Timer activated by Reed on AC solenoid

MaxHeadRoom

Joined Jul 18, 2013
28,820
Although, it opens up a BIG can of worms. In order to replace those coils, you'd have to come up with a 24VDC source, then wire something up so that the 230V coil signals from the machine can control the 24V outputs (relays? AC input SSRs?) If you're designing your own system, it makes sense to spec the parts the way you want them, but adapting your coil preferences into an existing espresso machine that has all the wrong voltages and none of the right ones, plus no room under the hood for extra parts, would be difficult. And all that inside a machine where they're concerned about voiding the warranty...
Not if 240vdc coils are available.;)
Max.
 

Thread Starter

MelvinE

Joined Nov 14, 2018
10
I’ve been watching this conversation between you guys and it’s been very informative. Thank you.

As for the timer project: I’ve ordered attiny85 Microcontrollers and Honeywell ss495a Hall effect sensors. There’s some wait but I expect they’ll arrive beginning of next week. In the meantime I will study to learn more about these sensors. will post updates when I’ve made any progress.

Ebeowulf, thank you also for your insights and personal experience regarding scales. We have (semi-)reliable scales at all our venues. The problem is, though, that not everyone who works behind the machines is as involved with quality as we’d like, and it’s been my experience that often the weighing and timing is passed over due to this.

Our products are of high quality (we import and roast our own coffees), and it is my wish to make the measuring of parameters as easy as possible - hence these projects - so that even the least passionate and most lazy “baristas” will be able to serve high quality coffee.

We use Mazzers, on which one programs the grinding time. The point of my envisioned scale is that it will ultimately be connected to the grinder (I’m aware this will need to be “invasive”) so that it will stop the grinding process automatically at a set dose, rather than at a set time.
More clearly: I want to portafilter holder on the mazzers to be equipped with strain gauges, and then when the grind button is pressed, the scale will first reset to zero, then start the grinding process, and interrupt it when the desired dose is reached.

From what you tell me, this is far-fetched. You mention accuracy and durability as main obstacles. Could you elaborate? I’d imagine one would put the strain gauges somewhere where they cannot take any direct hits, and just calibrate them with a microcontroller. This may be incredibly naive, and if so, I’d like to know why.

Melvin
 

Thread Starter

MelvinE

Joined Nov 14, 2018
10
SS495a are linear output version, I would have though you needed one of the digital (on/off) version?
Max.
Thank you for pointing that out Max. I’ve ordered stuff before looking into it well because I’m impatient. Also, it’s difficult to get such electronic components over here in The Netherlands without paying stupidly high shipping prices, so I kinda ordered whatever I could find for a “reasonable” price (paid about 10usd for 2 of them, so still kinda expensive). I’m just eager to play around with the sensors and microcontroller. Will look into it more and order a digital version as well.
 

MaxHeadRoom

Joined Jul 18, 2013
28,820
Simulation shows that simply applying 230VAC through a bridge to a 230VAC rated solenoid results in much greater power being dissipated in the solenoid. It certainly wouldn't like that :eek:. The warranty would be voided.
It included the idea of changing out the coil to 240vdc!
Max.
 

Thread Starter

MelvinE

Joined Nov 14, 2018
10
Max, you are obviously experienced and knowledgeable. Would you care to offer some more of your time by commenting on the idea of a scale built into the coffee grinders?

EDIT: more specifically, on the feasibility of the idea.
 

MaxHeadRoom

Joined Jul 18, 2013
28,820
I haven't really had anything to do with that industry, but I would think it quite possible, Omega sell load cells but Very Pricey, there are some on ebay from China for a couple of dollars to experiment with, I would think that the application probably need the inclusion of a small microP of some kind.
Max.
 

Thread Starter

MelvinE

Joined Nov 14, 2018
10
There is a bi-polar, uni-polar and latch-unlatch by polarity reversal types.
Max.
From what I read there is also omnipolar, such as the Honeywell ss451a, and from what I understand, that would be perfect for my application.

The unipolar, bipolar, and latching ones, it seems to me, would all act the same, namely closing and opening the circuit (or turning on and off - I’m unsure about the correct wording) with the same frequency as the AC power supply switches direction, due to the magnetic field reversing polarity at that same frequency.
Whereas the omnipolar Hall effect sensor would remain “on” whenever the solenoid is activated, as it is indifferent to the polarity of the magnetic field, only turning “off” when there is no magnetic flux present at all.

Would you agree?
 

ebeowulf17

Joined Aug 12, 2014
3,307
SS495a are linear output version, I would have though you needed one of the digital (on/off) version?
Max.
Although, if the microcontroller they're paired with has a decent ADC, this might actually be better!

SS495 output accuracy is much better than the trip point accuracy on most hall effect switches I've researched. Several years ago I designed a non contact switching system with very precise trip points and no need for manual calibration, based on SS495 sensors and comparators. We've built thousands of them over the last few years and they're working perfectly, even in spite of a harsh, hot, humid environment. We couldn't have made the same system with any Hall switch or reed switch I could find because the tolerances on their trip points are too wide, so each unit would've required manual calibration.

So, I'm personally a big fan of the analog sensors, as long as you've got a comparator or ADC available to handle the analog signal.
 

MaxHeadRoom

Joined Jul 18, 2013
28,820
Bi-polar switch on whenever a pos or neg field is present, uni-polar only switch on one polarity, the latching switch on with one polarity, and switch off with the other.
Max.
 
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