Diy wireless pH-meter

In cheese-making, the key to a tasty, and reproducable, cheese, is keeping track of the  exact pH and the temperature in the active culture. You can do this with manual tools, such as a kitchen thermometer and pH-strips, but the measurements will be crude, and depend on your constant presence. That leading to inconsistencies between batches,  and difficulties in tracking errors in the process.

Michel Lepage is cutting the curd. Photo taken at the craft cheese-making course we took at Eldrimner in 2014.
A digital pH-meter is expensive. You can find some from €100, but you wont get built-in temperature correction for less than €250, and wireless goes beyond €350. For continous readings and  the possibility to recalibrate your sensor yourself, instead of sending it to the manufacturer,  add a lot more… I havn’t yet found a device capable of tweeting its readings 😉

My diy pH-sensor is not exactly cheap either. It ticks in at about €150 in material costs. I’ve seen people look pensive when they see the casing, and subconsiously push it closer to the recycling, so a slightly pricier casing than the pet bottle might be an investment. Otherwise, the bill of materials looks like:

Sensor

  • Atlas pH meter kit $149 (EZO version)
  • Arduino mini pro 3.3v $1.90
  • NRF24L01 radio $1
  • DS18B20 waterproof temp sensor $1.63
  • Battery holder $3
  • 2xAA batteries
  • Cables

With todays exchange rates, it translates to around €150.
If you’re setting up a new sensor network, you need a radio gateway and a computer to run the controller software on too

  • Arduino nano $6
  • NRF24L01 radio $1
  • Cables
  • Old computer or raspberry pi $25-$50

      You can order everything from ebay or aliexpress through the Mysensors store, but the items listed there may not always be availible in singel packages. Anyway, you will need more of those radios.

      Shipping is usually free from China (who is paying that?), but the pH-kit comes from the US, so add a few euros for shipping and customs.

      Features:

      • Measures pH-level in fluids and semi-solid compounds.
      • Calculates the correct pH from the latest temperature reading.
      • Measures temperature
      • 30 seconds between samples.
      • Continous measuring, just leave the probe in the milk and watch the readings.
      • Wireless transfer of data to the raspberry pi based controller unit
      • Presents the readings as a datastream or in nice graphs in a web interface. Use your phone or tablet to monitor the process from anywhere.

          Prerequisites:

          Tools

          • FTDI USB programmer, to program the arduino  mini pro and perform calibration. If you use arduino nano instead, you can skip this, but the nano is more expensive and power consuming.
          • Soldering iron, lead, soldering paste.
          • Computer with arduino ide or codebender running.
          • Pliers, knives, screwdrivers and that kind of stuff.

          Skills

          • Basic soldering. The only soldering done in my prototype is on the on/off switch. For a sturdy and reliable device to use in a kitchen environment, I recommend soldering the connections rather than using Dupont cables.
          • Basic programming. You can clone my code from codebender and hope it will work out of the box, but since things changed quickly on the internets of things, you will probably need to change some code to adapt to new version etc. So some understanding of coding will be helpful.
          • Arduino/MCU experiences. I wouldn’t recommend to make this your first microcontroller or Mysensors project. Start out with a simple blinking light and then a temperature sensor to make sure you get the IDE and Mysensors API.
          • Raspberry pi/Linux experiences. You could use a Windows computer as controller and user interface server, but if you’re up to arduino hacking, you might as well use an embedded device right away.

          First experiences with cover crops

          Since we have quite much old straw occupying the hay loft, and the maple on the frontyard is producing a great amount of compost material each fall, we decided to try to grow some potatoes in that biomass.

          The straw and leaves where put directly on the Ground in early april, as the potatoes where put to germinate inside the house. Four weeks later, when the risk for nightfrost had diminished, the potatoes where scattered on the strawbed, covered with more straw and leaves, and watered.

          As comparison, a few potatoes where planted using the traditional methodologies of digging them into the ground.

          The first harvest was expected 8-10 weeks after germination (middle of june), but a chilly period in may delayed it with two weeks. Maybe the cover crops method is more suspectible to cold weather since it lacks the isolating features from a thick layer of soil? We don’t know, since the soilgrown potatoes is a later kind. That’s a parameter to keep track of next year.

          Reflections:

          Strawbed:

          • Potatoes can be harvested continuously. You don’t dig up the plant, just follow the stem and roots in the straw and collect the right sized potatoes. Smaller ones are left to grow some more.
          • The potatoes are very clean, and probably free from contamination from soil bacterias.
          • No digging required.
          • Vandalizing snails was a great concern, but turned out to be a minor problem. They seem to prefer occuring weeds like dandelions to the potato leaves. The patches with less weed were more affected by snails than wilder ones. However, young plants attacked by snails had a tougher time reaching full growth, but the harvest from them was only delayed, not diminished. Leaving mature potatoes in the ground for too long made them a decent meal for the snails, so the advice would to pick the big ones continuously.
          • Some kind of radar device would be handy in finding mature potatoes in big scale cultivation.

          Soil:

          • Since the potatoes where left in the soil to let more of them grow big before harvest, more potatoes were damaged by snails.
          • Manual labour is tougher with the soilbed. Breaking the ground (well, we did some of it with tractor and harrow), covering with soil, digging up the harvest.
          • The potatoes are dirty, but the dirt may work as protection and keep humidity in the storage. We’ll see.
          • Smaller harvest, since the plant gets damaged when the potatoes are dug up.
          Cover crops potatoes

          The need for watering seems to be the same with both methods. The strawbed was very moist in the lower layers, even after several weeks of draught. We watered both patches quite much after putting out the potatoes.

          Neither patch has shown any signs of leaf rot. An hypothesis yet untested is that growing mushrooms among the potatoes would make it harder for leaf rot to establish. The mushrooms didn’t thrive in the heat, so we’ve prepared a mycelium to mix in the strawbed in the autumn.
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