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Tuesday, April 23, 2019

Drive a LED with a Constant Current

This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current via LED and NPN is limited by R. 20mA may be ok 15mA even better. Or LED blows even transistor goes.

LED Voltage Level Indicator

BC547 is like 100mA-40V-200b, Limit collector current to 60mA, use it at less than 25V and depending on the individual transistor you may get a DC current amplification of 200 times. That is 1uA of base-emitter current could give a whooping 200uA of collector-emitter current.

Constant Current Source LED Drive

Still Thinking we do not have the Lower-NPN we calculate the resistor. Vcc - ( 2 LEDs * 1.7) - Vce = Vr that is the voltage across the resistor. You know ohms law and the current needs to be 15mA for a bright and long lasting LED. Lastly 1.7 the forward drop of a green LED and 0.6 a saturated or Turrned-On NPN Vce.

Mains Voltage Current LED Indicators

Now you use the Lower-NPN, The above calculations do not hold anymore. Let us think a small current is flowing in the LED. Then the voltage across R is less than 0.7V, that means base-emitter diode of the Lower-NPN will not get to conduct. The Collector does not draw any current away. Now think that more current flows in LED, the voltage across R builds up above 0.7V the Lower-NPN is biased. The collector of Lower-NPN starts drinking current from the base of the Upper-NPN. So The Upper-NPN starts losing its bias. This lowers the LED current and contains, regulates or controls the LED current as shown in the formula.
    More at - Schematics of delabs: LED-Circuits

    Monday, April 08, 2019

    High Speed Photography - HSP

    Here is a small list of photography related circuit and projects including High Speed Photography or HSP that uses Electronic Circuits to operate the Trigger or Lens Shutter.

    High Speed Photography

    "Many physical processes evolve on timescales shorter than the human eye can resolve. Effectively, this means the details of how the process changes with time are lost in a blur. High speed photography, or HSP, is simply photography with extremely short exposure times,....

    High Speed Photography - HSP

    ....All control systems can be classified into one of two broad types - Open Loop and Closed Loop. The difference between them is the use of feedback via input signal. For the DIY high speed photographer, the difference equates to reliability, expense and simple electronics. "

    Lightning Activated Camera Shutter Trigger

    This circuit is used to trigger a camera's electronic shutter circuit when a flash of lightning is present. This circuit would also work for photographing fireworks displays or other events involving flashes of light.

    Darkroom Camera Shutter Timer

    This circuit was designed to control a film exposure shutter for a darkroom. It has 8 time steps ranging from 0.35 seconds to 4 seconds

    Motorized Video Camera Mount

    This article describes a motorized, waterproof mount for a miniature video camera. If a suitable waterproof camera is used, this unit can be used outdoors.

    Monday, April 01, 2019

    LED Lamps and Flashlight

    Colorful Light Emitting Diodes and LED Lamps. Colorful Lights, LED Lighting, Automobile Lamps, Cycle Lights. Decorative LED Effects. Annunciations and Indicators. LEDs are Omnipresent.

    LED Hobby DIY Circuits

    Series Connected Voltage Boost Circuit

    ....Eventually a topology emerged that can actual run a 3.5 volt LED when it and the driver in series with a 1.5 volt flashlight cell. Well kind of, anyway. The trick was to put one additional component, a diode that is actually part of the driver, in parallel with the LED. Read on.

    LED Torch Project

    I looked around for an integrated LED boost driver with an input voltage of less than 4.5v and current limiting up to 1A but there appears not to be any! None that I could order from Farnell anyway. The CAT4139 and CAT4240 come close with a current handling of 750mA but Farnell do not stock them.

    Solar Charged LED Utility Light

    The LED array can provide enough light to illuminate a small work area or reading area at night. The red, orange, yellow and green LEDs broaden the lamp's color spectrum to produce a slighly warmer color temperature.

    LED - Brooke Clarke

    If the light source was another identical candle then it would be the same distance from the paper. But if a reflector was on the light source candle it could be moved further away. The light output from the T series LEDs is specified in milli candelas. A bright white LED running at 20 ma might be rated 10,000 mCd but only over a very narrow angle.

    The Perfect LED Light - Garry Petrie

    The perfect LED light is designed for cavers who want an efficient, uniform and constant bright light for caving. This article contains some very specific technical information and it is assumed the reader has a basic understanding of electronics. To build the light, the reader also must have some experience soldering, drilling, wiring and cutting small objects.

    Pocket LED Light

    This is a pocket-sized LED flashlight operating with only one AAA battery. However, the super high luminosity LEDs(blue,green or white) require at least 3.5 volts of forward voltage. This flashlight is boosting input voltage up to operating voltage of a LED with simple DC-DC converter.

    Single cell LED flashlight

    High efficiency white LEDs have advanced to the point where they can replace glow bulbs and other light sources not only as indicators, but also for illumination. While many of the claims made about the LEDs' efficiency, light quality, lifetime and economy are mostly exaggeration, the truth is that for very low light levels they are now competitive.

    Seven Component Regulated LED Lamp

    This is a minimal-parts lamp made with four white LEDs. It features regulated light output from 10V to 20V and works well as a desk lamp or flashlight. The lamp is still working perfectly 16 years after it was first built.