Introduction: Sous Vide Oven Controller

About: I specialize in electronics, but I can operate a band saw, ride a skateboard, and brew a tasty cuppa. I blog incessantly.

Instead of cutting apart a perfectly good Crock Pot this build will show you how to build a controller your appliance you can plug into. This modular approach means you do not need to buy a second appliance. If you have an old rice cooker in the cabinet you can make it a sous vide oven.

The tricky part of sous vide cooking is keeping the water at a precisely regulated temperature. Most cooking appliances have the ability to turn the heat down but regulating it with any accuracy is not possible without automation. Fortunately temperature controllers are not expensive and they are as easy to use as a regular oven. An eBay search for temperature controller 58 194 should give options under fifteen dollars ($15USD). Amazon also has the same controllers. The advantage these devices have over a dial on the side of a slow cooker is that the temperature controllers use a thermometer to monitor the temperature.

The versatility of these controllers is also impressive and since this build is being made very modular it is possible to use this appliance for things other than cooking, such as automating a window fan. A short list to get the brain gears turning is shown at the end of the instructions.

The goal of these instructions is to help you build a device that is highly functional, rugged, and looks good on your counter. All the wires are hidden away and sealed up so a few errant splashes from the sink are not cause for an emergency.


  • Temperature controller. eBay. Amazon.
  • Slow Cooker*
  • Old computer power cord*
  • 6x6x4 PVC enclosure*
  • Duplex receptacle
  • Receptacle cover
  • Cord-tight connector
  • Electrical lock nut for cord-tight connector
  • Thermometer for comparison
  • 3.5mm plug, mono
  • 3.5mm jack, mono
  • Small wire whisk
  • 2 #8 nuts
  • Shrink tubing 3/32inch diameter
  • Wire nuts. Preferably lever locking nuts
  • Electrical tape
  • Solder
  • Timer
  • Wide masking tape
  • 100% silicone sealant

*Alternatives to these devices are given on the last page

Step 1: Electrical Cable Preparation

The PVC enclosure will have three holes. The easiest to cut is the 7/8 inch hole for the cord-tight connector. The second easiest to cut is a rectangular hole for the receptacle. The most difficult to cut is the rectangular hole for the temperature controller.

  1. Cut and strip the electrical cord so that there are three exposed and stripped wires on one end and a plug on the other end
  2. The wires should be black, white and green
  3. If they use different colors identify them as HOT, NEUTRAL, and GROUND
  4. Put the cord-tight connector on the cord eight inches from the stripped end
  5. It should be facing so the rubber seal is closer to the plug end than the stripped end
  6. Tighten the cord-tight connector onto the cord
  7. If necessary, bulk up the wire by wrapping it with electrical tape

Step 2: Power Cord Entry

The only hole drilled into the base of the enclosure is to let the electrical power cord into the box. I like to keep this cord coming out the back of the enclosure so it is hidden but it also makes sense to have it come out the side so the control box can be pushed up against a wall while cooking.

  1. Measure half way across the PVC enclosure
  2. Measure 1-1/2 inches up from the bottom
  3. Pilot a hole at the intersection
  4. Drill a 7/8 inch hole
  5. Insert the cord-tight connector
  6. Tighten the electrical lock nut from the inside of the enclosure

Step 3: Receptacle Hole

The holes in the enclosure lid are marked and cut from the inside so all the scratching and abrasions from the tools are on the inside and not visible once the unit is sealed up. The hole for the receptacle should not be a stressful step because the receptacle cover will be large enough that any imperfections will be hidden. The most important thing is to make sure the receptacle is squared up to the edge of the enclosure lid. A crooked receptacle will look sloppy more than a few scratches.

  1. Put down some wide masking tape on the inside of the enclosure lid
  2. Lay the receptacle cover face down against the lip of the enclosure lid
  3. Align the receptacle cover so it is centered on the enclosure lid edge
  4. Trace the holes of the receptacle cover onto the tape
  5. Draw a rectangle 1/4 inch[6mm] larger on each side around the marked area
  6. Keep the rectangle square with the enclosure lid
  7. Draw a second rectangle 1/2 inch[12mm] smaller on each side
  8. Make divots at the corners of the smaller rectangle
  9. Drill pilot holes through the divots
  10. Drill the holes out to 1/2 inch[12mm] diameter
  11. The holes should occupy the corners of the receptacle but not be exposed by the sides of the cover
  12. Cut out the plastic between the holes
  13. Position the receptacle in the rough hole
  14. Square it up with the edge of the enclosure lid
  15. Mark the locations of the receptacle mounting holes on the lid
  16. Drill to 11/64 inch[4.5mm]

Step 4: Temperature Controller Hole Part One

The hole for the temperature controller is the trickiest step in this project. Any large imperfection in the hole may become visible around the lip of the controller face. Sloppy measurements will be the most obvious with this hole. Be careful when using a saw on this hole because a line that is not true may be an eyesore later. Give yourself as much time as you need to do this step neatly.

Option 1

  1. Print the attached PDF at 100% scale
  2. Align the template to the inside of the enclosure lid using the spaced lines
  3. Tape the template in place when it is square to the edges and suitable distance from the edge
  4. Use the line closest to the cut-out region when using the 6x6x4 enclosure
  5. Use best judgment when using an alternate enclosure
  6. Make divots at the holes outlined

Option 2

  1. Apply wide masking tape to the inside of the enclosure
  2. Draw a lengthwise rectangle 2-3/4 inch[70mm] by 1-1/8 inch [29mm] one inch from the edge of the enclosure lid
  3. Shrink the rectangle 1/2 inch [12mm] on each side
  4. Make divots on the corners of the smaller rectangle

Step 5: Temperature Controller Hole Part Two

  1. Drill 1/2 inch [12mm] holes into the divots
  2. Use a saw to cut away the space between the holes and make a rounded edge rectangle
  3. Use a saw to square off the corners
  4. Square up the cuts for true lines
  5. Remove the plastic clips from the side of the temperature controller
  6. Make sure there is a good fit for the temperature controller
  7. Insert the controller into the face of the enclosure
  8. Install the plastic clips on the side of the temperature controller
  9. The top of the display should be next to the receptacle hole

Step 6: Electrical Wiring

A quick couple of notes about wiring. I have a diploma as a Construction Electrician so I have training and experience with wiring. If you do not feel comfortable wiring ask for help. The second note is an anecdote from those college days. My electrician teacher would identify amateurs who tried to do their electrical work by how much wire slack they afforded themselves in the boxes. Amateurs would only give themselves a few inches to conserve a precious scraps of wire. Electricians would pull a generous amount into the electrical box and give themselves enough to work with and to have some extra for the future. He charged stingy amateurs more because it was a hassle. Lesson: give yourself enough wire inside the box.

  1. Observe the electrical diagram sketch
  2. Break off the tab between the darker bolts
  3. Follow the schematic or look closely at the picture which shows all the wires
  4. The wire for the inside of the box can be salvaged from the cord being used for this project
  5. It may help to read the literary connection list
    1. Common wire, white, was hooked to:
      1. Terminal 4 on controller
      2. Silver bolt on receptacle
    2. Line wire, black, was hooked to:
      1. Terminal 3 on controller
      2. Terminal 2 on controller
      3. One brass bolt on receptacle
    3. Ground wire, green was hooked to the grounding lug on receptacle
    4. Terminal 1 on the controller was hooked to the other brass bolt of the receptacle
  6. Fasten the receptacle so the support feet rest on the outside of the enclosure lid
  7. Put the bolts through the holes drilled for them
  8. Finger tighten the #8 nuts
  9. Make sure the receptacle is true to the edge
  10. Tighten the #8 nuts all the way
  11. If someone can check the wiring have them do so
  12. Put the cover on the receptacle
  13. Plug in the device
  14. It should display LLL
  15. One outlet should have power. This can be tested by plugging in a lamp to see if it turns on

Step 7: Thermometer Protection

To keep the thermometer off the heated bottom and away from cool food it has been enclosed in a small stainless steel whisk. The whisk is a great shape since water can freely flow through the tines without obstruction. Strictly speaking it is not necessary but since precision is the name of the game it is recommend to keep the thermometer probe protected.

  1. Grasp the metal disk of the whisk with pliers
  2. Drill a pilot hole in the center of the disc
  3. Drill the hole out to 3/16 inch [5mm]
  4. Pass the thermometer through the hole into the head of the whisk
  5. Hold the thermometer lightly with tweezers or pliers
  6. Apply a generous amount of silicone to keep the disc in place and the thermometer in place
  7. Take care to keep the silicone off the tip of the thermometer
  8. Allow the silicone to dry according to silicone directions

Step 8: Thermometer Connection Outside the Box

The NTC (Negative Temperature Coefficient) thermometer is not a polarity sensitive device which means it cannot be hooked up backwards. The wires on the temperature probe may need to be clipped and stripped so that wire are able to be soldered. These instruction makes the assumption that the builder knows how to solder. If not, there are many fine tutorials and YouTube videos which can assist.

  1. Clip away any terminals which may be on the thermometer wire
  2. Strip the wires if they are not already
  3. Tin the wires if they are not already
  4. Tinning means to coat the exposed wire with a layer of solder
  5. Disassemble a 3.5mm phono jack
  6. Place the wire through the shell
  7. Put a short piece of heat shrink tubing on each wire
  8. Solder one wire to each of the two terminals of the 3.5mm phono jack
  9. Slide the heat shrink tubing over the solder joint
  10. Use a heat source to shrink the tubing
  11. Screw the shell into place

Step 9: Thermometer Connection Inside the Box

The modularity of the project will hopefully give people other ideas for how to use this controller. All kinds of home automation is based on temperature sensing. It is possible to hook up a different NTC thermometer using the 3.5mm jack and have a different application altogether. One temperature probe could go outside to see what the temperature is outside and turn on a light bulb when there is a risk of the garden being frostbit.

  1. Drill a 5/16 inch [8mm] hole next to the left side of the temperature controller
  2. Placement is not critical
  3. Strip the ends of two small wires 8 inch [200mm] long
  4. Tin the ends
  5. Put a short piece of heat shrink tubing on each wire
  6. Solder one wire to each of the two terminals of the 3.5mm phono socket
  7. Slide the heat shrink tubing over the solder joint
  8. Use a heat source to shrink the tubing
  9. The other ends of the wire go into the NTC terminals of the temperature controller
  10. Tighten the screws of the temperature controller
  11. Push the receptacle of the 3.5mm socket through the 5/16 inch [8mm] hole
  12. Glue the 3.5mm socket in place
  13. Put the lid on the enclosure
  14. Screw the lid down securely

Step 10: Testing

At this point the unit is ready for testing. Since the temperature controller does not use a digital thermometer it is possible that the readings may not be 100% accurate so it is important to verify the readings against an accurate thermometer. If the temperature controller allows the water to remain too cool when cooking food may be undercooked and hazardous. If this is the case it would be prudent to make a note of how much hotter the oven should be set in order to maintain sufficient temperature.

A note about how the temperature controller works. The relay closes when the temperature is below the set point then opens when the desired temperature is reached. If the temperature falls below two degrees of the set point the relay closes again and remains closed until the desired temperature is reached.

  1. Plug the 3.5mm jack into the 3.5mm socket
  2. Power up the temperature controller by plugging it into the wall
  3. Plug a lamp into the switched outlet
  4. Experiment by putting the thermometer into different temperatures of water, ice water, hot water, and tap water
  5. Watch the behavior of the lamp as the temperature controller compensates for the changes in temperature
  6. Compare the readout to a reliable thermometer
  7. Make a note if the oven needs to be set to compensate for discrepancy
  8. Now is the time to test the oven by actually cooking something. Eggs are a good place to start, if you eat eggs, because they are inexpensive and cook quickly
  9. Sous Vide Supreme recommends that soft boiled eggs be cooked for fifteen minutes at 167ºFahrenheit
  10. The egg yolk should be thick and the egg whites should be slightly solidified

Step 11: Closing Thoughts and STUFF

This unit can be used for other automation projects in the home. It can heat a room with a space heater or cool a room with a fan whenever it is temperate outside. It could be used to control an alcohol still but check your local laws first. I think it is legal to distill alcohol if it is ONLY used to power vehicles but better check just to be safe.

  • Alternative use for controller
    • Still controller
    • Cooling fan for window
    • Space heater controller
    • Frost alert

Alternatives to some of the devices used in this example

  • Alternative to small slow cooker**
    • Rice cooker
    • Hot plate with an appropriately sized pot or kettle
    • Oven roaster filled with water
  • Alternatives to mini whisk
    • Large whisk
    • Single blender blade
    • Large diameter compression spring
    • Tea ball
    • Tea spoon
  • Alternative to 6x6x4 PVC enclosure
    • Wooden box
    • Rubbermaid tote
    • Handy box with receptacle next to controller
    • Mount directly in or on a cooker
    • ABS enclosure
    • 3D printed enclsoure
  • Alternative to 3.5mm plug and jack
    • Direct wire
    • 2.5mm plug and jack
    • Molex connector
    • 0.1 inch spaced header pins
    • RJ11 plug and socket

**Whatever device is selected it needs to have simple controls. Analog controls, often the less expensive model, are compatible with this controller. To test, plug in your appliance and turn it on, it should get warm. Unplug the device for a few seconds and plug it back in, if it continues to heat without touching the controls again it will work with this controller. The reason is that the temperature controller cuts all power to the device and digitally controlled devices will lose their memory.

This build took me less than fourteen days and almost that many trips to the hardware stores and thrift stores. I was inspired by other people and their builds but I did not like the enclosures they chose. Some people had the temperature controller sitting on the counter while a water bath was inches away. Please do not do that. An enclosure is less than fifteen dollars and an ambulance ride is more expensive.

I run a blog where I talk incessantly about the things I build, including an unabridged version of this project where I talk about all the things I did wrong as well as what I did right and what I plan to do with it after the build. There is also a day I talk about how to calibrate the thermometer to get very accurate readings from these inexpensive controllers. There are other neat things there like a device that lets you hear temperatures and a keyboard you can use from inside your pockets.

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