Step 4 - wiring the internals + assembling
Once everything has dried, you can start wiring up the switch circuit.
The LED is rated at 1.5v, so we can use an AAA battery without any other components and it should work fine. First of all, you need to work out the polarity of your LED - which way round you need to conenct the battery. This is a little harder than you may think, as IR light is not visible to the naked eye. Most digital cameras, however, can detect the light. We used the camera on our Nokia n95 to view the LED whilst touching the wires onto the battery. It should be clear which way round you need to wire the battery up.
Once this is determined, the next step is to wire the switch, the LED and the battery in series so that, when the switch is pushed the IR LED is powered. Remember that the wires need to move up and down with the switch, so allow for this movement by leaving plenty of excess wire. We bent the wire round so that it would move freely inside the vitamin tube - see picture 2 in the gallery.
Initially, we used a battery holder from Maplin’s - but the connections did not work leading to a faulty circuit. Instead, we soldered directly onto the battery. This is not recommended - applying too much heat to the battery may damage its internals and cause it to malfunction or even explode. We have since found battery holders from another distributor that work well. Again - do not solder directly onto the battery. Use a battery holder to ensure safe construction of your FriiSpray can.
Once you have connected the battery and completed the circuit, test it again to make sure that all is well and the IR LED lights up when then switch is depressed. Then tape up the bare soldering with insulation tape. Next, you may need to modify the switch to fit into the can/tube assembly - we cut the corners off as you can just about make out in picture 3.
When inserting the internals, be careful to position so that there is enough clearance for the button to be depressed fully. Once you find a suitable position, glue the sides of the switch assembly to the tube. Be careful not to get any glue inside the switch that would cause it to seize up.
To ensure that the switch assembly stuck in the correct place, we used a small screwdriver to support it until the glue was dry.
Once you are happy that the glue is fully set [leave it for plenty of time] - you should have a completed IR spray can.
Pat yourself on the back, and go test it out.
Please Please be very careful. I was shocked to see a pressurized can being punctured in this way. Many years ago, a colleague lost a foot when a can he kicked exploded. If the valve is blocked (as often happens in old paint cans), you may think the can is empty when you press the valve. Puncturing any pressurized vessel is a very dangerouse thing to do. You are playing with a potential bomb. Also batteries if heated are VERY liable to explosion. So please be warned.
Warmest wishes
Alan
Alan - thank you for your advice and warnings. We had changed our ways of constructing cans but had not updated the instructions accordingly - which we now have done. We only work with recently used low pressure cans designed for graffiti-art but are aware of the dangers. To re-iterate: we do not condone or encourage the de-pressurisation of aerosol cans as shown in our tutorials. Please use an old washing-up liquid bottle or a similar vessel that is not pressurised. We are currently designing some custom 3D-printed cans that will be available soon.
We have also found that battery holders from another distributor to be of good quality and much more suitable than soldering directly onto batteries. Please do not solder directly onto batteries as this is potentially very dangerous - instead use an appropriate battery holder, inserting the battery after you have soldered on your connections.