Lighting and torches have always been a problem in survival kits. Should they be included?
Yes, they should, but only if you can find a suitable torch that is small, light, bright, convenient
and long lasting. Until the improvements of LED lighting, it has always been a compromise
and many people have made do with the Maglite range of torches such as the Solitaire and
Mini, both excellent torches but often lacking brightness and long lasting light output. LED
technology has addressed these problems to some extent and even Maglite has LED
torches in their range.
A number of years ago, an ideal contender for the perfect survival kit torch was launched, the
Pak-Lite. A very small LED unit built around a 9 volt battery snap connector. A very simple
idea, addressing all the needs ideal for a torch within a survival kit. It’s small, around 10 mm
longer than a 9 volt battery. Light weight, by only being slightly heavier than a 9 volt battery. It’
s bright and long lasting thanks to the higher power output of a 9 volt battery, which all add up
to being convenient.
How did this little wonder package come about? Well, Ben Henry, aged 15 years old,
invented the Pak-Lite for his brother, Barclay Henry, who needed a small light torch to take on
his 2600 mile walk of the Pacific Crest Trail from
success and survived the whole trail without even a battery change. This torch developed into
what is now known as the Pak-Lite Basic, a small glow in the dark snap on cap containing
two LEDs, electronics and switch unit.
Adopting, and maybe improving on the idea of the PAK-LITE, a small flashlight which attaches atop a 9-volt battery, we proudly present the HAK-LITE.
An important consideration is the choice of LEDs. The sample here uses two 10mm (T3-sized) white LEDs from www.ebay.com . With a tight beam of 6 degrees, it casts a very useful light with only 20mA draw.
A most useful improvement over the original light is replacing the switch with a simple Touch-control. This allows the circuit to be completely sealed, with 2 small metal touch plates at opposite ends acting as the switch itself.
Performance is very good; average draw is around 12mA to drive both LEDs to 20mA, which translates to over 90% efficiency and an alkaline battery will run the light brightly for 30 hours. The light will continue to run at diminished brightness until the battery is below 6-volts. This means the light will work with earlier rechargeable batteries with only 7.2-volt output. For slightly less light, but double the run-time, change R2 to 180Kohm.
When the coil saturates, the transistor switches off, and the coil discharges through diode D1 and the LEDs. The cycle then repeats itself.
The 5uF capacitor smooths out the charge/discharge pulses to provide a steady current to the LEDs.
Q1, a general purpose PNP transistor (2N3906, 2N4403, BC327 etc), can be used for the touch-control. Shorting or touching the end of R1 to ground will allow a small current to flow to Q2 to activate the circuit.
You can use any diode for D1 rated for more than 250mA and 20-volts. Any hi-gain NPN transistor designed for disposible flash camera use will work for Q2, as will a BC337, but with lowered efficiency.
