>> If there is a paddlewiser with circuit design knowledge she may be able to explain how to design a circuit for multiple green LEDs that will work with readily availabe power sources. >> >From what I have read on the Web, you get more even brightness by wiring multiple LEDs in series than in parallel. Here's how: The LEDs should have a forward voltage and a forward current marked on the package. Add up all the forward voltages and subtract them from the voltage of your power source. What remains is the voltage drop across your series resistor. To find the size of the resistor in ohms, divide the voltage across the resistor by the forward current in amps. For instance, suppose you have three LEDs in series with a forward voltage drop of 2.1 volts each, which adds up to 6.3 volts. Since your power source must be larger than the total voltage drops across the LEDs, you choose to use a 9V battery. This makes the voltage drop across the series resister 9V - 6.3V = 2.7V. The series resistor controls the current in the LEDs. The current in a series circuit is the same everywhere, so if the optimum forward voltage for the LEDs is 30mA (0.030A), that is what you also want in the resistor. Dividing the voltage across the resistor by the desired current gives 2.7V / 0.03A = 90 ohms as the size of the resistor. In practice, anything from about 75 to 110 ohms should work, but since the voltage in the battery will drop as it ages, I suggest staying slightly on the small side, say, 82 ohms. The rule of thumb for adjusting the brightness of the LEDs is to increase the value of the resistor to decrease the brightness of the LEDs and vice-versa. However, you should be careful not exceed the maximum forward current of the LEDs, which is typically around 50mA. Wire the LEDs together anode to cathode, wire the resistor anywhere in the circuit, and then connect the anode side of the circuit to the positive side of the battery and the cathode side of the circuit to the negative side of the battery. Tip: If you want to play with the brightness of the LEDs by changing the size of the resistor, place the resistor close to the battery, where it should be most accessible, rather than near the LEDs. For my wife's kayak, I am thinking of running a wire from the LED in the compass through the deck and forward bulkhead, and fastening the battery compartment (with switch) to the inside of the cockpit. The series resistor will be in the battery compartment, so I won't have to take the compass apart to change it. I might even add a trimpot in series with the resistor for easy brightness adjustment. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Remeber that CURRENT, not Voltage (like an incandescent bulb) is the critical parameter. cu ----- Original Message ----- *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Right. The brightness of an LED is determined by the current passing through it. The larger the series resistor (in ohms), the smaller the current, and vice versa. Chuck Holst -----Original Message----- From: Bob Denton [mailto:bdenton_at_aquagulf.com] Sent: Thursday, June 24, 1999 2:35 PM To: Chuck Holst; 'Paddlewise' Subject: Re: [Paddlewise] LEDs was Night Vision Remeber that CURRENT, not Voltage (like an incandescent bulb) is the critical parameter. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
> > >From what I have read on the Web, you get more even brightness by > wiring multiple LEDs in series than in parallel. Here's how: > ====== i am making a pannel of 36 closely spaced jumbo red leds. (2500 mcd each) anyone got tips on how to attach them to a circuit board so that they point with parallel centerlines? say +/- 1 degree? do any of the 6-led flashlights have 2 inch diameter optics? not to bright here,, yet. cu, bliven *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
At 08:56 PM 6/24/99 -0400, Larry Bliven wrote: >i am making a pannel of 36 closely spaced jumbo red leds. (2500 mcd each) > >anyone got tips on how to attach them to a circuit board so that they point >with parallel centerlines? say +/- 1 degree? Hi Larry et al! The base of the LED (where the leads come out) is nominally the reference plane, and the emission peak of most devices is perpendicular to it. Find a chunk of pre-drilled "breadboard" material with holes on 0.1 inch centers, and copper pads on only one side, or with no copper at all. Use a tiny dab of superglue to mount the LEDs with their base flush against the unclad side of the PCB. (sometimes the base will have little "feet" molded into it; in this case, be sure all of the feet are in contact with the circuit board) Carefully bend the LED leads to form your interconnecting circuitry, and solder using a minimum amount of heat. This procedure will get you as close to having all of the diodes emitting on the same axis as is reasonably achievable. If you need better accuracy, you will have to use a photometer and adjust each diode individually, which is probably not worth the bother. Hope this helps a bit! ByeBye! S. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
>> ====== i am making a pannel of 36 closely spaced jumbo red leds. (2500 mcd each) anyone got tips on how to attach them to a circuit board so that they point with parallel centerlines? say +/- 1 degree? >> Have you tried simply butting them tightly against the circuit board and soldering on the opposite side? I should think tolerances on the LED packages would be tight enough to do that and be within one degree, especially if there were no solder traces running under the LEDs. >> do any of the 6-led flashlights have 2 inch diameter optics? not to bright here,, yet. cu, bliven >> See http://www.ndsproducts.com/ledlite.html. It appears that both the 3-LED and 6-LED flashlights have the same 0.97-inch outside diameter lamp housing. The illustration of the lamps on the 3-LED flashlight appears to show jumpers where the other three LEDs would fit in the 6-LED flashlight. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
I'm assuming you're putting them in a hexagon with 4 LEDs on the outside segments. Get a piece of that circuit board with all the predrilled/pretinned holes and put all your LEDs in. Pull them down tight to the circuit board. Just solder cathode-to-anode in a spiral and connect the outermost lead and the innermost lead that aren't connected to anything else. Shawn Larry Bliven wrote: >i am making a pannel of 36 closely spaced jumbo red leds. (2500 mcd >each) > >anyone got tips on how to attach them to a circuit board so that they >point with parallel centerlines? say +/- 1 degree? 0 ____©/______ ~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ Baker Brothers 0 Brews & Boats http://www.missoulaconcrete/shawn/ Shawn W. Baker mailto://baker_at_montana.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Putting all 36 LEDs in series would require at least an 80-volt power source! I suggest a series-parallel circuit with a series resistor in each leg. See also http://www2.whidbey.net/optoinfo/LED_FAQ.html#Q3. Chuck Holst -----Original Message----- From: baker [mailto:baker_at_montana.com] Sent: Friday, June 25, 1999 12:22 PM To: Paddlewise Subject: Re: [Paddlewise] LEDs was Night Vision I'm assuming you're putting them in a hexagon with 4 LEDs on the outside segments. Get a piece of that circuit board with all the predrilled/pretinned holes and put all your LEDs in. Pull them down tight to the circuit board. Just solder cathode-to-anode in a spiral and connect the outermost lead and the innermost lead that aren't connected to anything else. Shawn Larry Bliven wrote: >i am making a pannel of 36 closely spaced jumbo red leds. (2500 mcd each) > >anyone got tips on how to attach them to a circuit board so that they >point with parallel centerlines? say +/- 1 degree? *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Chuck and others, thanks for the links to night vision and LED info. the material helps me to spin up faster and will eventually led to safer kayaking. as a passing note, interesting photography can be done with LED's and digital cameras at shutter speeds in the range of 1/10,000 to 1/100,000 s. cu, bliven *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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