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Making Yoghurt with a Portlet

An Arduino based programmable outlet with screen and thermocouple inputs for implementing a wide range of awesome projects !

Portlet (4)

KICKSTARTER PAGE: http://kck.st/1xuz7Ev

A portlet is an Arduino based programmable outlet with screen and thermocouple inputs for implementing a wide range of awesome projects !

The Portlet project began when the designer attempted to make his own yoghurt.  But he quickly realized it could be an extremely versatile tool with a tons of different uses, so he transformed it into a legitimate product.


Portlet plugs into a standard Nema 15 style wall outlet and is controlled by an Arduino brain.  It features:

  • Two outlets on the front for plugging in devices.  These are controlled by relays to turn them On or Off.
  • Two thermocouple inputs for monitoring temperatures.
  • 4 buttons which can be programmed for … whatever you like.
  • 1 LCD screen to display happy messages and thought provoking comments about your project.
  • Access to the programming pins of the Arduino (currently the Arduino Pro from the good folks at Sparkfun)


There are a ton of uses for a device that can monitor temperature and/or control some outlets.  For example, using the Portlet and a crockpot you immediately have both a yoghurt incubator, a pasteurization tool (for yoghurt, cheese, home brewing, etc.), or a sous-vide cooker!

cooker control with portlet
Using Portlet with a Crockpot

Other uses:

  • Timer for your soldering/curling/clothing/whatever-hot-device.  Then there is no more worried about “did I leave that on” because it will turn off automatically after a set period of time.
  • Monitor the temperature of your pipes and make turn on a heater so they don’t freeze.
  • Make a connected outlet; after all it’s pretty easy to plug in a Bluetooth or zigbee module!

For more information: check out kickstarter page.

The basic steps in making yoghurt are:

  •  Heat the milk to 185 degrees F.
  • Pasteurize the milk (185 degrees F for 30 minutes)
  • Cool the milk down to 110 degrees F.
  • Pitch the yoghurt culture and let it culture around 100 degrees for 7 hours
  • Put your yoghurt in the fridge!

To achieve this we’ll use the following

–   A Portlet. This will be the primary controller for the whole operation.

–    A crockpot. Standard issue kitchen fare. Located in GoodWill stores all over, and can even be purchased for brand new at very reasonable prices.

–    Milk. Any milk will do. If you want non-fat yoghurt, you should start with non-fat milk. If you want tasty, creamy yoghurt, it’s best to start with whole milk.

–    Yoghurt. Pick a brand that you want to try and copy. This will provide your starter culture for all the little bacteria. Use a new cup if possible; you want to minimize the chance of introducing foreign bacteria into your culture. Only a spoonful is necessary.

Programming the portlet:

Before you start, it’s best to get the Portlet all ready and programmed. The Portlet is based on the popular Arduino platform and uses the Arduino IDE for programming. Here we give a brief example of how to program the Arduino, so if you want to learn more you should head over to the excellent Arduino home page at http://www.arduino.cc/

First off, plug in your programming cable into the programming interface of the Portlet. The interface is the six header pins coming off of the Arduino Pro Mini build into the device. There is an access port in the covers on the right side of the Portlet. If you are using the Sparkfun 5V programming cable, the black wire goes on top for the correct orientation.


Open up the Arduino IDE and copy and paste the Yoghurt Sketch Program attached into the IDE.

arduino 1

Make sure you have the correct serial port selected for your interface and for the board choose the “Arduino Pro or Pro Mini (5V, 16MHz) w/ATmega328”.

arduino 2

arduino 3

Arduino program is on the “Programming” tab. Check out the program at Github.

The Set up:

Here you see the crockpot plugged into the Portlet, which in turn is plugged into the wall outlet. The milk (raw Claravale milk is shown) and the yoghurt are on hand. The milk will get poured into the crockpot right away but since you won’t be needing the yoghurt for some time, you should keep that in the fridge until ready.

The program supplied below expects that you are using Outlet 1 and Thermo 1. Make sure you have the crockpot and the thermocouple plugged into the right sockets!

set up

Defining the temperature curve:

If we are to graph this process, the basic temperature profile looks like:

pitch curve

And a more detailed explanation of the steps would be:

  1. Here we are trying to get to 185 as quickly as possible. Depending on your crockpot, this curve may look different; steeper or more shallow. That’s okay. We aren’t really concerned with how quickly we get there, we just want to spend some time at 185 to make sure the batch is pasteurized and maybe we’ve broken down the proteins a little bit.
  2. Now we spend some time at 185. The code for maintaining the temperature is very simple but adequate for this purpose. Ten minutes at 185 is recommended to make sure pasteurization is complete, but some yoghurt manufacturers will actually hold it there much longer to get a creamier yoghurt. It’s a good place to experiment !
  3. Now that pasteurization is complete, we want the temperature to go down to about 110 so we can start the culturing process. Some people will take their pot of milk and put it in ice because they don’t want to wait around forever. But since the Portlet is automating this whole process, we can just let it turn the crockpot off and wait until the desired temperature has been reached. With the program attached it will notify us that it has arrived there by flashing the backlight on the LCD screen. This indicates it is time to dump a few spoonfuls of yoghurt into the pot and start the culturing process.
  4. Culturing bacteria is very simple. You’ve given it a clean environment without any competition by pasteurizing the batch and it has plenty of nutrients in the mil, so now all it wants is a warm place to do its’ thing. So we set the Portlet to maintain a temperature of about 110°F and let it sit for about 7 hours. The Portlet has a timer that counts down the time and notifies you when that time has elapsed. Once that time is over, you have yoghurt!
  5. We don’t want to let the yoghurt sit and culture forever so at this point we’ve turned off the heat and are letting the batch cool down to room temperature. This will not stop the culturing process, but the colder temperature will at least slow it down. By now you should have put the yoghurt into the fridge. The Portlet does not have the ability to do that for you (not yet anyways…)

Make Yoghurt!

Now let’s get started!

1) Fill the crockpot with milk.

As much milk as you put into the crockpot is how much yoghurt you’ll have the end. Since you are probably reading this because you really like yoghurt, go ahead and fill it up !

2) Position everything

The crockpot will be taking up some counter space for a few hours so make sure it’s somewhere out of the way. Make sure the crock pot is turned on to high. The Portlet will be controlling the temperature by turning the outlet on or off, but it can’t turn the crockpot on for you !

Then make sure the end of the thermocouple is sitting in the milk. That’s the only way it will be able to get a nice temperature reading.

3) Start !

Follow the prompts on the LCD screen of the Portlet. It will tell you to hit button 1 (the one on the left) to get started.

It will then heat the milk up to 185, displaying the temperature along the way. Then it sits at 185 for the set period of time, displaying the number of minutes. Then it cools down 110 displaying the temperature along the way.

4) Pitch the yoghurt!

Once at 110, it will notify you that it is time to “pitch” the yoghurt. This is a fancy way of saying that you should now dump a few spoonfuls of yoghurt into your batch. Then hit the button to tell Portlet you are ready to start timing.

For the culturing period, the Portlet will maintain a nice culturing temperature while displaying the number of minutes.

5) Refrigerate your yoghurt!

After culturing, the yoghurt is ready to eat! But it’s not very good warm. So you should probably stick it in the fridge for a while first.

Reference and yoghurt making instructions at: www.makeyourownyogurt.com

Portlet (1) Portlet (2) Portlet (3) Portlet (4) Portlet (5) Portlet (6)

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