LED Testing Tool       Code: RK-LEDTool

Modern Light Emitting Diodes (LEDs) have revolutionised the way hobbyists can light model railway vehicles and buildings. LEDs are available in almost every colour imaginable, from brilliant white to stunning purple, and in a range of sizes that enables the modeller to represent close to the correct dimensions for many applications.

It is essentail that LEDs are always used in conjunction with a ballast resistor. If connected directly to a power supply, the likelihood is that the LED will light brilliantly for a very short (and final) time.

This handy unit (shown above) comes in a little battery powered box. It can be used to determine a number of things. The LED to be tested is connected to the box by sliding its leads into the miniature rivet like terminals. The tool firstly acts as a go/no-go tester did that LED survive being tried out directly across the battery terminals? It is also very useful when the leads have been cut off and one doesn't know which is positive and which is negative a quick connection to the box both ways soon shows which lead is which. The tester has a number of test points which enable the LED to be tested at currents from 0.5 milliamp (mA) to 20mA. (Normally, LEDs should not be run at greater than 20mA for maximum life.) This facility allows the modeller to see how bright a LED looks at various currents, and hence to decide at what current one wishes to operate it.

The Tool indicates the current, and the associated value of ballast resistor at 12 volts. Two sets of terminals are provided at 10mA, to allow comparison of different LEDs at the same current. To calculate the resistor required if one is using a different supply voltage, one can apply Ohm's Law, or use the handy resistor chart (RK-RESCHART) available separately, which shows the ballast resistor values needed for supplies of 5,6,9,12, and 15 volts at various currents. This chart also shows the colour code for these resistors in both 3 band and 4 band variations. The reverse of this chart shows the real world size of various common LED sizes in different modelling scales, and also provides a scale ruler for O/48, HO/87, N/160, and Z/220 modellers.



The diagrams above show the unit, and the correct way to connect a LED through a ballast resistor.


Ready to use price for             RK-LEDTool: $22-50
RK-RESCHART: $4-00




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All kits available from :
Aztronics Pty Ltd       Phone 8212 6212
170 Sturt St,                     Fax 8212 4212
Adelaide, SA, 5000.                                
email:               sales@aztronics.com.au

Information:         David Crosby         david@railwaykits.net

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Last updated 5th February, 2017.
(C) D. Crosby, August, 2010.