Read an analog signal without changing it? Or should I start over? 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. 



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. 



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. 



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.
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.