Solrmatic with an oven on top dehydrating apples
Solrmatic with an oven on top dehydrating apples

MF14BA_Badge-01In a nutshell, the Solrmatic is a Raspberry Pi-powered rotation device for a solar cooker allowing the solar oven to get hotter or cooler based on the program you input. You can put an off-the-shelf solar cooker on top, or even build your own. We’re excited to show off Solrmatic at Maker Faire Bay Area 2014, so please stop by and say hello!

The problem with traditional solar cooking is that the sun’s solar radiation varies with the seasons and daily weather. You also have to rotate it manually, leaving a lot of guesswork. You are either stuck cooking recipes such as stew or beans, and you must be very attentive to your cooking and monitor temperature very carefully. Also, the sun only shines in the daytime, yet people eat dinner in the evening. If you arrive home in the evening to start cooking, solar cooking is out of the question.

The Solrmatic solves these problems because it features thermostats, time delay, timed cooking, and web monitoring, allowing you to cook almost everything you cook in a traditional oven. The Solrmatic has cooked leg of lamb, brisket, veggies, bread, cookies, and even bacon. We’ve also dehydrated apples.

Operation

Solrmatic faceplate with LCD and controls
Solrmatic faceplate with LCD and controls

The Solrmatic has four knobs, one switch, and two temperature probes.

Switch: In Set/Idle mode, allows for settings to be adjusted; or in Run mode, allows for the Solrmatic to work its magic.
Knobs for adjusting settings:

  1. Oven temperature: just like your oven temperature knob on your conventional oven
  2. Food temperature: If you want to stop cooking at a certain temp, this will cancel all further cooking and turn the cooker away (perpendicular) from the sun. This is important for recipes that you want to cook only to a specific temperature, like roasts.
  3. End Time: When you want your meal to be done
  4. Duration: How long you estimate the meal will take to cook. The duration will cancel cooking regardless of whether the food temp is reached.

Temperature Probes: There’s one for the food and one in the oven.
The set temperature and current temperature are displayed on the LCD. The current oven and food temperature are sent to the web via wi-fi for viewing so that you can make sure things are going well while you are away.

There are a lot of systems working together, all managed by a Raspberry Pi. This is how temperature, position, and other inputs are read to control the orientation of the solar oven. The outputs are the LCD and the stepper motor, which enables the Solrmatic to precisely rotate.

Raspberry Pi (left). Stepper motor driver and real time clock (middle). Analog to digital controller and voltage divider for temperature probes (right).
Raspberry Pi (left). Stepper motor driver and real time clock (middle). Analog to digital controller and voltage divider for temperature probes (right).
Behind the controls. Regular 10K pots for input. LCD display for output.
Behind the controls. Regular 10K pots for input. LCD display for output.
Stepper motor and rotation mechanism. It is hanging upside down since originally I build it the other way around. I changed my mind, so now the whole device rotates instead of just a platform.
Stepper motor and rotation mechanism. It is hanging upside down since originally I built it the other way around. I changed my mind, so now the whole device rotates instead of just a platform.

If you’d like to take a closer look at Solrmatic, please come see us at Maker Faire Bay Area 2014! And if you’d like to build your own, keep an eye out for an in-depth how-to soon. You can also follow our progress at the Solrmatic Blog.

9 thoughts on “Cooking with Raspberry Pi: Solrmatic Programmable Solar Cooker

  1. Very cool project, well done. Aren’t you worried about wires popping out of the breadboard? Do you plan on making the wiring more robust at some point?

    1. Yes wire popping out is a constant worry. It has happened a few times and I wonder at what point I will forget where the all return to. As soon as the design is finalized I’ll make a more permanent version. In fact I’m on Gen II which has reduced my breadboards from 3 to 1. Still some problems with slip rings, absolute position sensors, compasses etc I’ll post my progress on Gen II within a week or so on the blog.

    1. Yes, a perf board or simply sending out a design to be fabricated would be the next step. I’m still testing though. Auto sun tracking definitely opens up what you can do with solar cooking. If you take a look at blog.solrmatic.com you can see what we have cooked. We even cooked mmm….Bacon.

    1. Hi Jay, looked at your cool project and yes you could very well use the same sort of logic for a solar cooker. I don’t know what you did, but I see a GPS and a compass. With UTC time, azimuth and altitude is a snap. This is what I did, but I don’t need a GPS since the location does not change. Saves $30. also, I only need azimuth since tilting my particular solar cooker would spill the food.

      1. Very cool stuff, Mike! I am always fascinated by the different project approaches to solar tracking. Thanks for sharing!

  2. Hi Mike,

    How did you decide how to rotate? Is it based on temperature of the oven or based on day/time? If day/time, what was your source to determine rotating based on time?

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My day job is looking at the market for electric vehicles and related infrastructure. I'm a postdoc at the University of California Davis. I do maker projects in my free time.

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