I need some help modding my engagement ring box to add a battery-powered LED circuit. The diamond that I bought has strong blue fluorescence, so it glows blue when exposed to UV light. I've seen ring boxes for sale that have one or two white LEDs, but I'm thinking adding a single UV LED to the mix will give it a nice bluish hue while keeping the sparkle from the white light.

Can any of you guys help me build a parts list for my circuit? Given the small amount of space and no need for a long run time, I think button batteries make sense.

• Batteries
• 2 white LEDs
• 1 UV LED
• Resistors
• A simple switch

 

It looks like you have your parts list complete. You wouldn't need any more than that. Perhaps use a "Little Dot Accent Light" from superbright as it will stick to the top of the box.

 

It looks like you have your parts list complete. You wouldn't need any more than that. Perhaps use a "Little Dot Accent Light" from superbright as it will stick to the top of the box.

Thank you for the reply. I'm an electronics newbie, so if you can also help me design the actual circuit I'd really appreciate it. I notice those LEDs require a minimum of 9 volts and look really bright in the photos, so 1 natural white and 1 UV would probably suffice considering the LEDs will only be a few inches from the ring. In order to power two of them, should I use (3) CR2032 batteries stacked in series? In that case, I would need to run the LEDs in parallel with a resistor for each, right? Should I use a higher value resistor for the white LED since it is rated at 6000 mcd intensity while the UV is 800?

Edit: I now see they have built in resistors for 9-15 VDC operation, but maybe I could add an additional resistor for the white LED to reduce its brightness a bit?

 

Thank you for the reply. I'm an electronics newbie, so if you can also help me design the actual circuit I'd really appreciate it. I notice those LEDs require a minimum of 9 volts and look really bright in the photos, so 1 natural white and 1 UV would probably suffice considering the LEDs will only be a few inches from the ring. In order to power two of them, should I use (3) CR2032 batteries stacked in series? In that case, I would need to run the LEDs in parallel with a resistor for each, right? Should I use a higher value resistor for the white LED since it is rated at 6000 mcd intensity while the UV is 800?

Edit: I now see they have built in resistors for 9-15 VDC operation, but maybe I could add an additional resistor for the white LED to reduce its brightness a bit?

The resistor is chosen based on the LED forward voltage drop/supply voltage and current for the LED where resistance(R) = (Supply vdc - forward voltage)/current in amps.
So for example lets say you have a
9V supply
An LED with a 3.2V forward voltage
and rated current of 20mA (.02 Amps)
So R=(9-3.2)/.02
or 290 ohm

Then you need to figure out the wattage of the resistor where
Watts(P) = I^2 * R
W = .02^2 *R
or .116 Watts (multiply that x 2 for safety factor) so you need a 1/4W resistor

If the current requirements of the LED's are similar you can run them in series with only 1 resistor BUT with a UV led that might require a 12V+ power source as your power supply must be greater than the combined forward voltage drop of the LED's in the series string.

Post back with your LED forward voltage ratings and current requirements if you need more help.

Note you can also run the LED at less than its current rating to make it dimmer. 20mA LED's are actually pretty bright for something like this.. unless you are gonna pop the question in the dark.

And don't feel bad when she could care less that you had an LED or not or that you actually built an electronic circuit.. She only cares about the ring and how it "shines" on her finger and what her girlfriends will say about it..

 

If I use the Little Dot Accent Lights as recommended by GRNDPNDR, I'm not sure what their forward voltage is as I don't see it listed on the website:
http://www.superbrightleds.com/moreinfo/led-wired-bolts/little-dot-smd-led-accent-light/639/
I'm not experienced enough to know how bright 6000 mcd is, but it sounds really bright for this application. How can I figure out what resistor I should use to dim the white LED, if I don't know the forward voltage of the LED or what value the built-in resistor is?

Do you think I should instead use 3mm or 5mm "Through Hole" LEDs and build the circuit with my own resistors?

As far as her appreciating the LEDs, in this case I think she will because she loves blue fluorescent diamonds, and the UV will show it off. I already purchased one of these keychain UV lights to give her after I give her the ring:
http://www.superbrightleds.com/moreinfo/keychain-lights/keychain-micro-light/366/

 

If you go with the little dots and they are too bright.. Simply just keep adding resistors till you get the brightness you desire.