[SOLVED] Defeating microwave oven obnoxious beeping

[fzabkar]

Perhaps a warm female human voice that says something like, "Good morning, citizen, I've just nuked your breakfast".

Have we learned nothing from history/the future.Look at the chaos the talkie toaster caused

Wow, where can I get one? A real electronics geek should have a house full of customised appliances. Needless to say, I have an obligatory Big Mouth Billy Bass, and I've hacked the intro screen on both of my DVD players.

How about a cookie jar with a switch on the lid that triggers a warning from Southpark's Mr Mackie - "cookies are bad, mmkay".

Or what about a gadget that warns you when you're about to enter a toilet after someone has done a number 2? If you enter within a "smell delay", you hear the Lost In Space robot saying "danger Will Robinson, danger", or Kenny Loggins singing the "fly into the danger zone" theme from Top Gun.

[JustMeHere]

Have you tried pushing the off button before you open the door?

[Peabody]

Have you tried pushing the off button before you open the door?

Yes.  When the countdown has completed, the oven no longer recognizes a Stop key press.  So it just continues beeping.  And, actually, it won't recognize any keypress until it's finished beeping.  So it's absolutely relentless.  It demands that you listen to those five beeps and not do anything else.

But I am determined to defeat it.  I may break it in the process, but one way or another it's going to stop beeping at me like that.

And just to make it official, as Dave would say, Magic Chef = !!!!!!! FAIL !!!!!!!!!

[inse]

Thats what I call determination - GO FOR IT!

[black6host]

Well, from days of yore I'd try: Up Up Down Down Left Right Left Right B A and maybe START
  See if that works!    :-D



https://en.wikipedia.org/wiki/Konami_Code

[Peabody]

I've completed the circuit and the coding, and it works perfectly.  It detects when the countdown has reached one second, then "presses" the Stop button twice, which cancels the countdown and returns the microwave to idle.  Those presses produce two short beeps as an indicator that cooking is completed, but they are not obnoxious.

The protoboard is shown in the attached picture.  It includes an 8MHz Arduino Pro Mini, a TLC374 quad comparator acting as a level shifter, and an N-channel mosfet which shorts the row and column of the Stop button.  5V and ground are available on an ISP header on the microwave's controller board.  Inputs include the four digits' common anode pins.  Four of the segment lines are also inputs.  Since I only need to detect a blank digit, a zero and a one, only four segments are needed to identify those states to the exclusion of all other decimal values.  They are the A, B, D, and G segments.

The common anode lines are a bit of a puzzle because they swing through the full 5V, and because they are active low.  I suspect these inputs are actually the gate drives of P-channel mosfets powering the common anodes.

The oven powers the A, B, C and D segments one digit at a time, then goes back and drives the E, F and G segments in the same way.  So to get the currently  displayed value requires eight readings over a period of 10ms.  I'm still not clear why the designer did it this way, except possibly to reduce peak current draw since no more than four segments would ever be powered at the same time.

For the code I was going to use interrupts, but since the Pro Mini has nothing else to do, I decided to just process the pin values directly.  My code requires two successive readings of the one-second state over 20ms before it recognizes that state as valid.

This is a pretty elegant solution for me, and it took a bit of work to get right.  Particularly helpful were pictures taken at various shutter speeds revealing the two-stage display algorithm.  Anyway, it works like a charm.  So that's one minor daily annoyance removed from my life.

Netflix showed no interest in doing a documentary on this project.  Oh well.

Edit:  Details here:

https://github.com/gbhug5a/Microwave_Anti-Beep_Mod

[Peabody]

Forgot to say - the CPU on the oven's controller board had no markings.  So I don't think I would have been able to disassemble the code.

[inse]

Wow, that was incredibly fast.
What happens one minute after midnight?

[Peabody]

It's a 12-hour clock.  So one second after midnight, or noon, is 12:01.  The pattern I test for is "blank, zero, zero, one", which is what's showing at the end of a cooking or timer countdown.  In timekeeping mode, the ones digit of hours will never be zero unless the tens digit is 1.  And if the tens digit is blank, the ones digit will never be zero.  So I think it works right.

If it were a 24-hour clock, it might be necessary to keep track of the previous state, which would tell you if you're counting up or counting down.

It went pretty fast because I was able to use the parts I already had onhand, including the protoboard.  So I didn't have to order a board or buy any parts.  Both the circuit and the code are actually pretty simple.  What took the time was diagnosing how the microwave worked, which is still not totally clear, but clear enough.

[inse]

What took the time was diagnosing how the microwave worked, which is still not totally clear, but clear enough.

😆👍 I‘ll keep that as a quote

[Peabody]

I've posted the details in a Github repo in case anyone else wants to try something similar.

https://github.com/gbhug5a/Microwave_Anti-Beep_Mod