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==Thermometer== Why thermocouples (TC) vs. another type of sensor? It depends on your application! TCs can be very robust, for nasty environments and super high temperatures, but their voltage is very small so they may require an amplifier with digital out (http://www.sparkfun.com/products/307, $12 - see also http://www.chinwah-engineering.com/USBThermocoupleProject.html). Other types of sensors (like DTS) may not be as rugged, but in the end they may be sufficient for bioprojects if the sensor is protected, and the total cost may be less ($4). If we can hack thermocouples well enough to make them cheap, there are some advantages, it just depends on the application whether they are worth it! Commercial thermocouple "probes" are available from approx. $20 upwards *[http://www.omega.com/ppt/pptsc.asp?ref=HTTC36 Hollow Tube Thermocouple Probe] $19 And we can use just the thermocouple wire to create our own, buying it by the foot from places like McMaster Carr [http://www.mcmaster.com/#type-k-thermocouple-wire/=bkaksl, both wires in a sheath for ~$1/foot, by the foot] or Omega (bare wire is here http://www.omega.com/ppt/pptsc.asp?ref=SPIR&Nav=temh02). Omega is the ultimate source, but they seem to only sell it by the roll (25 foot minimum, buy both wires separately) or in the form of super nice manufactured probes ($). Charlie has access to a good amount of Type K metal sheathed TC wire, plus assorted probes and a TC reader he can donate - as we go along our improving expertise will lead us to resources other people can use... like the relatively cheap McMaster Carr wire. There is also a somewhat sketchy [http://www.instructables.com/id/Making-A-Thermocouple/ Instructable] for how to build one - at approx. $15, it’s not going to be much cheaper, though, so choosing the DIY version would be mostly for the educational benefit of actually building it (almost) from scratch. This soldering method will work with the Omega wire, and better junctions can be made with a welder or capacitive discharge. Presently have a prototype thermometer which uses a one-wire device: [http://www.hacktronics.com/Sensors/Digital-Temperature-Sensor-DS18B20/flypage.tpl.html DS18B20 digital temperature sensor, DTS - $4, also from Sparkfun] - it's not talking to my Arduino yet, but it will. Oh, yes...it will. (Rikke) The digital temperature sensor (DTS) is indeed a good one to start with - inc. because one is already mounted in a probe. We'll need to test that probe to see what its sensitivity and accuracy is (rough probes can have a problem with response times, but in many cases the temperature does not change quickly in bio systems), but having a sensor that does not need auxillary electronics (like the TC does) ready is a big plus. http://www.danielandrade.net/2008/07/05/temperature-sensor-arduino/, http://www.instructables.com/id/Waterproof-a-LM35-Temperature-Sensor/ The thermistor has some advantages over other sensor types in that it is inexpensive to get started with (<$2 for bare sensors, even $.25 - almost disposible), the electronics and communications are simple, and it is easily available in a wide variety of sensor/probe designs. Here is an easy source (http://www.hacktronics.com/Sensors/Thermistor-Temperature-Sensor/flypage.tpl.html) but note they tend to be rated only up to the boiling point of water - reasonable for a bio based measurement system, but no further. They also offer advice on monitoring one with an Arduino (http://www.hacktronics.com/Tutorials/arduino-thermistor-tutorial.html), including software and the same is generally true for the DTS - we are building on the experience of others. Thermistors and thermistor probes are available everywhere (I got the one for my old distiller from Radio Shack, but they may not offer them anymore), including Jameco and Digikey (so many it can be confusing. It seems like the 10kOhm version is the one to standardize on, but we can discuss. We can calibrate/troubleshoot it with the thermocouple reader we now have. Thermistors are also common for the temperature compensation of pH sensors. What shall our specifications be? Range of temperature, resolution, accuracy, response time, precision (repeatability), cost, durability, calibration potential, etc. We have the same need for all of our sensors, requiring us to somewhat anticipate what users will do with our board. :Biologically relevant temperature range is approx. 0-100°C; accuracy should not be less than ±0.5°C at 25-35°C. pH range is (1-14), and required precision is approx. ±0.5, preferably better. dO probe should be able to measure % conc. with an accuracy of approx. ±2%, preferably better. :Concerning sensor validation: We have a pretty accurate digital body thermometer and commercial thermocouples for the thermometer. Should we choose to build a pH meter, we can easily get fairly accurate pH strips, and also borrow a 'proper' pH meter through Sean. Same applies for the dO probe, and getting a sample run through a spectrophotometer shouldn't be impossible either. No. of living cells in a suspension (Colony Forming Units pr. volume, CFU/mL) can be measured by plating a diluted sample on a petri dish and counting the no. of colonies formed, then calculating backwards to the original cell density. Can we get petri dishes, some pre-hopped DME and some agar from some of our brewing contacts? /[[User:Rikke|Rikke]]
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