LED Torch

flashlight goes high-tech

You would be forgiven for thinking that a torch is probably the ultimate minimalist circuit: all you need is a battery, switch and bulb and you’re in business but add a microcontroller and you can build in some interesting features that make the humble torch rather more useful…If you made a wish-list for the ideal torch it would probably start with the need for it to be small enough to fit comfortably in your pocket or rucksack but at the same time be powerful enough to provide enough light at a couple of metres distance to work by for many hours. The environmentally aware would also vote for a rechargeable power source that would hold its charge even if the torch had been lying in a drawer, unused for a couple of years.

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Materials

012019-PCB.pdf

012019-11.zip

Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

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PCB

Download Gerber file: 012019-1.zip

Component list

Resistor:
R1 = 680 ?, SMD size 0805
Capacitors:
C1 = 220nF ceramic, SMD size 0805
C2 = 33µF 20V, SMD size 2220
C3 = 1µF 6.3V, SMD size 1210
Inductor:
L1 = 233µH (100kHz), ESR = 0.27 ?
Pot core P9.0x5.0/N26 (Al = 250) with 30.5 turns of 0.22mm dia. ECW
Semiconductors:
D1= BAT48 or 1N4148
D2-D8 = LED, 5mm, white, 6400mCd (Nichia, NSPW500BS) (www.nichia.co.jp/lamp-e.htm), available from Conrad Electronics
T1=BSP308, BSP319 (RON=50m?)
T2=BS170, BSS138 (RON=5?)
IC1=PIC12C672 04/SM, programmed, order code 012019-41
IC2=LM9140-2.5 or TL431
Miscellaneous:
S1,S2 = SMD switch, 1 contact (Mentor 1254.1007 or 1301.9314 or Omron B3FS-1052 from Farnell)
Battery = Sanyo UR18650 Li-Ion, 1350 mAh (18mm, length = 65mm, weight 40g) or Sanyo UR18500 Li-Ion, 1100 mAh (18mm, l = 50mm)