Android-based Reflow Brings Solder Profiles to Your Lab

[Andy Brown] is a prolific hacker and ends up building a lot of hardware. About a year back, he built a reflow oven controller. The board he designed used a large number of surface mount parts. This made it seem like a chicken or egg first problem. So he designed a new, easy to build, Android based reflow controller. The new version uses just one, easy to solder surface mount part. By putting in a cheap bluetooth module on the controller, he was able to write an app which could control the oven using any bluetooth enabled Android phone or tablet.

The single PCB is divided into the high voltage, mains powered section separated from the low power control electronics with cutout slots to take care of creepage issues. A BTA312-600B triac is used to switch the oven (load) on and off. The triac is controlled by a MOC3020M optically isolated triac driver, which in turn is driven by a micro controller via a transistor. The beefy 12Amp T0220 package triac is expected to get hot when switching the 1300W load, and [Andy] works through the math to show how he arrived at the heat sink selection. To ensure safety, he uses an isolated, fully encased step down transformer to provide power to the low voltage, control section. One of his requirements was to detect the zero cross over of the mains waveform. Using this signal allows him to turn on the triac for specific angle which can be varied by the micro controller depending on how much current the load requires. The rectified, but unfiltered ac signal is fed to the base of a transistor, which switches every time its base-emitter voltage threshold is reached.

For temperature measurement, [Andy] was using a type-k thermocouple and a Maxim MAX31855 thermocouple to digital converter. This part caused him quite some grief due to a bad production batch, and he found that out via the eevblog forum – eventually sorted out by ordering a replacement. Bluetooth functions are handled by the popular, and cheap, HC-06 module, which allows easy, automatic pairing. He prototyped the code on an ATmega328P, and then transferred it to an ATmega8 after optimising and whittling it down to under 7.5kb using the gcc optimiser. In order to make the board stand-alone, he also added a header for a cheap, Nokia 5110 display and a rotary encoder selector with switch. This allows local control without requiring an Android device.

Gerbers (zip file) for the board are available from his blog, and the ATmega code and Android app from his Github repo. The BoM list on his blog makes it easy to order out all the parts. In the hour long video after the break, [Andy] walks you through solder tip selection, tips for soldering SMD parts, the whole assembly process for the board and a demo. He then wraps it up by connecting the board to his oven, and showing it in action. He still needs to polish his PID tuning and algorithm, so add in your tips in the comments below.

Continue reading “Android-based Reflow Brings Solder Profiles to Your Lab”

Controlling a Hot Plate’s Temperature for the Lab

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.

Bang-banging your way to a perfect cake

bang-bang-oven-control

[Rob Spanton’s] house is equipped with a rather cheap oven, which was discovered while his roommate tried using it to bake part of a wedding cake. If someone took a shower during the baking process, a large portion of unit’s gas pressure was diverted to the boiler, causing the oven to shut off completely. This is obviously not a good situation for baking cakes, so the housemates decided to construct a makeshift controller to keep temperatures in line.

They started by installing a pulley on the oven’s knob, which is connected to a small motor via a long rubber belt. The other end of the belt connects to a small motor, which is controlled by a Pololu 18v7 motor controller. A K-type thermocouple monitors the oven’s temp, feeding the data through a MAX6675 converter to (presumably) [Rob’s] computer.

Since they were in a bit of a time crunch, [Rob] and his roommate [Johannes] decided the best way to keep the oven at a steady temperature was via bang-bang control. While you might imagine that cranking the gas knob between its minimum and maximum settings repeatedly wouldn’t be the ideal way to go about things, their solution worked pretty well. The cake came out perfectly, and the maximum temperature swing throughout the entire baking process was only 11.5°C – which is pretty reasonable considering the setup.

Solder station hack adds temperature control

Take that cheap fire stick you call a soldering iron and turn it into a real tool. [Giorgos Lazaridis] turned his 30 watt soldering iron into a temperature controlled soldering station by adding a thermistor just above the tip to monitor how hot things are getting. A MAX6675 takes care of the thermocouple and shoots a digital temperature value off to the PIC 16F88 which controls the unit by taking user input from a potentiometer and displaying the settings on an HD44780 character display. His use of a dissected ‘wall wort’ inside of the ATX power supply carcass used as the case for the station is a clever hack. See it melt some metal in the clip after the break.

This makes a nice upgrade to our solder station guide, which had a temperature controlled iron but lacked the sensor and automation seen here. Continue reading “Solder station hack adds temperature control”