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The Ideal Microwave Keypad (and operation)

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Hi,

I meant you can use ice and boiling water as two test points, and room temperature as the third in the middle. This allows you to get three readings for the calculation.

Yes thermistors are non linear, but they are somewhat linearized quite easily over a smaller range, and using them for temperature setting (rather than measurement) using analog comparator techniques takes the non linearity right out of them. So the inherent non linearity would not bother me in the least :)
Using a microcontroller also makes short work of the linearization too if that's what you prefer.
 
... And the more i think about it the more i see that it could be quite easy electrically, as i could get away with an interface for only that one button.
...

Looks like you are simplfying the soltuion! It get a lot easier now, all you need is to tap into those two wires in
the oven's keypad matrix and add some sort of SPST switch, either a small relay or an analog switch like a 4066. That's the only interface needed into the MWO, everything else is your choice.

You could add a row of buttons, one for each heat. Then press the correct heat button and press "go" on the MWO.

...
But it will be fun trying to get the actuator to do the work at first, just to see how it goes. I'd like to see how fast i can get this particular actuator to go in an out too just as a test.
...

You need a lab coat, crazy hair and a maniacal laugh to complete this project I think... And maybe some thunder and lightning in the background on the night when you finally plug it in to test it! :D

Seriously now, the speed issue will likely be caused by the software debouncing in the MWO micro. They normally only allow slow presses. You could try pressing it really fast with your finger to test?
 
Hi MrRB,


Ha ha, did i forget to mention that the antenna on the roof is there to collect lightning to power the actuator?

Yes i tested it with finger, and it can go much faster when i press it really fast several times (originally i thought that would not work), but it's not something i want to have to do every day. Holding the button in makes it decrement quite slowly so that's not a good option. As you said, a single external keypad with ten buttons should do it. There would be a small delay after pressing the new "power" button before i could start entering the time, but i think i can live with that.

The other thing i realized is that i only need to use 9 buttons. For power 10 i can just enter the time. So i might get away with using just 3 i/o pins on the uC for scanning, one more for the drive, for a total requirement of only 4 i/o pins! Nice.

What i will probably do is set it up manually at first, where the actuator is operated with a small switch. I'll see how fast i can get it to go in and out because this is one of the screw type actuators not a solenoid. Unfortunately i have no way of knowing this until i test it, so if it is too slow im beat except i'll use it for something else. Got a couple of DPDT switches too for the initial tests (which allows reversal of the battery or source polarity without any extra electronics). I think this is going to be quite a lot of fun seeing it work :)
Eventually the pure electronic method will sure be nice. The only extra thing on the outside of the oven will be a long narrow keypad with 9 medium size buttons.
 
Hi MrRB,

Yes i'll have to post some photos too just for kicks.
A couple more days and the parts should be here.

BTW i found some real nice actuators on a Robotic sales site. Kind of pricey though at 50 dollars USD each. I think they handle up to about 150 pounds force however with decent travel time.
 
Since you said you are putting the solenoids on the side of the MWO and using a linkage, I don't think force is going to be a problem anymore. Solenoids generally have a travel of 6-10mm with max force at the final position, and the tact switches need quite a bit of force and surface area to reliably activate them BUT only need to be depressed about 2mm. That gives you an easy 4:1 or 5:1 leverage you can design in to your Frankenoven actuator linkages.

I bet a video of this thing when you get it built would go viral on Youtube... "Lazy engineer makes microwave press its own buttons" ;)
 
Since you said you are putting the solenoids on the side of the MWO and using a linkage, I don't think force is going to be a problem anymore. Solenoids generally have a travel of 6-10mm with max force at the final position, and the tact switches need quite a bit of force and surface area to reliably activate them BUT only need to be depressed about 2mm. That gives you an easy 4:1 or 5:1 leverage you can design in to your Frankenoven actuator linkages.

I bet a video of this thing when you get it built would go viral on Youtube... "Lazy engineer makes microwave press its own buttons" ;)


Haaaa haaaaaaa,

Geeze, that is funny. Let me guess, you moonlight as a stand up comedian right? :)
I really love comedy, almost as much as electronics.

And you're right it probably would be cool on You Tube, maybe i should do that. We all need a good laugh now and then, mostly now.
"Frankenoven" is also a good idea, very fitting.

I like that "press it's own buttons" part a lot, as that makes it sound like the microwave is somehow being punished for being so silly designed. It's a little something i like to call "Microwave button entanglement" :)
It sure would be nice if the original engineers would take note and modify the dang control program.

So thanks for that uplifting reply. BTW the actuator is a true actuator not a solenoid, but i guess that could be a good choice too at some point if i never go electrical. And as far as the pressure point, it will be shaped exactly like a human finger tip coated with a thin but not too thin layer of silicone and the main mount will be spring loaded to absorb the micro shock forces and the excess forces that could be generated before the true mechanical end of travel limit. So in other words, the pressure force profile will be matched to that of the human finger actually pressing the button with moderate force. Similar to but not exactly like pressing the button with a pencil with a squishy pencil eraser on the end.
 
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Hello again,


The actuator arrived today. It's a bit bigger and stronger than required for the pushing of a button. This thing would push the whole microwave right through the wall :) Seriously though i have to think about this again. Smaller voltage equals smaller force, but the thing is much bigger than required so i might try a different one. Maybe a solenoid would be better as i can get a much smaller one than this.
Now on to rethink, rethink, rethink. etc.
 
Hi MrRB,


I'll have to check that out. I found one for less than 3 dollars but shipping brings it up higher.
 
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