Introduction: The Microwave Digital Timmer Hack.

I am rather the absent minded sort of guy. To put it another way my memory stinks so if I get distracted from a project where I might have a hot soldering iron smoldering away, I could completely forget it and later burn myself. This has been a big problem until I had this thought. Microwaves have to handle a lot of power. To do that they need some pretty beefy switches. In other words they are digitally controlled relays. In this Instructable we explore the possibility of repurposing one.

If your not completely comfortable with working around electricity, DO NOT make one of these. Under no circumstances should you operate one of these without building a case of some sort. I would recommend a metal project box. That way you can ground it which makes the thing a whole lot safer to use. Without a metal enclosure of some sort you could get a nasty shock. Trust me those aren't fun at all. Avoid those at all costs. Below is a picture of the one I use to control my coffee pot. As you can see it's encased in an old aluminum project box I had. I know it's not pretty but then the best things in life often aren't.

In a side note: be sure to read through the whole project before you start working. You can always go back later for reference.

Step 1: Parts for This Project...

The first one is obvious. You need an old microwave. Preferably one that's being thrown out because it's stopped cooking like it should. One from a yard sale or the local thrift store will work. Why use a second hand device you ask? Well first of all it will be much less expensive. Second, it keeps part of it out of a land fill. Lot's of people don't recycle those and it's a crying shame. There are a lot of useful parts in them. All kind of things like microswitches, screws and other hardware, and let's not forget the emitter it's self. Then there's that huge step-up transformer. There's a chance that the emitter or the transformer are damaged in most cases. The switching device is usually still workable. That's just what it is too. A programmable switch.

The tools you'll need are as follows:

1. A Soldering iron and solder
2. Wire cutter/stripper
3. Various screw drivers (depending on what they put it together with. It varies between makes and models.
4. A Dremel or some other means of cutting metal and plastic.
5. A drill or you could just use a drill bit in the Dremel
6. Safety glasses (You won't be able to do this if you can't see because something got in your eye. It happens, just trust me and use a pair.)
7. A multimeter (preferably digital because their more accurate.)
8. A power cord (the heavier, the better.)
9. Some outlets and boxes (I used panel mount outlets that I got from Home Depot)
10. A hot glue gun (This is optional depending on how you plan to build it)
11. Electrical tape

Step 2: OK, Lets Get Started...

Let's get this thing open. Look it over first to see where all the screws are. Make sure you get all of them undone. After you get the screws out the case should come off pretty easy. If it doesn't you missed one somewhere. The first rule is "Don't force it" and I stick to that pretty sternly. Sometimes you don't have to be careful because you don't have to care what it looks like when your done. The main reason I don't force it is safety. Think about it. Your prying apart thin metal that can cut you fairly easily. Work smarter, not harder.

Once we get it open it's time to tear out the guts. It's a simple process of removing more screws and maybe some nuts and bolts. Here it's a good idea to pay close attention to how things were connected. That will help a lot in the next step.

Next let's separate the timer from the rest of the machine and get rid of unwanted pieces of hardware. In the one I used there was a large loop surrounding the microwave's door frame. I had to cut that away because I didn't want it to be that huge when I was done. Situations with this will vary from model and make. I decided to use the piece that the keypad was mounted in. You can make a custom mount for it if you want to. I find it's easier to use the vacuum formed piece that the factory built for us. It's not as pretty as it could be. It does save a load of time with assembly and it's way easier than making your own.

Step 3: Now That We Have It Apart...

First we have to figure out the electrical pathways that we'll need to use. The first one we'll need to locate is connected to larger of the two relays your likely to find. That's the one that turns the stepping transformer on and cooks the food. Trace back from the point where the stepping transformer was connected to be sure you have the right one.

The other one is for the internal light that lets you see the food as it's cooking. This is important only if your planning on using it for high wattage devices. You'll want a cord for it that will handle what your using it for. What I've found to work best for this is the cord that was on the device to begin with. It's rated for about the maximum that the device should handle. We can also save the cord strain relief for use in our project.

Step 4: Getting Ready...

I would suggest using more than one outlet. Most of you should know not to plug lots of things into it. That said let's be logical. You should have a set of outlets for the main and one connected to the relay for the light. If you want to, you can put a switch in line with them as well as a master kill switch. These are for when things go horribly wrong and they can. I speak from experience in the matter so take my word for it. It doesn't take much to short things out and you'll want a way to shut it off without touching anything dangerous. It's a safety precaution so take it or leave it.

The reason we have the outlet boxes is for the secure mounting of the outlets. If you decide to use panel mounts like I did you'll probably want to hot glue them from behind. This is just to make sure they don't pull out when you go to unplug things from them. It's just some added insurance.You'll see that I used a bridge buss to connect everything in this one. I got that out of an old CB home station that was discarded. I'm not using this for heating or anything heavy duty so this is substantial enough for my needs. You may want to use a screw terminal or just solder wires directly to the PCB. I did it this way to save wear and tare on the board if I should want to reconfigure it later.

Step 5: Now We're Ready to Start Building.

First things first. Decide what your going to build it out of. If your going to use wood be sure to paint the inside to help seal it from getting moisture build up. Again, This is a safety precaution, Though it's not likely that it will get wet, I take this step just to be sure it doesn't become dangerous. At least not as bad as it could get without doing this. I don't know if you've ever touched a hot wire while in contact with wet wood or not. I have. Luckily it was just an electric fence. It hurt pretty bad but luckily it wasn't harmful. It sure felt worse than it was. That is to say that water and electricity don't mix well whereas human contact is concerned.

That said PLEASE, DO NOT use this around water or liquids of any kind. That means you don't use it for the bathroom heater GFCI (Ground Fault Circuit Interrupter) outlet or not. It's not safe to use this around sinks or bathtubs so don't do it. If you use this in a wet environment and get hurt, remember I warned you about that. So people PLEASE be careful.

Now that the safety stuff is out of the way let's get on with it shall we? Regardless as to what your using for your materials, your going to have to make holes in it for the outlets. We can do this one of several ways. The first way which is what I did, is to use our Dremel and a cut-off wheel. It makes pretty quick work of metal or the type of board that I used for the front panel. They also work pretty well on plastics. The only concern there is that the plastic tends to melt with the friction which can send chunks flying towards your eyes and face. This would be a really good time to don those safety glasses. Trips to the hospital should be social visits, not necessary emergencies.

What ever material you use make sure you don't over work your Dremel. You want to put just enough pressure to keep it cutting but not enough that you might break the disk. If you do break one chock it up to a learning experience and be glad it scratched the safety glasses instead of your eye. You could also use a router for this. Another good set of tools would be a drill and a jigsaw. If you use standard household outlets you could even use a hole saw. Whatever your method be sure to mark and cut very carefully. Remember, you can always take more material off. If you cut to much it's gonna look sloppy. That's not to mention that things won't fit quite right. This is why I suggested standard outlets. They can be mounted in wall boxes which makes them a lot safer than most other types of power outlet.

As a matter of fact you could use the inlet from an old computer power supply to give your project power. It would make it more portable because the cord could then come off. I have no idea why it would need to be that portable as I've never had to take mine anywhere or had a reason to. It's just a thought I had one day while I was moving into a new house and tripping on the cord. See? Safety. Not the best idea if you plan to use it to limit the on-time of a heater or large halogen sun lamp (good timer for a home made tanning station.) Just be careful not to overload the cord or relays. Why yes, this is the reason for the master kill switch. Thank you for asking.

Step 6: OK, Now Let's Get Connecting...

For those of you who don't know. Yes I understand that there are a lot of people who do, but for those who don't. The following was written for you. Let's learn a little about electrical wiring shall we? The cord you should be using will have 3 wires. If their color coded the white one is the neutral. That's the one we connect directly to the outlets and the board. It's best to use some sort of buss connector like a screw terminal strip with bridge clips. If that's a little too much for you just put a white wire on one of the silver screws of each outlet and one to the contact of the board that had the white wire on it. Then take the other end of them and use a wire nut to connect them together. You could also solder them and put electrical tape over the connection but that isn't near as safe. The tape could degrade and leave the exposed wire to short out against the components on the inside of your project. That is a fire and shock hazard.

The green wire or in some cords, the one in the middle, is the ground. This is the path for major spikes of electricity to jump towards in the event of a lightning strike. It's better the ground wire takes the jolt than you. If you used a metal case I want to congratulate you. That is the safest enclosure for this project. In a metal case you can drill a hole in the side and use one of the machine screws and a nut salvaged from the microwave to attach a ground to the case. For that you can take the piece of wire that was attached in the microwave's ground and reuse it here. For those of you using wood as your enclosure type you'll need to attach a piece of wire to the green screws on your outlets and wire nut them together with the ground of the cord. This isn't necessary with a metal enclosure because the frame of the outlet where the wire would normally be attached is touching the metal of the case. Therefor if you ground the case the outlets are grounded too.

The last wire is the hot wire. This is the one that goes to the board and from the output of the board (after the relay) to each of the outlets' brass screw. This connects them with the proper polarity so we won't get shocked if we touch the outside of a lamp socket. That's why most lamp cords have polarized plugs on them. The fat side of the plug is the neutral. That way if you go to turn on the lamp in the dark barefoot on a concrete floor, you don't get a nasty surprise. This is why I get after people for filing or cutting those off. They do it so they can plug them into regular nonpolarized outlets. That is a phenomenally bad idea. Remember the cement floor? That's a ground too. You can get a serious jolt if things aren't hooked up properly. That's why the world has electricians. So people who are clueless don't die.

We'll attach the cord in the next step so don't do that just yet.

Step 7: Time to Get It All Together...

OK, by now you should have all your pieces cut and ready to accept your hardware. If your timer has a plastic shroud on it still like mine does, mounting it is simple. Simply put it flush with the surface of the box and drill screw holes. If you do this with it in place you'll have a much better chance of everything lining up when you go to assemble it in a few minutes. This can be done with a drill or my favorite tool, the Dremel. For metal project boxes you may want to modify your cut a little. Leave tabs you can drill holes in and bend down to meet the sides of the plastic. That way you have a perfect mount point. The one shown in the pictures for this project was the prototype for the rest I've built. It still employs the same principals. In other words, it was what I had when I built it.

With everything attached to the cover, let's take a minute to make sure our connections are all correct. I shouldn't have to tell you what will happen if we get it all put together only to find that it sorts out or doesn't work at all. It's better to catch any problems now while it's still somewhat apart. That way we can fix them and avoid having to tear into it later.

Once your sure that it's all correct we're ready to put the cord into the box. The reason we held off till now is simple. We can drill a much smaller hole because we don't have to fit anything but the cord it's self through it. OK, remember that cord strain relief we salvaged from the microwave? That's how big the hole has to be. If all you have is your trusty Dremel you can drill a few small holes and remove the extra material with a grinding wheel. Dremel makes several sizes, shapes, and compounds. I chose the green aluminum oxide stones because they last the longest and work on glass too.

For those of you lucky enough to get a screwed on strain relief like the one on the back of this nuker. Instillation becomes much easier. Just use the hole it left in the microwave case as a template to cut your own in your box. These are the best for wooden boxes as they don't require a compressed fit.

Now let's attach the lid to the box and see if it works. You should place the lid on top and drill pilot holes with it in place like we did for the control panel. In this situation I would suggest taking the lid off and drilling the holes a little bigger so the screws don't bind in them. that is unless you bought a project box for this at which point it already has screws and pre-fitted holes already in place.

This one already had a hole that was unfortunately to big so I made the best of it and taped the strain relief onto the cord. Notice I screwed in a tie down to keep the cord from pulling out. It is agreeably by far not the best way to do it. Just remember this is my prototype. It's also the project I choose for my first Instructable because it is by far one of the most useful things I've built so far.

Step 8: Let's Get Cooking...

Pardon the pun, I couldn't resist. All you have to do now is plug something in and set cook time. Then press start and watch what you plugged in turn on and then off when the time has elapsed. I would suggest something visible like a fan or a lamp. It will be much easier to tell if it's working if you can see an immediate result.

If it has "delayed cook" or some similar feature you can use it as an alarm clock that can turn on lamps or even a stereo. It can be used to limit the amount of time your kids get to watch TV or play their favorite video game. You could use it to turn lights on when your about to get home.It could be used to time and electric blanket to warm your bed before you get into it and not have the fire risk of just leaving it on all nite.

It could be used as a sleep timer if you fall asleep relatively fast and providing the beeping doesn't wake you back up. Of course you could always take the piezo element out so it won't do that. That would be the little round thing with the hole in the middle. Their usually black and about a half an inch in diameter. You can either heat the solder and pull it out or use the Dremel to cut a channel through the trace leading up to it. If you cut the trace you could solder in a switch to turn it on and off at will.

You can buy cheep coffee pots and make them into a programmable one. You could even control the temperature of the coffee if you set it to one of the lower power settings. Ever notice the buzzing noise that happens periodically when you have something defrosting in there? It doesn't regulate the amount of power to the emitter. It just turns it on and off. That being the case it can easily regulate the power to your coffee pot in the same way.

Any way you choose to use it, I can assure you that it will delight you. It is after all something you built that's pretty, well....useful. Just be sure to be careful. Use common sense when deciding when and where to use this project. Last but not least, enjoy...

Comments

author
teachandlearn (author)2013-08-14

One nagging question is, a countdown shutoff timer is so useful, why isn't it available as a finished product?

author
Treknology (author)2010-04-04

This is one of those "Why didn't I think of that?" things.

My coffee maker heats and runs water into the filter too fast and if not watched up to 50% of the water can just run down the over-flow into the pot having never seen any coffee.

A microwave control panel is the ideal solution. Put it on low/medium and set it for 1/2 hour and it should take four or five "sessions" to move all the water through allowing enough drip time and ensuring that I have my high-caffeine product!

author
frikkie (author)2009-05-11

Its a bit big but it a very nice project.

author
killerjackalope (author)2009-01-02

This is a pretty nifty project, the only thing it could do with is some more pictures, though it's a clever use of an old microwave...

author

I wouldn't worry about things like that, Instructables is more interested in having 1st rate postings that attract viewers than bandwidth or HDD space. Besides, they've probably got more than enough to cover everything that anyone could possibly post and these days picture files are not all that big.

author
Koil_1 (author)killerjackalope2009-01-05

I know. I kept the number of pictures low to reduce bandwidth usage and save storage space for others. This means that Instructables.com doesn't have to spend as much on info structure and bandwidth for their servers. Simply, I'm just trying to be considerate.

author
killerjackalope (author)Koil_12009-01-05

Odd reasoning, they do have space to spare and like their pictures... During a Q&A; it turned out 'ibles took up a couple of terabytes in its entirety...

author
okieinAZ (author)2009-01-03

This is EXACTLY why i have been scouring second-hand stores lately for old microwaves. As soon as I see on e for under $10, I will buy it. Even if it has the non-digital dial timer. I need to control my soldering iron's tendency to leave itself on... Thanks for your instructable.

author
Spokehedz (author)okieinAZ2009-01-04

First: Excellent 'ible! I am going to have to start looking out for old micros when I drive around now. I bet I will never find one now though... >_<

But in reply to Okie...

I really must advocate buying a temperature-controlled soldering station. It simply cannot be bought or created at home. For many, many reasons, but the best one is that this one has a 99-minute timer that will turn itself off when it hasen't been in use. How does it know? It monitors the temperature, and if it sees that the temp remains the same (and dosen't have to boost the heat signifigantly, like soldering would cause) then it shuts off.

http://www.action-electronics.com/wewes51.htm

That is NOT the cheapest, but that is the first result on google. HOWEVER, it is worth that price, but you can get them for $75 if you look hard enough. Oh, don't think that it is worth that much for something that just gets hot and melts some metal? Trust me. I spent years, and years working with very bad irons--and making mediocre joints, which would eventually fail, trying every technique that every book on soldering had to offer... only to find out that had I bought a good tool in the beginning I would have saved myself countless headaches.

Don't buy cheap tools. False Economy. Yadda yadda yadda...

author
Koil_1 (author)Spokehedz2009-01-05

In response to your addage about temperature control. It's easy enough to just ad a simple dimmer switch to the box your working on. As a matter of fact the one I have for my soldering station has one in it. If you get the nice triac controlled ones they work really well. If you think about it, the heating element in a soldering iron doesn't draw any more than a low wattage bulb (usually under 45 Watts) and this makes it really easy for us makers. A dimmer will easily control that much. You can add a small night lite bulb if you want to gauge the power level. Another way you can vary the temp of an iron is to put in an in-line rectifier diode with an override switch to bypass it. That effectively cuts the heat cycle in half giving you about 2/3 the heat. My opinion is, why buy it if I can build it well enough...

author
Spokehedz (author)Koil_12009-01-05

You certainly can try all those methods. I did, and they were just very unreliable. At least compared with my soldering station I have now. What did I try? Lots of things... 'Simple' Dimmer switches. (buzz, got hot, never was able to get fine enough temperature control) Variac (Big box, finicky temp adjustment, it sat on the floor while my iron was on the bench.) Adjustable DC Voltage & Amperage (worked okay, but changing irons or tips would radically change the temperature.) DC PWM Voltage/Amp (Again, worked but each iron had it's own settings and each tip for each iron...) Various methods of working quickly and moving fast--which only resulted in me making bad joints or getting burned. You get the point. Oh, and what I never mentioned on any of those was the time it took for the irons to get to temperature--well over 10min. My weller? less than 20 SECONDS. Not only that, I never knew what temp my iron was actually at until I bought a thermocouple for my DMM--and even that was wildly in accurate at times. Trust me when I say that setting your iron to the lowest temp possible for what type of joint you are working is a wonderful thing. No more boiling off the flux before you get a good flow into the joint. No more using a big 50w iron with a big tip for power bus wires or mechanical strain relief. Then having to switch to the little 30w for the other connectors on board, and then down to the 15w for the surface mount stuff--each switch taking 10-15 min to get to temp. So, again, if you get by with your iron the way that it is--by all means, don't change a thing. If you are happy, then that is ultimately what matters the most. It doesn't matter if the tool is the best in the world, you will use what you are comfortable with. I was just trying to inform about some of the benefits of getting the soldering station. That's all.

author
killerjackalope (author)Koil_12009-01-05

If you really wanted to get fancy a simple adjustable thermostat wouldn't be difficult to add you could add one from a lot of things really...

author
Koil_1 (author)okieinAZ2009-01-05

Your very welcome. Though often times if you watch, you can find someone throwing one away. Check the slums of your town and look for junk trailers. Also ask the managers of your local apartment complexes. They will often times have discarded appliances that you can have for very little money if not free. Finally, if you do find one in a junk pile or a dumpster. Ask the respective parties if it's OK to take it. I don't know why people get so upset when you take something they were getting rid of but they sometimes do. Better safe than sorry...

author
Phil B (author)2009-01-02

Old microwaves seem to be a favorite source of parts for people at Instructables. You guys are making me think of all sorts of things in new ways. Maybe I am unusual, but it seems any microwaves that bit the dust in our family were recycled by the folks who sold us the new one. I have also seen hand-me-down microwaves that got a new life because a new owner found and replaced a blown fuse, etc.

author
Koil_1 (author)Phil B2009-01-05

Agreed. They do have a lot of uses that most people would overlook. One thing to be mindful of is that some appliance stores simply discard the old one into their dumpster. They only say their recycling it as a sale incentive. The point of advice here is to sneak around behind their building and have a look at what evidence you can find either way. Obviously if they are just throwing them away instead of recycling when they claim otherwise, they aren't going to be honest if you simply confront them about it. You can also just ask them where they recycle them and check with that company.

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Bio: I like voiding warranties. There isn't much I own that I haven't modded in some way. I love science and music as well ... More »
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