This was one of those projects that should have taken an afternoon and didn't, however it's now complete and working rather nicely.

I already had a box from a defunct project that had the 4x20 LCD display installed and power switch, mains transformer and a mains IEC socket on the rear so I decided to re-task it for this.

Inside is a PIC18F25K22 running this show, and the device can monitor up to three channels. Each channel has a 5-pin din connector and cable that connects to a Maxim DS18B20 temperature sensor.
You can set the alarm temperature independently on each channel, and the project starts beeping and flashing the LCD backlight if a maximum is exceeded. I also included a relay that can be used as a power interrupter for the project under test. This way I can leave a project on soak but if it starts to over heat, the power can be cut automatically.

The reason it took longer than anticipated was for some reason the PCB never etched correctly and I had some messing around to do. The software only took around an hour to write and debug. I love Proton BASIC.

...and the reason it's three channels and not more, well I happened to have three 5-pin din sockets in my junk box. If I'd had more... who knows.

If anybody is interested I'll make available the circuit diagram, PCB foil and PIC firmware but this really is an easy project to design and build.

So, now that's up and running, I can get back to the original task of designing a decent voltage boost converter.

The organisation I work for have many buildings and most contain at least one computer or equipment room. In one particular building, the computer room air-conditioning is temperamental to say the least and because people don’t often need to go in there, one more than one occasion the air-conditioner has tripped and it’s been a while before anybody’s noticed the tropical heat wave going on in there.

Yesterday I designed and built a temperature alarm system. It’s nothing too clever, just three large LED displays in a box, with an 18F25K22 PIC running everything. A Dallas 18B20 sensor has been mounted in a small box and is connected via a piece of three-core cable to the main display unit that can be mounted outside the room.

You can set the maximum allowed temperature and this is stored in the PIC’s EEPROM.

If the temperature rises about the pre-set maximum, the display flashes and there are a couple of 5v buzzers inside the main unit to help attract attention.  There are three additional indicator LEDs housed within the main display unit as well. One is a green LED that flashes indicating all is well, a yellow LED that indicates that the unit is in setup-mode (started by powering on the unit whilst depressing the external push-button switch mounted on the side), and a red LED that indicates the temperature alarm has been tripped at some point. Depressing the push-button switch once clears this indicator and the complete unit is powered from a small 9v plug-in mains transformer.

Inside the unit there are two PCBs. One is the top display board, and the other is the logic and PSU board.

If people are interested I’ll publish the design details for this unit.