OK, my labelling could be improved! :)
I had recently replaced the LCD screen in my laptop and had dismantled the old, cracked one. There was a nice strip light of tiny surface mount white LEDs along the top of the old display that was used for backlighting. I decided to desolder them and use them for this project.
My previous microscope came with an incandescant bulb which required mains. The bulb ran hot and evaporated my subjects. The microscope was also tethered to the nearest power point. I decided to try batteries for this project as I found having to use mains was inconvenient. LEDs run cool and are power efficient. An advantage is that the LEDs project a directional light which suits this suits our purposes. The LEDs also have a more pure white light compared with incandescant bulbs. Being able to use the microscope anywhere, including out in the field if required, is not a bad thing either.
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OK, my labelling could be improved! :) |
 Wiring inside base: 500Ω pot, SPST switch, 9v clip & battery. Connector to PCB dangling... |
 Magnified view of PCB. Messy but it's hard working with tiny recycled SMD LED's. The footprint of the LEDs was designed to cover all but the widest magnifications. Note also that the LEDs have a very directional emmission which helps for this use. The yellow of the LEDs is just part of the colour correction of the LEDs. There is a 120Ω resistor in series and there are 17 LEDs wired in parallel. |
 The PCB epoxied to the (created) baseboard. I added a ring of tin foil to possibly increase illumination and to minimise any colour cast reflected from the light blue ABS plastic that the baseboard is constructed from. |
 Baseboard attached to the microscope base. The connector is polarised to prevent erroneous connection. The reflective foil is kept well clear of the PCB to prevent a short-circuit. |
 Switched on. Again, the LEDs are directional so most of the light goes where we want it, up. |
 A circle of frosted plastic, which was also pulled from the dismantled LCD display, was cut out and inserted below the clear glass plate. The LEDs project their light up through this. |
 The completed underlight. |