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- Black framed mirror – the frame must be able to accommodate the lamp holders and be of a suitable material to screw in to. (I used a frame with external dimensions 840mm x 640mm, and a border width of 80mm.)
- Laser cut logo on plywood (I used an online service).
- Appropriate power supply (see Step 1).
- 14 off brass lamp holders, such as RS Stock No. .
- 14 off 24V 25W clear incandescent light bulbs (NOTE – not “normal” domestic 240V bulbs).
- Brass wood screws – ½ inch x No8 roundhead.
- Black spray paint.
- Spray adhesive.
- Wires – use an appropriate gauge wire for your bulbs and power supply.
- Commoning blocks, such as RS Stock No.
(NOTE – This part is not required if you are going to individually control the bulbs, as described in my Lighten the Load project).
The total cost of this project (excluding the power supply and the control electronics as described in a separate blog post) was about £300.
Step 1 – Power supply choice
It is important to use a correctly rated power supply. This should be current limited or fused.
If you are using different voltage or wattage or number of bulbs, please do your own calculations.
For 14 off 24V 25W bulbs:
The maximum current draw per bulb is
P/V = I
25/24 = 1.04 Amps per bulb
There are 14 bulbs, so if all were on simultaneously at the maximum voltage, that would be a current draw of
14*1.04 = 14.56 Amps.
To run all the lamps at full brightness, the power supply would have to be able to provide this. And, of course, 24 Volts.
Lightbulbs are non-ohmic conductors – they do not follow Ohm’s law. The resistance across the filament increases when the temperature of the filament increases, and so the current through it is not directly proportional to the voltage across it. Therefore, halving the voltage will not halve the current.
Although I only intend to use a maximum of 12 Volts for each bulb, I still used a power supply that is rated to cover the 14.56 Amps maximum that I could potentially draw.
Step 2 – Logo
- Make the logo. This could be a positive or the negative (stencil) – depending on the logo and how much of the mirror you want to see. I used a laser-cut stencil of the “Makertorium” logo. I sent the svg file to an online service. Tip: Make sure the logo will fit inside the mirror frame.
- If the logo does not fit, mask off and spray matt black paint on to the areas of mirror you do not want to show. For me, the plywood stencil was too long for the mirror frame, so I had to cut it to fit. It also was only 380mm wide, whereas the mirror was 480 mm wide. I masked off the top and bottom of the mirror and spray painted it so the plywood and logo stood out.
- Using spray adhesive on the back of the stencil, attach the logo to the mirror. Tip: Do not push too hard or you may crack the mirror (yes, I did that).
Step 3 – Mark out and drill holes for lamp holders
- Space the lamp holders equally around the frame – or until they look good – this will depend on the actual dimensions of your frame. I used a total of 14 lamp holders.
- Measure the distance between the centres of the holders, and mark the centres on the back of the frame.
- Drill holes in the centres large enough to thread two wires through.
- Mark the screw holes for the lamp holders on the back, and drill a pilot hole through the frame.
Step 4 – Attach lamp holders
- Pull two wires through each hole: Tip – tape the two wires together – so you can easily see which pair go together.
- There will be 28 wires in total – use cable clips to keep them as tidy as possible. I put my wires around the edge of the frame. They could all go to the centre. Leave a loop so you can wire the lamp holders.
- Wire the lamp holders – it took me a while to remember that unlike LEDs, incandescent DC bulbs just need a positive and negative, it doesn’t matter which way round you wire them!
- Attach the lamp holders using brass round head screws.
- Add the bulbs.
Step 5 – Wire up
NOTE – only complete step 5 if you want all the bulbs to light together. If individually controlling them, miss this step and go to my Lighten the Load project.
- Check that you have thick enough wires from the power supply, and the power supply is sufficiently rated to light all the bulbs – refer to Step 1.
- Using a communing block, connect one wire from each bulb together.
- Using another communing block, connect the other wire from each bulb together.
- Connect the positive from the power supply to one block, and the negative to another.