The module Keyes_SR1y is the KY-019 5V relay module for Arduino (or most anything else really, it’s not as if it plugs straight into the board – you’ve got to connect the pins off to disparate parts of the Arduino board). Relays mostly are used to switch larger loads than opto-isolated switches; they’re generally used in cars or for switching household devices on and off. Large currents are dangerous; you have been warned. This module can switch 250V at 10 amp – at least, that’s what the printing on the box says. The 5 volt part is about the voltage needed to switch the relay. I haven’t measured the current used to switch, but it runs happily off the current supplied by a laptop USB port.

The circuit board marks the 5 volt (+) and ground (-) lines (because of the current draw, these are fed from the power circuitry of the Arduino, rather than the GPIO pins); the remaining line is a digital input; the program code or “sketch” to control it looks something like

const int relayPin=5;
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, HIGH);

assuming you’ve hooked the relay up to pin 5. Split the code into the body, setup(), loop() and elsewhere as appropriate.

HIGH energizes the relay (switches it from its normal state), LOW does the opposite (and switches it into its normal state). When it changes state it makes an audible click. On board the module is a red LED that lights up when the relay is energized. The relay has Normally Open (NO) and Normally Closed (NC) circuits, so save some power and use the appropriate one for the normal state, or design for a useful fail-safe state.

This module is one that you’ll find in the various Arduino Module Packs around the place.  One guy has made an attempt to identify and document the lot: http://space.makehackvoid.com/wiki/DxArduinoModulePack

Making stuff is fun. But sometimes you need a 3D printer, and Bunnings are out of them – besides, they're thousands of bucks. What to do?

There's a place in the USA called TechShop which is a workshop fully fitted out with most imaginable tools, industrial grade. I lust after it. $30 for a day-pass, $100 for a month. Only problem is

, cool ideas like this don't seem to get financial traction. If something like this opens up in your area, make sure they're going to hang around before you part with long-term payments.

Parallels have been drawn to the MIT FabLab, which is in a number of countries, but seems more focused on technology than materials.

Geoff has built a Homemade Air Conditioner – by running ice water (made from ice-cubes, and bottles of water he’s frozen in his freezer) through copper tubing at the back of a stand fan – fluid motion provided via capillary action.

Once the water runs out, the house has cooled off enough that the fan alone provides sufficient cooling.

That would be evaporative cooling, Geoff.

Geoff also suggests adding salt to your mix, because

this will drop the freezing point of the water and increase the cooling effect of the fan.

Uh, no. That would be lowering the freezing point of the water. It doesn’t lower the temperature of the water, it means that it takes more energy to freeze the water in the first place. But you’re already dumping frozen water into your water bucket, so you’re too late.

Geoff apparently had to “poke a little hole” through his flywire for the exhaust of his water tube, but draws the line at digging up his landlord’s garden to make a geothermal cooling system. I’m glad for his landlord, but what’s the problem with digging up a backyard only to cover it up again? A hole in your flywire is there for good!

Geoff goes on to suggest that if you hang a car radiator off your fan – in a bid to increase the efficiency of the system – you might want to check it can handle the weight.

Nice work Geoff.