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replacing Giotto controller with a DIY controller

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  • replacing Giotto controller with a DIY controller

    Hi all,

    it's been a while since I've been here. I've been plodding along fairly happy with my FZRR drum roaster; Gino Rossi grinder & ECM Giotto (2007) until the Giotto stopped heating a couple of weeks ago

    After some diagnosis I found that the water sensors, pressure sensor, element and pump are all ok, but the relay on the controller is 0xDEAD!

    I see some drop-in replacement controllers around $300 (I didn't think they made this one anymore so they must be an aftermarket compatible thing) but what I really want to do is replace it with my own design for a bit of fun and learning.

    I'm comfortable with the programming & purchasing side of things, but at this stage I'm not 100% sure how to use the existing water sensors. Has anyone tried this themselves? I may have to do some measurements.

    I'm not going to do any PID controlled solid-state relays or anything flash - maybe later. I'm just going to start with a like-for-like replacement. An Arduino with some extra bits n pieces would be sufficient. As far as I can tell, this is what it comes down to:

    Inputs:
    1. tank water sensor (need to put some voltage on a wire and detect an open circuit to ground to see if there is water)
    2. boiler water sensor (same as above)
    3. boiler pressure switch (just uses a microswitch)
    4. lever switch


    Outputs:
    1. Pump (looks like a 240V relay but not sure)
    2. Element (240V relay)
    3. maybe some sort of water valve to direct pump water to the boiler vs group - not sure yet


    There's also a bit of corrosion around some of the copper fittings, so I may end up taking the boiler out but we'll see.

    Well, what do you think? Anyone done this before who would care to comment?

    In the meantime, enjoy your nice coffee, cause I'm drinking from a moka pot!

  • #2
    Yeah, I've done it, they're pretty simple. My design is all analogue since I don't do digital, but the principles are the same.

    The water sensors are both run on comparators: You need a high value resistor between Vcc and the probe, then use the comparator with the voltage at this junction and a reference (eg Vcc/2) as its inputs.

    You do need a third output for the water solenoid.

    You do want to put an SSR in for the element, much better than an electromechanical relay. The pump and solenoid can be electromechanical relays, these are fairy low power. I use Omron G2R1A, available from RS for about $6 each, they mount on the panel and have standard 6mm spade connectors so they are very easy to use.

    Power requirements are another thing: it's easiest to run the relays etc on say 12V but you then need a lower voltage for Vdd for the uC (3.3V?). I find the easiest thing to do is to use a 12V regulated plugpack which I hack to take wired input instead of the 240V prongs. This can be made waterproof and tucked into the body of the machine, then you can just put a regulator on the board to provide Vdd.
    Last edited by Lyrebird; 30 June 2019, 06:36 PM.

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    • #3
      If you wanted a less exciting project you could always just replace the relay...

      If you are getting a SSR make sure to get one rated at twice the current it's switching.

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      • #4
        The element pulls around 5A. The common SSRs are 25A or 40A, so he's unlikely to get into trouble there.

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        • #5
          Originally posted by Lyrebird View Post
          The element pulls around 5A. The common SSRs are 25A or 40A, so he's unlikely to get into trouble there.
          Ok that's good, working in industry I'm always switching higher loads and upsizing to suit.

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          • #6
            Yeah the usual problem is that most things have a fairly positive temperature coefficient of resistance* so the current draw when cold is a lot higher than when hot: I use old transmitting triodes in one of my amps and they have a hot / cold ratio of about 10: 1, so I need current limiters on the inputs (also helps extend the life of these things which are now pretty well unobtainium).

            Old fashioned tungsten light bulbs were even worse, up to 15:1 which is why they just about always blew at turn on.

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            • #7
              Nice ideas, thanks.

              level3ninja where's the fun in just replacing the relay? Plus my soldering sucks and I'd have no excuse to play around!

              Yes a SSR would be good, but not yet as I'm not changing out the pressure switch just yet. Maybe later - I'll get it working first. Unless they're cheap and I can use it as a slow relay for now.

              You can get 3.3V triggered (or low triggered) relays and shields for the arduino, but I haven't seen any over 5A yet. I'll keep looking.

              thanks for the replies!

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              • #8
                Originally posted by iaindb View Post
                Nice ideas, thanks.

                level3ninja where's the fun in just replacing the relay? Plus my soldering sucks and I'd have no excuse to play around!

                Yes a SSR would be good, but not yet as I'm not changing out the pressure switch just yet. Maybe later - I'll get it working first. Unless they're cheap and I can use it as a slow relay for now.

                You can get 3.3V triggered (or low triggered) relays and shields for the arduino, but I haven't seen any over 5A yet. I'll keep looking.

                thanks for the replies!
                You could always get the small low volt coli arduino relay to control a larger relay.

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                • #9
                  Originally posted by fg1972 View Post
                  You could always get the small low volt coli arduino relay to control a larger relay.
                  I've never done a daisy-chained relay before - anyone done that and have advice to offer?

                  The existing relay is a jqx-115f - 16A.

                  It looks like some SSRs can be triggered at 3V and can switch large loads in smaller sizes, so maybe I'll use one of those anyway. I can only find this 40A model: https://www.sparkfun.com/products/13015. Lyrebird were you saying the cold current draw affects the relay or the element? Do I need to worry about soft startup or leakage current?

                  What about a MOSFET relay?

                  So many questions!
                  Last edited by iaindb; 8 July 2019, 10:03 PM. Reason: spelling

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                  • #10
                    For those following, I've ordered a Wemos D1 mini, as it has plenty of DIO, one analog input I can use later for the PID, and includes WiFi on-chip. It has relay shields, but I'll need a separate SSR for the element - probably a Fotek 25A or something like that - it will need to trigger off 3.3V. Just waiting on APost to deliver the parts!

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                    • #11
                      I have a similar issue, but my pressurestat runs ac to it. My SSR are DC triggered, so waiting for some ac-ac SSR to arrive.

                      But watching this to see where you end up...

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                      • #12
                        Originally posted by Jackster View Post
                        I have a similar issue, but my pressurestat runs ac to it. My SSR are DC triggered, so waiting for some ac-ac SSR to arrive.

                        But watching this to see where you end up...
                        You could probably rewire it, as I think this ac pressurestat was redesigned to use the same pressurestat as a dc input. From what I can gather the AC eventually burns out the pressurestat switch.

                        You can see the two different wiring options in this PDF: https://www.home-barista.com/downloa...E-13.03.09.pdf

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                        • #13
                          Originally posted by iaindb View Post
                          From what I can gather the AC eventually burns out the pressurestat switch.
                          That's more of a DC issue Iain.
                          Not so much with AC since at halfway through every cycle, the voltage is Zero....

                          Mal.

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                          • #14
                            Originally posted by iaindb View Post
                            You can see the two different wiring options in this PDF: https://www.home-barista.com/downloa...E-13.03.09.pdf
                            Or, maybe this one...
                            https://coffeesnobs.com.au/attachmen...a-part2of2.pdf

                            Mal.

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                            • #15
                              Thanks Mal, I happily defer to your expertise as I’ve seen inside a grand total of 1 of these machines!

                              So are you saying the DC pressurestat is a problem?

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