Monthly Archives: January 2017

Reflow Oven Control with a Raspberry Pi

ntroduction of SMT or Surface Mount Technology components have made it more difficult for Do-It-Yourself enthusiasts to solder these components using a soldering iron. The switch from through-hole components to SMT types had actually made hand soldering easier initially. However, with the introduction of BGA and similar packages that require blind soldering and extremely small packages that are difficult to handle manually, hand soldering with a soldering iron is now practically impossible.

Such special packages need a reflow soldering process to solder them properly to the PCB. This is easy to make with a single board computer such as the Raspberry Pi or RBPi, and a convectional hot air oven designated originally for a bakery or gastronomy purposes. The RBPi helps to make it an open-source universal reflow oven that is also web enabled and PID controlled. Another advantage of using the RBPi as a controller for this oven is it can be used also as a sophisticated pizza oven. Unfortunately, the two functions are not interchangeable, meaning you must not heat food in an oven that you have once used for reflow soldering purposes.

Apart from the RBPi, you will also need SPI-driven cold-junction thermocouple converters, for which, you can use the MAX31855 or the MAX6675, useful for K-Type thermocouples. The above ICs offer cold-junction compensation and digitize the signal from K-Type thermocouples. The data will be in a signed 12/14-bit, SPI compatible, read-only format.

You will also need Solid State Relays for the heaters and the fan, and if these are of the GPIO driven types, intermediate drivers will not be necessary for the RBPi. The heaters are best made of PWM driven MOSFETs, preferably operating at 12 VDC.

The control software runs as a Python daemon on the RBPi. An OS independent multi-user web-client offers live monitoring and remote control. The profile/curve management and slope calculator is browser-based. The software developed for demonstration is a fully functional PID controller, while incorporating a simulator.

The demonstrators have used an EKA KF412 professional hot air oven produced by Teknoeca srl from Italy. The oven uses hot air temperature transfer (convection) as against infrared, and this was considered preferable. The power consumed by the oven was 2.6 KW at 230 V, producing a maximum temperature of 300°C.

The oven chamber has adequate insulation and this increases its thermal inertia. Therefore, once the oven crosses the maximum reflow temperature, a natural cooling process does not offer quick but controlled cooldown. This is necessary to return the solder paste to its rigid state.

A radial fan mounted on the back of the oven handled the above situation. The RBPi drives this fan via a GPIO pin, and it blows fresh cold air at room temperature into the oven. This gives the RBPi total control over the heating and cooling rates of the oven, and it is possible to define a proper reflow solder profile. It is important to know that the reflow profiles for lead-free solder are different from the profile required by leaded solder.

New Velocity & RBPi: Charting an undiscovered island

Not many engineers are familiar with cartography, the map-making process. However, with advances in technology, map-making also uses computers, including using them for gathering, evaluation, and processing the source data. Furthermore, cartographers use the computer for intellectual and graphical design of the map, down to the drawing and reproduction of the final document.

There is more to cartography than mere map-making. Being an academic discipline in its own right, there exist professional associations – regional, national, and international – educational programs, conferences, journals, and other identities related exclusively to cartography. Although technological change has always affected the way cartographers prepare their maps, the computer helps them gain unparalleled control over the mapping process.

New Velocity, a machine based on the single board computer, the Raspberry Pi or RBPi, helps in the charting process. Luiz Zanotello created New Velocity at the University of the Arts at Bremen. This project has been especially helpful in investigating a certain charting error as yet persisting in cartographic maps. It involves the entanglement of physical phenomenon and data, to both of which the digital media gives the same weight.

This anomaly existed for over a century in the form of Sandy Island, located near the French territory of New Caledonia. Although the island appeared on several maps from as early as the late 19th century, an Australian surveyor ship, passing through the area, discovered that the island actually did not exist, and never had. This was followed up by removing the map from all maps. Luiz has reproduced the conditions upon which the island was seen in 1876. This project recreates the charting glitch that put the non-existing island in maps worldwide. By manipulating the digital presence, New Velocity generates a new dataset to support the existence of this fictitious island.

New Velocity has a platform to replicate the up/down movement of a ship floating over high seas. On the platform is an infrared proximity sensor for scanning sand piles. The RBPi maps the spacial data from the proximity sensor for visualization in real time. New Velocity has four preset modes, one for each dataset it records. For instance, it records coastline coordinates, digital geo-tagging, topographical elevation, and water depth surroundings.

New Velocity generates evidence of the presence of an islet in each set of datasets within the range of the island. It also uploads the data posteriorly to the open data bank of Sandy Island for spreading.

The project uses an RBPi2 running the Raspbian Jessie and openFrameworks for generating outputs that include visuals and mapping. Two NEMA 17 stepper motors help to achieve the physical motion. An Arduino Uno running the AccelStepper Library software program operates the motors via two DRV8834 Low-Voltage Stepper Motor Driver Carriers. For sensing the sand pile, New Velocity uses the GP2Y0A41sk0F Analog Distance Sensor, made by Sharp and it can measure from four to 30 cm. The entire project is encased in handcrafted wood and acrylic cases with red LEDs and a toggle button.

New Velocity proves that effective mapping is crucial for finding solutions to cartography, many of them being environmental. Without accurate maps, several activities related to the earth’s surface, such as mineral prospecting, forest management, locational analysis, road construction, weather prospecting, and so many more would remain unpractical.