - GB5 Grinder: Baratza - Mazzer-Marzocco Drip: My own Creation
Posted Tue May 7, 2013, 9:33pm Subject: Re: Coding a universal Arduino Coffee Control unit with pid
Ross, You can control the pump vis the controller. It is similar to PWM but not called PWM. Look up Phase control (phase fired control, signal chopping etc). Essentially to control the ac coil you still need to have something that is similar to an AC signal (60 hz that is). The way you control it is to delay the turn on time from when the voltage is at zero. To do this you must have something that senses the zero crossing of the AC voltage. Google it for more info.
You also need to have a type of relay that is a random fire type, meaning that it can turn on anywhere in the AC Wave. It is more typical to find a zero crossing SSR, meaning that it always turns on only when the voltage is zero.
joshblake Senior Member Joined: 6 Jun 2013 Posts: 1 Location: Toronto Expertise: I live coffee
Posted Thu Jun 6, 2013, 9:44pm Subject: Re: Coding a universal Arduino Coffee Control unit with pid
]Just came across this topic! I love the idea's here! I've actually already completed a lot of the feature-set that everyone is looking for including the AC-phase chopping to allow pressure control at the pump. Check it out: http://josh.to/crema. I'll be dropping the source code and hardware files under the Creative Commons Share-Alike Attribution license for anyone that's interested!
Regarding pressure transducers - I believe Auber Instruments sells them for a reasonable price that provides a ratiometric voltage output dependent upon the pressure Click Here (www.auberins.com).
I've been considering adding a 16-bit DAC to allow for a voltage dependent output to allow for Linear-Voltage-Dependent-SSRs as well as geared pumps (from Fluid-o-tech etc.). Although I have no immediate need for these features myself.
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