A Compensated Thermocouple Amp, Ready for Arduino

When you want to measure temperature with an Arduino or other microcontrollers, there are a ton of options for sensors. Temperature chips and sensor modules abound, some with humidity sensors built-in and all with easy interfacing and an expansive supporting code library. But dip one of those sensors into, say, molten aluminum, and you’ve got a problem.

If you’re measuring something hot, you need a thermocouple. Trouble is, the signal from a thermocouple is pretty small, and needs amplification and compensation before being fed into the ADC of a typical microcontroller. Unable to find a commercial amp to meet his needs, [MonkHelios] built his own thermocouple amp for microcontrollers. The design is centered around an LTC2053 instrumentation amp, which does the job of converting the K-type thermocouple’s 40.6μV/°C output to a nicely scaled 10mV/°C range, just right for ADC consumption. He also thoughtfully included an LT1025 cold-junction compensator; thermocouple amps are referenced to 0°C, so the compensator measures the actual temperature of the cold end of the junction and scales the output accordingly. The whole amp is nicely laid out on a DIY single-sided PCB with meticulously applied solder mask — this is one of the nicest home-etched boards we’ve seen in a long time.

[Bil Herd] designed a similar thermocouple amp not too long ago himself, so you might check that out too.  Or maybe you need the basics of instrumentation amps? Our “Beyond Measure” series will get you started.

PID Controlled Charcoal BBQ – Put an Arduino on it!

At Maker Faire Milwaukee this past weekend, [basement tech]  was showing off his latest build, a PID controlled charcoal grill. While it hasn’t QUITE been tested yet with real food, it does work in theory.

PID (a feedback loop with some fancy math used to adjust the input to get a consistent output) controlled cooking is commonly used for sous vide, where one heats up a water bath to a controlled temperature to cook food in plastic bags. Maintaining water temperature is fairly easy. Controlling a charcoal barbecue is much more difficult. [basement tech] accomplishes this with controlled venting and fans. With the charcoal hot and the lid on, there are two ways to control temperature; venting to let hot air out, and blowing air on the coals to make them hotter. A thermocouple sensor stuck through the grill gives the reading of the air inside, and an Arduino nearby reads that and adjusts the vents and fans accordingly.

The video goes into extensive detail on the project, and describes some of the challenges he had along the way, such as preventing the electronics and servos from melting.

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Brasilia Espresso Machine PID Upgrade Brews Prefect Cup of Energy

Coffee, making and hacking addictions are just bound to get out of control. So did [Rhys Goodwin’s] coffee maker hack. What started as a little restoration project of a second-hand coffee machine resulted in a complete upgrade to state of the art coffee brewing technology.

coffee_hack_arduinoThe Brasilia Lady comes with a 300 ml brass boiler, a pump and four buttons for power, coffee, hot water and steam. A 3-way AC solenoid valve, wired directly to the buttons, selects one of the three functions, while a temperamental bimetal switch keeps the boiler roughly between almost there and way too hot.

To reduce the temperature swing, [Rhys] decided to add a PID control loop, and on the way, an OLED display, too. He designed a little shield for the Arduino Nano, that interfaces with the present hardware through solid state relays. Two thermocouples measure the temperature of the boiler and group head while a thermal cut-off fuse protects the machine from overheating in case of a malfunction.

Also, the Lady’s makeup received a complete overhaul, starting with a fresh powder coating. A sealed enclosure along with a polished top panel for the OLED display were machined from aluminum. [Rhys] also added an external water tank that is connected to the machine through shiny, custom lathed tube fittings. Before the water enters the boiler, it passes through a custom preheater, to avoid cold water from entering the boiler directly. Not only does the result look fantastic, it also offers a lot more control over the temperature and the amount of water extracted, resulting in a perfect brew every time. Enjoy [Rhys’s] video where he explains his build:

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PCB Laminator Is Its Own Project

One of the easiest ways to make PC boards at home is to use the toner transfer method. The idea is simple: print the artwork using a laser printer and then use a clothes iron to transfer the toner from the paper to a clean copper clad board. The toner is essentially plastic, so it will melt and stick to the board, and it will also resist etchant.

There are several things you can do to make things easier. The first is the choice of paper. However, the other highly variable part of the process is the clothes iron. You have to arrange for the right amount of heat and pressure. If you don’t do a lot of boards, you’ll probably have to make several passes at getting this right, scrubbing the reject boards with acetone and scouring pads to clean them again.

[Igor] had enough of the clothes iron and knew that other people have used lamination machines to get the toner off the paper and on the blank board. He started with a commercial laminator but hacked it for PID control of the temperature and made other improvements.

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A Wireless Wood Stove Monitor

[Michel] has a wood stove in his basement for extra heat in the winter. While this is a nice secondary heat source, he has creosote buildup in the chimney to worry about. [Michel] knows that by carefully monitoring the temperature of the gases in the chimney, he can hit the sweet spot where his fire burns hot enough to keep the creosote under control and cool enough that it doesn’t burn down the house. To that end, he built a wireless wood stove monitor.

The first version he built involved an annoying 20 foot run between the basement and living room. Also, the thermocouple was mounted on the surface and made poor contact with the chimney. Wood Stove Monitor 2.0 uses a probe thermometer on an Exhaust Gas Temperature (EGT) thermocouple to measure the temperatures. The intel is fed to a thermocouple amplifier to provide a cold-compensation reference. This is shielded so that radiant heat from the stove doesn’t compromise the readings. An nRF24L01+ in the basement monitoring station communicates with another module sitting in the living room display so [Michel] can easily find out what’s going on downstairs. When it’s all said and done, this monitor will be part of a bigger project to monitor power all over the house.

Interested in using a wood stove to help heat your house? Why not build your own?

I am a Battery: Harvesting Heat Energy

If you get tired of charging batteries, you might be interested in [Hackarobot’s] energy harvesting demo. He uses a peltier device (although he’s really using it as a thermocouple which it is). A 1 farad super capacitor stores energy and an LTC3108 ultra low voltage converter with a 1:100 ratio transformer handles the conversion to a useful voltage.

The truth is, the amount of energy harvested is probably pretty small–he didn’t really characterize it other than to light an LED. In addition, we wondered if a proper thermocouple would work better (some old Russian radios used thermocouples either in fireplaces or kerosene lamps to avoid requiring batteries). Although a Peltier device and a thermocouple both use the Seebeck effect, they are optimized for different purposes. Thermocouples generate voltage from a temperature differential and Peltier modules generate temperature differentials from voltage.

However, as [Hackarobot] points out, the same technique might be useful with other alternate power sources like solar cells or other small generators. The module used has selectable output voltages ranging from 2.35V to 5V.

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Hacker Creates Thermal Probes by Welding with a PC Power Supply

[Illya Tsemenko] decided to build his own thermocouples from bare wire. [Illya] is interested in measuring the temperature of Liquid Nitrogen and for this he needed T-type probes. While you can buy these for about 20 bucks, he felt this was too expensive for what is essentially two pieces of wire and decided to build his own.

Thermocouples use the Seebeck effect, when a piece of metal is hot at one end, and cold at the other the electrons in the hot end will be more energetic and migrate towards the cold end, creating a voltage. While this migration occurs in single metal, it can’t easily be measured (as the voltage will be the same as the measurement point). For that reason thermocouples use two metals in which the migration occurs at different rates. This difference creates an overall migration in one direction, and a voltage can be measured which correlates to the temperature where the metals meet. Thermocouples are extremely common and have many applications.

In order to make his thermocouples [Illya] needed to weld the two metals together, and knocked together a quick welding rig using a PC power supply and graphite electrode from a powertool. The graphite electrode is important as it prevents oxidization during the welding process.

The process worked well, and [Illya] was able to make both K and T-type thermocouples and successfully measure temperatures down to -190 degrees C. Awesome work [Illya]!