Showing posts with label build. Show all posts
Showing posts with label build. Show all posts
Sunday, November 9, 2014
Build LED Light Pen Schematic
Physicians and repair engineers often use small light pens for visual examination purposes. Rugged and expensive as these pens may be, their weak point is the bulb, which is a ‘serviceable’ part. In practice, that nearly always equates to ‘expensive’ and / or ‘impossible to find’ when you need one.
LEDs have a much longer life than bulbs and the latest ultra bright white ones also offer higher energy-to-light conversion efficiency. On the down side, LEDs require a small electronic helper circuit called ‘constant-current source’ to get the most out of them.
LED Light Pen Circuit Diagram
Here, T1 and R1 switch on the LED. R2 acts as a current sensor with T2 shunting off (most of) T1’s base bias current when the voltage developed across R2 exceeds about 0.65 V. The constant current through the white LED is calculated from
R2 = 0.65 / ILED
With some skill the complete circuit can be built such that its size is equal to an AA battery. The four button cells take the place of the other AA battery that used to be inside the light pen.
LEDs have a much longer life than bulbs and the latest ultra bright white ones also offer higher energy-to-light conversion efficiency. On the down side, LEDs require a small electronic helper circuit called ‘constant-current source’ to get the most out of them.
LED Light Pen Circuit Diagram
Here, T1 and R1 switch on the LED. R2 acts as a current sensor with T2 shunting off (most of) T1’s base bias current when the voltage developed across R2 exceeds about 0.65 V. The constant current through the white LED is calculated from
R2 = 0.65 / ILED
With some skill the complete circuit can be built such that its size is equal to an AA battery. The four button cells take the place of the other AA battery that used to be inside the light pen.
Wednesday, September 24, 2014
Build a Metal Detectors CCO schematic Diagram
This is a schematic of a simple metal detector that uses technology CCO, by Coil Coupled Operation. Thomas Scarborough designed this new incarnation of the metal detector, a new genre that he invented in 2004. This is the first project of the Internet and can be built easily.
Metal Detectors CCO Schematic Diagram
Thursday, April 4, 2013
Wiring Dual Coil Build Trinituner
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