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.



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

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,....



....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.

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.



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.

Logic Probes for Digital Testing

Digital Test and Measurement Starts with Logic Probe - Any point in a Digital Circuit can be High, Low, Float means TriState. The High Low in a 5V CMOS circuit is just 0V and 5V. In TTL and ECL it is much different

TTL Pulse Reading Logic Probe - This circuit can monitor TTL logic levels. TTL compatible CMOS logic families can also be monitored.

The Test Point could also be Pulsing or have analog values and waveforms, as in Mixed Signal Chips. Here are Logic Probe Circuits you can Build in your own Home Lab.



Simple Logic Probe - Here is a simple Logic Probe using a single chip. The circuits have been designed for the CD4001 CMOS quad NOR gate and CD4011 CMOS NAND gate

Andy Collinson - Logic Probe - This logic probe uses a single CMOS 4001 IC and can display high, low and pulsing outputs.

Homemade Metal Detector Kit

This idea is both for indoor and outdoor use, depends on how you could modify or enhance it. The important reason you ought to build this circuit is to learn building non-ic oscillators, this trains you on L, C, R and Transistor Switching. - delabs



With a handy metal detector you can check beforehand whether there are metal objects in a wall, ceiling or floor. An LED indicates if a metal object is in the vicinity and keeps your simple home projects, simple and safe.

Homemade Metal Detector Kit

Avoid disaster when drilling at home By Ben Godfrey

Ben Godfrey is an electrical engineering student at the University of California, Davis. Ben has written iPhone applications and is a Ham Radio operator.

See also  - Metal Detector Circuits Problem

The Micro Stop - RS232 microcontroller

"These pages are a useful collection of microcontroller RS-232 data acquisition circuits and code. Most of the code on these pages is written in C because it is the language that is definitely the fastest way to produce working applications."

The Micro Stop - RS232 microcontroller



RS232 controlled and RS232 powered DVM-001 voltmeter kit with PC voltage display. This circuit uses a PIC12F675 8-pin microcontroller with built-in analog to digital converter. The circuit also has an op amp and resistor divider network to achieve the 54vdc max input voltage.

Measureall Workbench Test Instrument

This was a Student Project, it is a very basic instruments that could do most of the tasks on a test bench.

The cabinet used, was available as a part of a Hi-Fi DIY System, The Range and Mode switches were Modular Stackable Interlocked MultiPole Switches. The rest of the Interface were wirewound pots, jacks, sockets and plugs. The front panel was Engraved Acrylic.

I wanted it to look well engineered, at least on the outside. It was a total analog instrument except for the digital indication of ICL7107. Thanks to 'Intersil Hot Ideas' Applications Book.

• Diode Thermometer
• Voltmeter Attenuator Rectifier
• Dual Power Supply
• Function Generator using ICL8038

The above belong to an instrument Measureall shown

Bakatronics - DIY Kits and Model Railroads

Bakatronics LLC designs and manufactures innovative electronic circuits for model railroads.  For the last decade Baka has been creating new ways to make your model railroads "come alive". 

Bakatronics - DIY Kits and Model Railroads

The Kits include the Lighthouse Flasher, Emergency Lights, Airport Beacon, Campfire and Super Welder Flash kits All are based on advance micro controller technology and will enhance any railroad.



FK945 Digital Temperature Controller kit

This circuit can be used to control when an appliance or device turns on and off by temperature. 3 Digit Read Out and easy to set buttons.