I'm designing a high-end LED bulb and need your input.

bean · 10-21-2010, 07:20 PM

I made a couple posts in a thread in the "Dollars and Cents" forum about a LED bulb for my RV that I am designing (I'm a self-taught electrical engineer).

This will be a high-end bulb with extra features such as:
- Constant light output with battery voltage from 11V to 16V.
- Soft start (fades up)
- Low power and nightlight modes (by turning light quickly off and back on)

I just received parts for the prototype it looks good. Full power mode (same lumens as a 921 bulb) pulls 0.4 Amps. Low power mode (which is still pretty bright) pulls 0.2 Amps. And nightlight mode pulls about 0.03 Amps.

I have the different modes working that microcontroller that is easy to program, but is NOT the one that will be in final design (it's too expensive).

I'm looking for ideas for other features that I might design into this. What features would you want in a LED bulb replacement ?

Someone already mentioned a ultra-efficient design, and I may tackle that after this one.

Bean

The_Stuff · 10-21-2010, 08:37 PM

ohhhh. self dimming? sounds good.

LadyWindrider · 10-21-2010, 09:21 PM

How about a time delay for off. That way you could switch it off, the get in the bed before it goes out. Not all RV's have a light handy to the bed. May not need to be a separate feature, just put in a 30 second delay off.

And it needs to be cheap. By the way, processor controlled, what is the power draw when in the "off" mode?

cmhbob · 10-21-2010, 10:48 PM

Between your original idea and windrider's suggestion, I can't think of anything else to add.

The_Stuff · 10-21-2010, 11:34 PM

i dont think he could do such a thing as having it last 30 seconds once the power is off.

bean · 10-22-2010, 07:39 AM

Yeah, this is just a bulb replacement. So I can't have it on when the switch is off. No power. And when the switch is OFF there is no current used.

What I could do is have a slow-off mode where is slowly dims the light until the bulb is off (the switch is still on). Then to turn the light on again you flip it off and on.

Something like this would work:
(switch is off)
Turn switch on - light is in constant on, full brightness mode.
Flip switch off and on - light is in "slow off" mode (5 minutues until full off).
Flip switch again - light is in constant on, half brightness mode.
Flip switch a 3rd time - light is in constant on, night-light mode.

What do you think of that ?

Bean

Fire Instructor · 10-22-2010, 08:17 AM

My experience with some of the replacement LED's curently on the market is a poor fitting "wedge" to snap into the original fixture. My unit uses mostly 921 style bulbs, and the new plastic wedges seem loose and wobbly ... I jammed the end of a tooth-pick (plastic) in a few just to keep them tight!

DageonYar · 10-22-2010, 08:48 AM

Hi Bean,

Some handy information to help in your endeavor.
Super Bright LEDs - LED Information

**Herk7769** · 10-22-2010, 09:28 AM

Quote:

Originally Posted by The_Stuff

i don't think he could do such a thing as having it last 30 seconds once the power is off.

Why? That actually seems easier to do than some of the other ideas. A suitably sized capacitor should be able to provide power to the LED for whatever time you needed. No?

There are actually very cheap AA battery powered LED lights that do something similar. I have a motion activated light (bought at home depot) in the bedroom that we use to provide "getting into (and out of) bed light" without touching anything. I did need to use some black electrician's tape to carefully block the sensor to it would not trip when we rolled over at night but would work when we got up or walked into the room.

The_Stuff · 10-22-2010, 09:48 AM

true but it will feed back into the system to unless it has diodes in it and thats increasing the price per bulb i would assume.

i think bean has it right on with the latest steps of
=====================================
(switch is off)
Turn switch on - light is in constant on, full brightness mode.
Flip switch off and on - light is in "slow off" mode (5 minutues until full off).
Flip switch again - light is in constant on, half brightness mode.
Flip switch a 3rd time - light is in constant on, night-light mode

acadianbob · 10-22-2010, 10:08 AM

I think that there is a risk of it getting too complicated versus all of the features contemplated. I don't want to have to pull out an "owners manual" every time I use the trailer to operate the light!

Good luck to you though. There would be a real market for a 921 replacement of high quality. I'll be watching for it!!

DageonYar · 10-22-2010, 10:43 AM

Instead of a complex series of on/off to change the behaviour, maybe just have a DIP switch on the LED panel itself to select the desired behaviour. Normal/Low/Fade Off.

jimh · 10-23-2010, 07:41 AM

the capacitor or a small recharable battery should work. i wouldn't worry abt the feedback. once the switch is off, there isn't any place for it to go. don't need the blocking diodes. how are u accounting for the light. in the finished product, if the bulb is and its' entire circuit is contained within the light socket, how do u keep the reflected light from interfearing with ur sensor? one idea would be to put the sensor in a wall mounted light switch. that would also give u a source of power to keep a processor powered.
once the voltage drops to 11v, is ur circuit going to continue to draw current or are u going to switch it out until the power is removed and restored?
if u used two stages, the power could be applied to one set of led's. the other set could be switched in with a photocell and a switching transistor. time delay, ur back to using a power source...a 9v rechargable bat and a ne555? put it on the second set of led's. or u could size a capacitor that would give u enough energy for the time required (size might restrict u here).
the more u add, the more the cost, the more chances for problems. KISS...

bean · 10-23-2010, 09:40 AM

jimh,
There is no light sensor. The product is just a bulb replacement.
There is a small capacitor that runs the microcontroller for about 2 seconds so it can remember what mode it is in. If the switch is off for more than 2 seconds it starts in normal mode again.

The circuit is not very complecated. A 3.3V regulator, a couple caps, the microcontroller, 9 LEDs, three transistors and some resistors.

The GP0 input on the microcontroller senses when the switch is turned off.

The C1 capacitor keeps the microcontroller running for a couple seconds even when the power is turned off.

The transistors and 20 ohm resistors create a constant current of 125mA through the LEDs regardless of the voltage.

Each string of LEDs draws 125mA plus a some for the microcontroller so total of about 400mA for full power.

Any questions, please ask.

Bean

jimh · 10-23-2010, 11:49 PM

as drawn, i don't see the reason for the microprocessor. are all 3 2N2222 switching transistors tied to the same pin on the microprocessor or is this just simplified? looks like this could be accomplished with just a switch.
does the processor have an internal clock or do u have to supply one?

bean · 10-31-2010, 08:01 PM

I've had some people ask for a high quality, high effecency LED light. So I've decied to re-design the circuit to make it as highly effecient as I can.

I'll post details as I have a chance to test a couple design ideas. I'm hopeing to get to about 250mA to 300mA with the same lumens as a 921 bulb.

The main loss of power in the above circuit is in the 20 ohm resistor and the transistor when the battery voltage is highest (above 12.5V). By using a custom microprocessor controlled "switching" regulator I should be able to recover this wasted power. The design will run cooler too.

Bean

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