The kettle, spark core, relay

Hi! I'm still working on my kettle project. I want to obtain the kettle temp from the existing thermometer. I'm able to do this, but much like trying to look at an electron my circuits all reduce the voltage going to the kettle control board. This means the kettle's microcontroller (SN8P2722 SONiX) acts as if the kettle is cooler than it really is.

5v control board.

I don't think there is an easy way to program this microcontroller (if there is I'd love to know) -- I suspect the bad temp data will lead to overheating and hot water all over my kitchen.

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Is there any way to passively obtain the voltage? I've been looking into the way that voltmeters work. Is this the right idea? is there a breakout board for this?

I really wanted to have the existing buttons still work as they always have. I've done this with power. I can press it remotely or on the kettle and I can tell of the kettle is on or off both on the control panel and remotely.

enter image description here

I can press all the other buttons remotely but I can't tell if it's working without knowing the kettle temp.

Maybe I should try to replace the entire control board? What would be easier? I'm something of a beginner.

  • 1
    Please post the schematic for the voltage-measuring (temperature measuring) part of your system. The input impedance of the analogRead should be pretty high.
    – Nick Gammon
    Jul 13, 2015 at 20:51
  • 1
    I'm the last person to question somebody who's making a tea-related project, but are you ultimately attempting to control your kettle over WiFi? Do you really need to be able to turn your kettle on from your computer or phone so that it's just boiling as you walk into the kitchen and thus eliminate all that unnecessary hanging around while OH MY WORD THIS IDEA IS GENIUS. Jul 13, 2015 at 22:25
  • This means the kettle's microcontroller acts as if the kettle is cooler than it really is. So what? Just "press" the button again to turn it off when you determine empirically that you have reached the right temperature.
    – Nick Gammon
    Jul 13, 2015 at 22:43
  • I can press all the other buttons remotely but I can't tell if it's working without knowing the kettle temp. Why wouldn't it work? You have pressed the button, you detected the "on" LED lit up. What could go wrong now?
    – Nick Gammon
    Jul 13, 2015 at 22:46
  • Where are you attaching the wire going into the analog pin on the arduino? There might be some amplification/buffering going on on the board. Try tracing where the signal goes, and then connect the wire to the trace that's going strait into the microcontroller. Also, do you have any idea what kind of sensor they use for temperature measurement?
    – Gerben
    Jul 14, 2015 at 12:40

1 Answer 1


A JFET op amp such as the TL071 has an input impedance in the hundreds of gigaohms or higher. Using one to buffer the voltage should allow you to sample it without much interference to the existing circuit.

  • so the goal is to make this: en.wikipedia.org/wiki/Precision_rectifier
    – futurebird
    Jul 13, 2015 at 16:52
  • Why do you need to rectify the signal? Jul 13, 2015 at 16:53
  • "Total Supply Voltage (Min) (+5V=5, +/-5V=10)" the voltage is 0-5v. This is less than the min? I can look for one with a different set of specs.
    – futurebird
    Jul 13, 2015 at 16:54
  • I just need to read about this more. I'm really confused.
    – futurebird
    Jul 13, 2015 at 16:55
  • A circuit diagram would help muchly. However: the analog voltages are most likely DC. If they are within Arduino ADC range then reading most such would affect them minimally. If a buffer is needed then a circuit as simple as in Fig 3 in Ignacio's buffere reference should be good enoug in may cases - but a TL071 may not be the best choice, depending on voltage to be measured and available supply voltages. | Using a voltmeter (DMM) will allow you to measure voltage and advise us how it varies with temperature. ... Jul 13, 2015 at 17:33

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