Perfect Toast Every Time!

[Beeper]

Me and my girlfriend have very different ideas on how to toast bread. She likes it light, I like it browned. She has a toaster that stopped working, it was just a cold solder joint on the browning adjustment pot that is turned by a knob on the side of the toaster, so I fixed it, it works ok again, but why should I settle for just OK?

I want to upgrade the 555-timer circuit used in the toaster now with a state of the art micro-controller.

The toaster always works well when first used and cold, but after heating up, I must always remember to retard the brownness adjustment knob (it adjusts a pot on the internal circuit board) to keep the toasting from too-toasting after the first set of slices.

The toaster does have a thermistor hanging off the 555 control board for toaster cabinet heating compensation with many-slice toasting, but this simple 555 circuit just doesn't quite give me the results I want.
 
I am experienced with PIC and C-language and Arduino microntrollers and know how to make electronic circuits work, know how to get a MCU A2D working with a thermistor. And i already have the circuit board size, with the pot position's layout and it's power supply circuit can be easily made to regulate 5V for the MCU. This makes it somewhat easy to convert this toaster to micro-controller operation. And I know how to make breadboard a circuit, make the PCB, power the MCU, sense the temperature, program a MCU for function as a timer.

I just have to get it my MCU to set timing correctly each time, sot that it compensates for toasting heating effects by getting a reading form the thermistor for feedback.

Has anyone made  some programming strategy to work with the common toaster, to artfully get a MCU to activate the magic solonoid that makes the bread jump out at the perfect time?

Is trail and error, toast and burn, the only way I am left to to somehow perfect the perfect toaster?

I realize the following variables:

Bread Moisture Content
Smoothness of Bread Surface
Bread inserted's initial Temperature/Thickness/Density
Whether there are 1 or two slices to toast.
Multi-Toast Toasting Time Effects because of internal cabinet heat-up after the first toasting.

Maybe it would require me  to guess how to preset the browness knob just once to help the MCU to get it right.

[tom66]

I am reminded of this.....
http://kcbx.net/~tellswor/bettoast.htm

[jc101]

I have a see through toaster, so it's always just right every time...

http://www.magimix.uk.com/products/BREAKFAST/Toaster/Vision-Toaster/

[Excavatoree]

More powah!!!!!!!!!!

[Beeper]

One toasting effect I have just noticed:  Although the toast seems to slowly rise to a browning temperature, once browning begins, the browning effect very quickly progresses from tan to brown to black. Time is of the essence, else essence is smoke.

I think this is what your diagram shows, 3roomlab, but the slope from tan to black is quite steeper.

I think this is what is going on:  The bread heats slowly and probably linearly  until  bread surface moisture is evaporated. During this time the bread exposed surfaces have a low thermal resistance and bread surface heat is quickly conducted to the core of the slice, cooling the toast surface and the toaster by conduction and moisture evaporation. Also moisture is likely diffusing at first to the surface area and this sustains a slow temperature rise of the the surface toasting area.

Once surface moisture has been exhausted, heat transfer to the bread surface is very rapid as the thermal resistance of the bread's surface becomes very high and browning proceeds very rapidly.

[Beeper]

All I know is that you can buy croutons and they are all perfectly toasted and I couldn't make the payments on my Maserati if I bought one of these elegant toasters shown by other posters.

[IanB]

I would try to design an optical technique. Have a light sensor aimed at the toast and use it to measure the change in light reflection as the toast browns.

[Beeper]

IanB:  A great idea, I wonder how to implement these optical components? How would you mount them, get them to fit into a stainless-steel-two-slicer, top-loading, push-the-lever-down-to-toast-after-setting-browness-knob 555 animated toaster?

[m100]

You want perfect toast?  Just how stable is your mains supply voltage?  Is your bread always fresh and baked exactly the same every day?  Do you use stale bread to make toast, if so how many days since you bought the bread?  What temperature is it kept at?  What is the room temperature? What about the relative humidity? What happens post pop up if you don't remove the toast immediately, does the residual heat affect the finished product?

Lots of variables, could be an interesting project but personally I'd either either watch it, delgate it or if I ever win the lottery employ someone to do it for me.

[Beeper]

M100, this is an expermenter-hobby-DYI board. The spirit should be to attempt the possible, even attempt the likely impossible, not hire someone else to have all the fun! I think this board is a place to learn about electronics, programming, etc.

Not every multi-million $$$ space rocket makes it far off the earth, as the news has recently shown, but one must enjoy trying.


If it can work fairly well with a 555 circuit, why not try for MCU?

BTW, we usually buy the same type of bread, I do have a favorite, and sometimes we keep the loaf inside the oven(without heat, of course) as a bread storage area, sometimes we shove the opened loaf into the fridge. So the raw materials are consistent, the room temperature gets cooler in winter, but the toaster doesn't seem to care that much.

[lapm]

If i would be doing this i would at first limit variables in just couple you can control: Time, starting temperature and goal temperature.

From these you can do things such as heat profiles, etc...

Of course you need ability to reliable measure brownes of end result so you have feedback to all these functions...

Maybe integrate heat exposure over time to slice of bread? and observe effect is has for color of end result?

[miguelvp]

PID controller like the many reflow oven controllers available everywhere will do the trick.

Record your profile for what is your perfect toast per user. Then you can select what user and type of bread or whatever other variants you need and make sure the controller keeps follows the profile.

and on the plus side you can use it on a separate and dedicated toaster oven for reflowing your boards, maybe get a separate thermometer for each so you don't get lead contamination on your toast.

[jucole]

We have a Dualit toaster, so I just take a guess based on the type of bread etc and then just spin the mechanical timer dial - easy!

[denelec]

I would try to design an optical technique. Have a light sensor aimed at the toast and use it to measure the change in light reflection as the toast browns.

I also think it's a good idea. 
The problem will be to protect the sensor from the heat.

I remember, when I was a kid, our toaster always burned the first toast...

[Someone]

One toasting effect I have just noticed:  Although the toast seems to slowly rise to a browning temperature, once browning begins, the browning effect very quickly progresses from tan to brown to black. Time is of the essence, else essence is smoke.

As you go on to note, its that the temperature will runaway when you are using the traditional radiative heating approach.

All I know is that you can buy croutons and they are all perfectly toasted and I couldn't make the payments on my Maserati if I bought one of these elegant toasters shown by other posters.

Temperature is the key, if you toast with a contact method (sandwich press) and set the temperature accurately you can chose a level of brown and leave the bread in there almost indefinitely without burning. The crouton factory is probably using a large continuous process with a well controlled and uniform temperature forced air oven.

[hamdi.tn]

nice project  will be fun to test if it work correctly every morning  i think that the heating energy is what you should take attention to, i think for the first bread when toaster is cold , the heating energy is slowly exchanged due to the fact that both toaster and bread are room temperature and there temperature increase with " equal " rate, so the total heating energy is equal to an integral of temperature difference multiply by some factor over the total heating time. Things will no be the same for the second bread that will receive much more heating energy if exposed to that maximum heat for the same time.  long story short , measure the room temperature for the first run before start heating, then calculate the needed time to transfer the same heating energy as the first time. The first heating time will be determined by the knob. Try to put that heat transfer into some imperial  formula and you will get some precise result.

Some useful data :

Q = M Cp ?T
where Q is energy
M bread weight
Cp thermal capacity , for the bread it's 2.93Kj/(Kg . °C) (someone actually measured it  )
?T  temperature difference between toaster temperature and bread (room) temperature.

and
P = Q/t
where P power used , t heating time

I think what you need to do is make sure that power is the same overtime for all your bread

[Beeper]

I realize in attempting this toaster improvement project that practical limitations such as safety, cost and time must limit the end result.  My MCU toaster may not always toast to perfection, but I am aiming to create a toaster that does better than the 555 solution.

        May God, grant me the serenity to accept the burnt bread I cannot toast,
        The courage to try to find the way to better toast the bread I can,
        And the MCU wisdom to know the difference.


        Toaster's Anonymous Prayer

[moffy]

I think you will need to use a feedback mechanism, like optical, because the variables are very variable. For raisin toast you have to shorten the time, for english muffins they need a long time with white bread somewhere in between. Maybe if you used a smoke detector with a variable threshold you could control the browning effect.

[Macbeth]

I believe you are missing the most important factor in making good toast - how to apply the butter in the perfect quantity and at what temperature to spread it. Nobody likes soggy toast.

Thankfully some very important research was done by Leeds University over 10 years ago.. I am sure your perfect toaster could indicate when to arm the butter knife, measure the butter temperature and weight on the blade, and indicate the right time to strike the pats of butter after the toast has been ejected at its perfect toasty browning.

The one thing I hate about perfect buttered toast is it has to be eaten at exactly the right time, once it cools it loses its magnificence as the ambrosia of the gods. Toast racks should be electronically heated and monitored. Also chucky eggs and soldiers - the soldiers are all cold by the time they get to the egg dipping stage. 

[Beeper]

Just some idea. I am still brainstorming my project before committing to its implementation.

Firstly, the 555-timer circuit does a pretty good job, I only want or probably need to get a MCU to do a better job.

The key to toasting success with the original 555 design was to become a sophisticated toast maker. After a few slices of my favorite bread, I could correctly re-position the browning control to compensate for a heated toaster or compensate for the few different types of bread and bread temperatures I would encounter.

I just want a MCU to somehow get close to getting toasting right without me having to fiddle around with some bureaucratic toaster user interface having some fancy LCD screen or many pots to set moisture content, mass, initial temperature, etc.

What I will finally make must be simple to use.

But maybe I can accept adding a few momentary-contact buttons to give the toaster MCU some insight into the specific toasting task? A button for thick bread, cold bread, for instance? And tiny LED's to indicate these toasting customizations have been turned on for the current toasting session?

I just have to find some safe, clever way to make my toaster work better, I don't need perfect and neither me or my girlfriend will tolerate a complicated setup or toaster operation.

I have salvaged some infrared motion detectors from an automatic light that detects the presence of moving humans in it's vicinity. I wonder if I can somehow embed a single glass fiber optic to be positioned close to the surface of the toast and safely couple infrared light within this very thin heat-resistant thread of glass to some sensor on the PCB and get an idea of the heat radiated from the surface of the toast toasting to give me an idea of the toast surface temperature? The problem is that with these types of  infrared detectors, they want to detect moving objects, while a toasting slice sits still during the hot ride it is on.

Would an infrared sensor(such as above) detect the rate of change of temperature at the critical start of toast temperature?

I also know that I can purchase an infrared hand-held temperature meter that can accurately see the heat of a remote object, and I can cheaply buy this instrument this week on sale at a local store. In this way I can measure the surface temperature of the perfectly toasted toast at the instant of its final ejection. 

I can easily control the heating elements with a TRIAC and PWM to preheat the toaster(and the bread) to some standard temperature, thereby normalizing the starting temperature. The main consideration here is that this operation must not take too long. I would accept about a minute or so of first slice use  "calibration" by the toaster.

At the same time, I do not want to dry out the bread during  this calibration.

I have a theory:  Once the surface of the bread reaches some critical temperature, the optimal brown to perfection toasting time can be accurately approximated by the MCU to correctly then apply the coup-de-gras heat dose.

[Beeper]

I think that Hamdi.fn is on to the right approach, I must just find the correct heat dosing and and a way to sense it.

I just wonder how much time it would take to develop method to get meaningful data about the thermal dynamics of the the toast and the toaster. I do not want spending too much time in R & D effort.

[Beeper]

I would not be as concerned as Macbeth as to buttering my toast.

I greatly enjoy upon wake up two slices of my favorite: toasted multi-grain bread upon which I apply peanut-butter and marmalade, but my girlfriend just wants a lightly toasted slice to go with her morning coffee.

[pickle9000]

Talkie Toaster 

[Macbeth]

I would not be as concerned as Macbeth as to buttering my toast.

I greatly enjoy upon wake up two slices of my favorite: toasted multi-grain bread upon which I apply peanut-butter and jelly.
My girlfriend just wants a lightly toasted slice with her morning coffee.

Oh no, I think we have one of our colonials here. PBJ? for breakfast? bleurgh!

[Alex Eisenhut]

I believe you are missing the most important factor in making good toast - how to apply the butter in the perfect quantity and at what temperature to spread it. Nobody likes soggy toast.

I freeze sliced bread, and keep butter in the fridge. When the time comes I slice off chunks of butter, put them on the frozen bread and put it all in a toaster over, flat of course.

When you get it just right, the butter sizzles and juuuuust starts to brown itself as it soaks into the hot bread.