I’ve also realised that whilst there are many web sites containing lots of projects to build, they tend to supply you just a circuit diagram and if you’re lucky, a .HEX files for the CPU. These are ok for seasoned constructors who in reality, probably just want to grab some circuit ideas and wouldn’t usually build the project in it’s entirety in the first place, but for beginners and novices, something more akin to what the great electronics magazines of yester-year used to produce is more appropriate and that’s why I’ve opted to try and provide full construction details for some of my projects.
So, with all this in mind, I’m currently working on another project – an Evaporator.
Ok, actually this is a device that produces a small amount of heat and has a thermometer and timer built in. You set the run time in minutes, maximum temperature you want, and the device attempts to maintain a “hot-zone” at the required temperature for the specified time. In this version of the project, I’m using a 12v / 20w halogen lamp has the heat source and it’s used to gently warm an evaporating basin (small porcelain dish) that’s full of liquid that in turn has a solid dissolved in it. You could use it to recover the salt (and the other solid material) from a few mL of sea-water for example. With a few changes to the physical hardware layout and perhaps a different heating element, you could use this as an incubator. The unit has an LCD display, some push button switches, a temperature sensor, a MOSFET that can switch around 35A if required, PSU section, and a PIC 18F25K22 running some firmware written using the AMICUS18 free compiler; this means you can customise the firmware as you please. One upgrade may be to fit a fan so that if it gets too warm it can cool; perhaps the addition of a Peltier module - the skys the limit when you start thinking about the possible options.
The prototype which is sat on a bread-board right now, works remarkably well. I use PWM (Pulse Width Modulation) to drive the heater (lamp) via the MOSFET. The heat from the lamp is detected by a DS18b20 1-wire temperature sensor (I had a couple spare from my digital thermometer project), and fed back to the PIC. The PIC constantly monitors the temperature and using a very simple algorithm attempts to maintain the temperature by adjusting the brightness of the lamp. Once it warmed up, it was maintaining the temperature to within 0.1 oC which for a first attempt was rather impressive I thought.
I’ll publish full construction details soon, probably when I get back from vacation.