Controlling a Hot Plate’s Temperature for the Lab

FCYCT1FHOKSCWXP.MEDIUM

When you need precise heating — like for the acetone polishing shown above — the control hardware is everything. Buying a commercial, programmable, controller unit can cost a pretty penny. Instead of purchasing one, try creating one from scratch like [BrittLiv] did.

[BrittLiv] is a Chemical and Biological Engineer who wanted something that performs well enough to be relied upon as a lab tool. Her design utilizes a plain, old hot plate and with some temperature feedback to run custom temperature ramps from programs stored on an SD card.

The system she developed was dealing directly with temperatures up to 338°F. The heating element is driven from mains, using an SSR for control but there is also a mechanical switch in there if you need to manually kill the element for some reason. An ATmega328 monitors the heating process via an MAX6675 thermocouple interface board. This control circuitry is powered from a transformer and bridge rectifier inside the case (but populated on a different circuit board).

She didn’t stop after getting the circuit working. The project includes a nice case and user interface that will have visitors to your lab oohing and aahing.

PID Controlled Glue Gun

Internals of a glue gun controlled with a PID controller

Hot glue falls into the same category of duct tape and zip ties as a versatile material for fixing anything that needs to be stuck together. [Ed]‘s Bosch glue gun served him well, but after a couple of years the temperature regulation stopped working. Rather than buying a new one, he decided to rip it apart.

With the old temperature regulation circuit cooked, [Ed] looked around for something better on eBay. He came across a cheap PID temperature controller, and the Frankengluegun was born.

A thermocouple, affixed with some kapton tape and thermal paste, was used to measure the temperature of the barrel. Power for the glue gun was routed through the PID controller, which uses PWM to accurately controller the temperature. All the wiring could even be routed through the original cord grips for a clean build.

Quality glue guns with accurate temperature control are quite pricey. This solution can be added on to a glue gun for less than $30, and the final product looks just as good.

Improved Thermocouples On A Microcontroller

ktype

If you’re reading a thermocouple with one of those fancy schmancy SPI thermocouple amplifiers, this one isn’t for you. If, however, you’re still going through those old-school analog thermocouple amplifiers like the AD595, [miceuz] has just the thing for you. He’s come up with a library for embedded devices that reads the temperature of a k-type thermocouple with +- 0.03°C of accuracy.

As with anything dealing with natural phenomena, the voltage generate by the bimetallic junction of a thermocouple probe is decidedly non-linear. This is a problem when dealing with embedded devices, as that would mean using floating point arithmetic, greatly increasing the amount of code. [micuez] found the NIST tables for a K-type thermocouple and interpolates the actual temperature of the thermocouple probe from the NIST data. The usual way of measuring thermocouples – a polynomial unction of some sort – has an error of about 0.06°C. [miceuz]‘s library has an error of less than half that, all while using less code.

The library doesn’t support temperatures below zero, but this is still a work in progress. Still, if you’re looking for a very accurate library for a forge, crock pot sous vide build, or a toaster  oven reflow controller, you can’t do better than [miceuz]‘s work.

Copper Oxide Thermoelectric Generator Can Light An LED

On Hackaday, we usually end up featuring projects using building blocks (components, platforms…) that can be bought on the market. We however don’t show many hacks that rely on basic physics principles like the one shown in the picture above.

In the video embedded below, [nylesteiner] explains that copper oxide can be formed when heating a copper wire using a propane flame. When two oxidized wires are placed in contact with each other, an electrical current is produced when one wire is heated much hotter than the other. The trade-off is that the created thermocouple generates a small voltage but a ‘high’ current. However, when you cascade 16 junctions in series you can generate enough voltage to light up an LED. Even though the complete system isn’t particularly efficient at converting heat into electricity, the overall result is still quite impressive in our opinion. We advise our readers to give a look at [nylesteiner]‘s article and blog to discover his interesting adventures.

 

[Read more...]

A Pair of Toaster Reflow Oven Builds

heater

For some reason or another, the Hackaday tip line sometimes sees a short burst of submissions for the same project. The latest one of these was for toaster oven reflow stations. They’re both great builds and different approaches to making a useful tool out of home appliances.

First up is [Richard]‘s build. he ended up with a fairly high-end build using a Rocket Scream Reflow Oven Controller Arduino shield. This shield accepts a normal K-type thermocouple and controls an external solid state relay with the Arduino’s PID library. [Richard]‘s build has a few neat additions – a properly dremeled enclosure, computer fan, and a welding blanket for insulation. Now that we think about it, it’s odd we’ve rarely seen any sort of insulation in these reflow oven builds.

Next up is [Ray]‘s version of a Black & Decker reflow oven. While not as fancy as [Richard]‘s build, this one does have a few features that make it very interesting. Instead of messing around with thermocouples, [Ray] simply took a digital kitchen thermometer – a neat tool that already a thermistor in a compact metal probe – and read the analog value with an Arduino. To control the power, [Ray] is using a cheap 433 MHz radio transmitter to control a few remotely operated power sockets. It’s a very clever and inexpensive replacement for a SSR, especially since [Ray] had these power sockets just lying around.

So there you go. The same tool, built two different ways. A great demonstration of how you can not only build anything, but you can build anything any way you want.

Thermocouple vacuum gauge teardown

thermocouple-vacuum-guage

We don’t know how [Ben Krasnow] gets his hands on so much cool hardware. This time around is a bit of vintage tech: a thermocouple vacuum gauge.

The part seen above, and represented in the schematic, is the sensor side of things. This is interesting enough by itself. It has an air chamber with an electric heater element in it. When air is present it dissipates the heat, when under vacuum the heat builds and causes the thermocouple to generate some voltage on its connections.

Keep watching his presentation and things get a lot more interesting. The original unit used to measure the sensor is a throwback to the days when everything had sharp corners and if you were running with scissors you’d eventually teach yourself why that’s not such a good idea. The designers were rather cavalier with the presence of mains voltage, as it is barely separated from connections grounding the case itself.

Want to see some of the other cool equipment he’s got on hand? How about a CT scanner he built.

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Building a tool to measure melting point

melting-point-apparatus

When working with chemical reactions it may be necessary to test the purity of the components you’re using. This is especially true with hobby chemists as they often acquire their raw materials from the hardware store, garden center, or pool supply. [Ken] figured out how to get around the $500 price tag of a commercial unit by building this DIY melting point test apparatus.

In this image he’s using a thermocouple to monitor the temperature of the melting surface, but mentions that you can do this with an inexpensive dial thermometer and will still have great results. That melting surface is the hexagonal head of a bolt which he drilled out to provide a concave surface for the test compound. Inside the PVC pipe is the heating element from a 40W hot glue gun. He wrapped it in fiberglass fabric which is sold in the plumbing supply to protect the area around pipe joints during soldering. The rotary light dimmer feeds the electricity to the element, allowing for adjustments to the ramping speed.

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