I intend on making a project illuminating an acrylic transparent rod. drill holes on both sides and inserting Blue LEDS tight space wired in series or parallel what resistor value and perhaps small switching power supply to make LEDS Blink to prolong batteries and maintain luminosity? I am considering using High end rechargeable double AA batteries guessing 3, in learning that blue LEDS require 3.2 VDC. Power and or a switch must fit into compact area like 2/3 of cigg pack. any ideas? Bottom line long life of batteries and at least mid way luminosity.
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\$\begingroup\$ As you hinted in your tags, a boost converter or constant-current driver would be appropriate for this situation. \$\endgroup\$– uint128_tCommented Mar 21, 2016 at 4:32
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If you wire your LEDs in series, as you say they have a Vf on 3.2 then there is no chance of powering them with 3 AA batteries. You also need to remember that whilst AA batteries do say 1.5V this is a fully charged battery. AA batteries whilst discharging do lose some voltage (I've had AA batteries at 1.35V and they still powered my wireless mouse). Rechargable AA batteries start at 1.2V if they're NiMH's.
You could try using 4 rechargeable AA batteries connected in series, giving you 4.8V supply. You would have to connect the LEDs in parallel however, otherwise the Vf is going to be more than the batteries can supply. For mid-luminosity you probably want around 15-20mA, with 4 batteries and 3.2Vf LEDs then 82 ohms would be fine.
Bottom line, 4 rechargeable AA's connected in series, 2 LEDs in parallel, 82 ohm resistor connected to each LED
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\$\begingroup\$ thank you for your Answer, I will consider that but i am simpler or less parts less rechargeable, perhaps a 9 volt rechargeable, or flat batteries that fit inside a cell phone. So far these are the two blue LEDS specs. Colour : Blue Size (mm) : 5mm Lens Colour : Milk-White Peak Wave Length (nm) : 465~470 Forward Voltage (V) : 3.2 ~ 3.8 Reverse Current (uA) : <=30 Luminous Intensity Typ Iv (mcd) : Average in 5000 Viewing Angle : 120 Degree Absolute Maximum Ratings (Ta=25) Max Power Dissipation : 80mw Max Continuous Forward Current : 30mA Max Peak Forward Current : 75mA Reverse Voltage : 5~6V \$\endgroup\$ Commented Mar 21, 2016 at 10:08
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\$\begingroup\$ The only issue with using a 9V battery is they have less capacity (mAh) than an AA battery so they won't last as long. When i get back to a computer I'll draw a circuit and explain how to calculate it all \$\endgroup\$– user103993Commented Mar 21, 2016 at 10:29
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\$\begingroup\$ amendment changing circuit same 2 blue leds however want them to fade on / off same time. 2 links found on utube may help check his modified schematic , I'll need to add a second LED blue and maybe a 2nd transistor 2n222a i think it's PNP. Bottom line 2 Fading Blue LEDS on off same time compact power , 555 timer. youtube.com/watch?v=qLAi7hkDuYw 3.bp.blogspot.com/-8dh2sGOARuM/TqAbenpiOnI/AAAAAAAABEA/… \$\endgroup\$ Commented Mar 21, 2016 at 12:22
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\$\begingroup\$ What you're asking for is no longer going to be as compact as you like. I can draw you up a circuit but how compact it will be is a different question \$\endgroup\$– user103993Commented Mar 21, 2016 at 12:25
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\$\begingroup\$ Yes please draw a circuit for 2 blue LEDs fading on & off at same time, with whatever components u desire \$\endgroup\$ Commented Mar 21, 2016 at 15:30
