bidoowee wrote:Ha - (at the risk of going mildly off topic) I suppose there are worse programs out there, but this is a commercial product and I expect better.

You obviously have more experience with CAD programs than I do. Never missed that stuff because I've never used anything that had it. And I guess I never expected much for the price when I started. Maybe now that Autocad bought it and charges per year there will be enough money and direction to move forward.

Ira

Hello there,

first of all let me congratulate you for the awesome work you're sharing with us in this thread.
I'm honestly blown away, and can only dream of being able to do half of what you did (the group is a beauty BTW). I'll be sure to keep an eye on your project

I have a question regarding the electronics:

bidoowee wrote: Someone requested an explanation of the autofill circuit. What is required is essentially a comparator - a circuit that checks to see if a voltage level is above or below a certain threshold. The essence of the circuit is a switch that is grounded by the water when it touches the probe.

I've been tinkering with micro-controllers inside coffee machines lately, and also tried to go this way for the auto fill.
But after doing dome readings I realized it might not be such a great idea because of electrolysis. And 5V DC does that to a metal probe in water.

How did you solve it? IIUC, going below 1V prevents it but then the reading can become less reliable.
Maybe it's not that much of a problem TBH, but those concerns led me to go for a very simple GICAR (Might be wrong but I believe they use AC) rather than an Arduino.

Cheers,

François.

Edit: spelling...

Conceptually if you're designing the electronics from scratch, you should only need to check the water level very occasionally.

Right before turning on the heater.
While the heater is on every few seconds
While the pump is running, a few times a second.
The rest of the time, there is no reason I can think of to check the level.

I think Gicar might use a free running oscillator that dramatically changes frequency when the connection to ground is removed, but I've never put a scope on mine to see.

Ira

ira wrote:Conceptually if you're designing the electronics from scratch, you should only need to check the water level very occasionally.

Indeed, so I guess the question then becomes "how occasional should it be to prevent electrolysis?"
(I read that people developing water sensors for plants end-up with the problem if they don't use capacitive sensing, and they probe every hour)

https://waterlevelcircuit.blogspot.fr/2 ... level.html shows a solution which might be viable, but the statement "Highly sensitive, so even a dampness on the surface where the sensors are placed may cause error sensing" at the end isn't reassuring... Maybe by having the probe inside a teflon tube, so that only the tip is exposed inside the boiler?

François.

Good idea on the Teflon coating; The Gicar controllers that I have seen on machines that I have renewed all used a blue vinyl/epoxy coated lead so only the end of the conductor is exposed.
Other sensor firms do also. The part should be available from a machine repair facility/ supplier.
~espressme

francois wrote: I've been tinkering with micro-controllers inside coffee machines lately, and also tried to go this way for the auto fill.
But after doing dome readings I realized it might not be such a great idea because of electrolysis. And 5V DC does that to a metal probe in water.

Thanks for your kind words François.

I think you may be correct about electrolysis. It is an interesting question and I actually hadn't thought about it. When I repaired the GICAR in my machine, I looked fairly closely at the circuit. I took a few notes, but I didn't draw it completely. Looking back at the notes, what I did see was an AC transformer with two taps, marked as 15V and the other for 20V (these measured 19 and 27 VAC (with no load)). I'm pretty sure that the probe was connected after a rectifier and that a capacitor was used to provide hysteresis. I therefore assumed that there was a constant DC voltage going to the probe. However, I just took the cover off my machine at home and put a multi-meter on the probe. The readings are not conclusive. I see roughly +160mV which seems to drop occasionally, possibly below zero. I don't see AC, but this is on a 200V scale with a cheap digital meter... I'll bring home a better meter this evening. It seems pretty unlikely that there is 19V or 27V AC present though.

I've not been able to find a circuit diagram of a GICAR. If anyone has one, please do share!

ira - This is an HX design, so there are the only two draws on the boiler: the HW tap and the steam valve. The current code samples the probe once per second as there is no way to know if water has been taken from the boiler. The long sample time provides the necessary hysteresis. There is also a timer on the fill solenoid that shuts everything off and waits for a manual reset if it runs for too long.

Here are the photos of the GICAR controller that I took way back when:

Hello:

First let me say that I am absolutely amazed both at your knowledge and expertise and how you have been bringing this project along.
On a side note, I'm also terribly envious of the tools and facilities you have at your disposal. =-D!
I have to travel a couple of hours (and plead for shop time) to get a shop that will do the dumbest things on a lathe or some simple SS welding.

bidoowee wrote: ... a circuit diagram of a GICAR. If anyone has one, please do share!

Here's what I put together some time ago when the Gicar in my Cimbali Junior (controls boiler level and doser/doser level reservoir) and started to act up. It's not precisely a circuit diagram but it may help you along.



Congratulations on your fabulous project.

Cheers,

CIV

bidoowee wrote:When I repaired the GICAR in my machine, I looked fairly closely at the circuit. I took a few notes, but I didn't draw it completely. Looking back at the notes, what I did see was an AC transformer with two taps, marked as 15V and the other for 20V (these measured 19 and 27 VAC (with no load)). I'm pretty sure that the probe was connected after a rectifier and that a capacitor was used to provide hysteresis. I therefore assumed that there was a constant DC voltage going to the probe. However, I just took the cover off my machine at home and put a multi-meter on the probe. The readings are not conclusive. I see roughly +160mV which seems to drop occasionally, possibly below zero. I don't see AC, but this is on a 200V scale with a cheap digital meter... I'll bring home a better meter this evening. It seems pretty unlikely that there is 19V or 27V AC present though.

I've not been able to find a circuit diagram of a GICAR. If anyone has one, please do share!

I've been looking for some more details on those as well, but I'm affraid my Google-fu isn't good enough to find detailed resources about GICAR.
Still, the Astoria SAE Junior (CMA/Laurentis/RIO) Refurbish Log thread is interesting:

Billc wrote: The only function for the RL30 is autofill for the boiler (turns on pump and valve). The RL30 is really a capacitance sensor similar to a touch screen. The probe is one end of the sensor and the ground is the reference. So if there is a disturbance, like water touching the probe and connecting the probe to the reference then the capacitance circuit, though a bit more complicated, activates a transistor that in turn allows current to flow to the relay that activates the pump and fill valve.

Wouldn't this explain why you couldn't get a reading with the multi-meter?

I never looked really hard into the difficulties of implementing such a probe with an Arduino, but assuming this is the solution it shouldn't add much complexity to the overall design.
But for some reason I'd tend to favor GICAR-like, old-school electronics for such a critical function. If it breaks, the machine can't heat. Or something like that

Cheers,

François.

civ wrote:Hello:

First let me say that I am absolutely amazed both at your knowledge and expertise and how you have been bringing this project along.
On a side note, I'm also terribly envious of the tools and facilities you have at your disposal. =-D!

CIV

Lol. Thank you civ! I am lucky indeed to have my shop (you can never have too many tools).

François - It would indeed seem that there is something slightly more complicated going on here than I first thought. The "less than one volt" chimes with the readings I was getting yesterday. I completely agree with you about using "old-school" electronics techniques - they tend to be designed by "old-school" engineers for longevity, simplicity and robustness. The Astoria link is a good clue, (if a little nebulous) as is the "electrolysis-free" water level sensor link - though that one is conveniently missing the actual circuit diagram. As I write this, the machine with the GICAR is cooling off. I'm going to extract the controller and take it to the shop for another look.