Got given some interior automotive festoon LEDs by a friend who brought the wrong fitting for his car. What better use but to make a random but useful gift for your girlfriend?
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Step 1: Procure Parts
Dressing Table Mirror - Argos - £16.99
9V Lithium Battery - Amazon - £7.62
Switched PP3 Battery Holder - Maplin - £2.49
ABS Project Box - Maplin - £5.69
9V to 12V Boost Converter PCB - Makertronics - £7.04
12V Festoon LEDs - eBay - £3.99
LED Brackets - RS Components - £4.02
Single Core Wiring
2x Terminal Blocks
Double sided sticky tabs
Step 2: Create Commonised Terminal Blocks
Take a terminal block and commonise it at one end. To do this:
Cut 1 inch lengths of wire and strip 5mm at each. Cut n-1 lengths of wire, where n is the number of terminals in the terminal block. These will be used to form a daisy chain connection between the terminals to ensure there is continuity across the terminal block. This will be used a busbar.
Commonise another terminal block like this, this will be used to commonise all GND connections.
Step 3: Prepare the Mirror for Mounting Brackets and Terminal Blocks
Remove the mirror from the box, only the mirror - leave the wooden base and side panels in the box as these won't be needed unti later.
Use pencil and draw lines mid way through each bezel (shown in the attached diagram as red lines)
Measure the length of the mirror, divide this by 3, use 1 edge of the mirror as a datum and centre punch a hole (I used a nail and a hammer) at 1/3 of the way along the bezel and 2/3 along the way. Do this along both lengths and both widths of the bezel. These holes will be used to mount the LED brackets.
Attach the previously created terminal blocks to the to the rear of the mirror using double sided sticky.
Step 4: Screw Into the Bezel
Screw some 6mm length screws into the centre punched holes. Ensure your screws are not too long as they may come into contact with the mirror itself, or even penetrate the rear surface of the bezel.
Remove the screws, and store them for later use to mount the brackets.
Step 5: Prepare the LED Brackets
Each side of the bezel will mount 2 LEDs. So to reduce the number of connections needing to be made (and aid neatness), solder cable between the two left hand connections of two brackets, ensure the soldered wire is long enough so that the brackets can be mounted onto the previously drilled holes along the bezels.
The brackets have no polarity, it just depends on which way you install the LED and subsequently supply the power and GND.
Now solder cable between the two right hand connections of the two brackets. Use a different coloured cable to distinguish between positive and negative wiring.
This soldered connection will now be the positive supply cable for both LEDs on a bezel side, or a shared GND.
Do this for the 4 pairs of the LED brackets.
Step 6: Wire Up
Install the LEDs into the brackets. Ensure that the positive side of the LEDs are attached to the side of the brackets which you designated as the positive cabling.
The only way I found out which side of the LEDs was positive and negative was by supplying 12V and GND across a spare LED I have and making a note. Luckily the LEDs were not affected by the reverse polarity and continued to operate OK once I removed the connections.
We will now need to connect each bezel negative and positive connection to the respective terminal block. With the LED pairs attached to the We will now need to solder cable to each bezel positive and negative connection and run these cables to the positive and negative terminal blocks respectively.
Roughly run a length of wire from a positive connection on an LED pair to one of the terminal blocks. Cut this length, strip the insulation 5mm on each end, solder one end to the positive connection on the LED pair and run it neatly to one of the terminal blocks and screw the cable into the terminal block. This will now be your positive terminal block.
From the same LED pair, run the other colour cable which has been used from a GND connection point to the other terminal block. Cut this length, strip the insulation 5mm on each end, solder one end to the negative connection on the LED pair and run it neatly to one of the other terminal blocks and screw the cable into the terminal block. This will now be your negative terminal block.
Do this for all 4 LED pairs around the bezel. To aid neatness a screw can be screwed into the corner as shown in some of the images to ensure that the ran cable lengths don't overlap onto the mirror and stay around the bezel.
When all LEDs were connected up I used a computer power supply 12V and GND connection from a 4 pin Molex connector and hooked up the respective pins to the terminal blocks to test that everything worked. An ammeter showed that all 8 LEDs drew a average of 200mA.
We will now hook up the power supply.
Step 7: Create Power Box
Take the project box and use a side cutter to cut 5mm vertically at two points 10mm apart. Use a stanley knife to score along the edges of these two cuts and use a plier to remove this little section of the plastic. The resulting hole is shown in the images. This will be used to feed wires to the terminal blocks from the project box.
A DC 12V mains plug could have been used for power, but to ensure portability, a 9V battery was used. The voltage obviously needed to be stepped up so a boost converter was used (details found in step 1).
Score the stripboard using a stanley knife to form a section which will fit horizontally into the project box. Hold the stripboard at the edge of the table with the scored parts of the board just hanging over the edge and apply pressure to snap the stripboard.
Solder the boost converter PCB to the produced stripboard, so that each pin of the PCB is sitting on a different track on the board.
Solder the positive connection of the PP3 battery holder to the same track of the VIN pin on the stripboard.
Solder the negative connection of the PP3 battery holder to the same track of the GND pin on the stripboard.
Apply some blue tack lightly to the switch on the battery holder and place the battery holder onto the project box lid in the desired position and lift off, hopefully the blue tack will remain on the lid at the point where we will need to drill a hole to allow access to the switch once the battery holder is mounted. Keep trying if the bluetack does not stick!
Where the blue tack has stuck, centre punch a hole through the blue tack. Remove the blue tack and draw an X using a knife so it is easier to see. This X will need to be drilled (I used trial and error to find the size). Drill a hole and place the battery holder on the box lid and see if the switch is easily useable. If not drill a bigger hole. When happy with the hole size, apply double sided stick to the back of the battery holder.
Roughly run a length of cable from the positive terminal block to the inside of the project box. Strip insulation as normal, secure 1 side to the positive terminal block and solder the other end to the VOUT pin track on the stripboard.
Roughly run a length of cable from the negatuve terminal block to the inside of the project box. Strip insulation as normal, secure 1 side to the negative terminal block and solder the other end to the GND pin track on the stripboard.
Insert a battery into the holder, and secure the holder lid. Insert the stripboard into the project box and ensure the exterior wires are placed into the section which was cut earlier and close the project box.
We should now be ready to power up
Step 8: Voila
If everything has gone to plan (and the instructions were good enough!) you should have a working LED mirror.