96. Paul Conneally

“Paul Conneally” 3: Electronics

The electronics comprise an Arduino nano as the micro-controller and a circuit board containing five surface-mount MOSFETs, used to switch the LEDs in response to the Arduino outputs.

IMGP4243The MOSFETs are designed to be surface mounted. In other words, they are very tiny and designed to be soldered by applying liquid solder to all the pins and then heating the whole thing up using hot air (or some other bulk soldering method). In the previous two projects I used a hot air rework station to do this. This is a video of my first attempt for the Candles project. I used stripboard. This is a really bad idea!

Even though I have since used plain copper-coated PCBs with insulated ares cut into them using a router bit on my Dremmel, find it very difficult to solder surface-mount components well. For this project I used the hot-air rework station to solder the five MOSFETs. Two of them did not solder properly and had to be fixed manually, using a soldering iron. In doing this, one of the transistors was overheated and damaged (zero volts on the gate no longer turned the transistor off completely) and had to be replaced. I am coming to the conclusion that, for five components, it would be easier to just solder them manually using a soldering iron in the first place. However, I intend to continue using the hot-air system as I want to acquire the skill of using it successfully.

This is the circuit board I created. In addition to the five transistors, there is a surface-mounted 5 volt zener diode (in the picture at the bottom) used to make sure the voltage test doesn’t damage the analogue input if an overly-high power supply is connected. The middle picture is with the solder paste and components prior to heating.

I soldered directly to the Arduino nano, rather than using headers. It’s attached to the frame using two grommets – held in the indent of the grommets, so away from the frame. Whereas the transistor circuit board is screwed directly to the metal strip/frame – the grommets are just acting as washers (one is not present in the image). The blue shrink-wrap contains the resistors that limit current to the MOSFETs. Note also the power supply socket in the corner (there’s a hole in the frame for the plug).



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