TinkerTech 1: Smart-Oven

I'm a bachelor. I live in an apartment. With my cat (who never helps me cook). And I'm okay with that.

What I'm not okay with is having such an old oven that I can't set it to bake a Costco meal to be ready when I get home! If you aren't there, you aren't baking. I suppose I am a tad spoiled after renting from my manager before he and his family arrived in Reno. Now that oven was nice.

So I'm contemplating an outfit to my apartment oven to provide room for programmability.

Big Picture

Present-day ovens generally have the capability to program an oven to pre-heat for when you get home or even to program the entire cooking session so the food is done as soon as the day's work. As a bachelor, such functionality on its own is sufficient cause for me to outfit this old oven with a programmable interface.

However, imagine texting your oven because you decided to pick up a Papa Murphy's pizza on the way home, or because you put the food in the oven, but forgot to program it before you left for work? This is my ultimate goal. I'd like to be able to text my oven with some of the following commands:

1. bake 425F at 5pm for 1hr 30m
2. preheat 100C 1700
3. bake 350 for 2hrs end 6pm
4. preheat 60C now
5. status

... with the result being:

1. The oven preheats to 425 fahrenheit starting at 10 minutes til 5pm, and turns off automatically 6.30pm
2. The oven begins to preheat to 100 celsius (internally converted to fahrenheit) 10 minutes prior to 5pm (1700 military time), but shuts off after 10-20 minutes to prevent burning down my apartment if I get stuck in traffic
3. The oven starts preheating to 350 fahrenheit at 3:50pm, so that it can cook from 4pm to 6pm, when I plan on being home from work
4. The oven preheats to 60 celsius starting immediately, but safely shuts down as previously indicated in scenario #2
5. The oven responds with what time it thinks it is, what are its current settings if it is running, when is the next programmed cooking session, etc.

This is a long-term goal, of course. I will likely have an LCD display to start so I can program it before I leave the house. And to do that, I first must find a way to interface with the existing oven. There are two potential approaches. One is mechanical, one is electrical.

Mechanical Approach

The mechanical approach is quite simply to interface two servos, one to each of the knobs below.

Figure 1: The knobs on my old-fashioned, non-programmable
apartment oven

With the knob covers removed, its clear that I have easy access to two different shafts (Figure 2).

Figure 2: The knobs to my oven, but with the k nobs removed.

For this mechanical approach to work, I will need a plate to which to connect the servos. If I have the plate Laser-cut out of some sort of acrylic or polycarbonate, I'll probably use a shape similar to that in Figure 3, but if I have to make it myself out of metal, I'll use the shape in Figure 4 to prevent covering over the knob annotations.

Figure 3: Plate design for translucent material.

Figure 4: Plate design for opaque material.

The benefit of a mechanical approach is that I won't have to take anything apart, aside from removing the plastic knobs. Furthermore, the plate spans two knobs which means that the plate is locked in place and can provide the servos with a steady base from which to reference their position.

Electrical Approach

I have yet to confirm this, but if these two knobs are just large potentiometers (as suggested by my electrical engineering coworker, Nick), then there may be a purely electrical solution involving digital potentiometers attached in parallel to the existing potentiometers.

The benefit, if this approach is feasible, would be that the oven can be used manually or programmatically, and the setup will consume considerably less power than one running servos. The downside is I'll have to take off the oven faceplate to run some soldered-on wires from both of the existing potentiometers.

Conclusion

I would clearly prefer the electrical solution if feasible. I'll just have to take off the faceplate to see how these oven knobs currently function. I have a feeling, however, that the mechanical solution is going to win this time.

If you have ideas or suggestions, please feel free to comment. Otherwise, keep an eye out for the next TinkerTech Thoughts article.