To begin your calculations, you need to know the voltage and amperage of your power supply. I didn't trust the power rating of my 12 volt DC power supply, so I tested it with my multimeter. Good thing I did, it was cranking out 21.5 volts.
Nearly twice as much as it was rated for! The sad fact is most power supplys put out more voltage than they say.
I reccomend you test your power supply so you know its exact voltage. The amperage of your power supply does not matter as long as it is above the amperage your leds are using. Now you need to know the voltage and amperage of of your leds. My leds had a running voltage 3.0-3.5 volts and an amperage of 20 mA or.02 amps.
To start, we need to figure out how many leds will be in series. To do that, divide your power supply voltage by your leds maximum and minimum voltage.
Use these portable battery power supplies for 12V LED strip lights or other 12 VDC products. The AA battery holders use 8 cells and are available in a slim style with mounting holes, double-sided compact style, double-sided wide style, or with a cover and on/off switch. Each battery holder has a 5.5mm barrel connector. Run time will vary based on power draw and battery capacity.
![Sign Sign](/uploads/1/2/5/3/125378711/856514706.jpg)
In my case, it was 21.5 / 3 = 7.16 and 21.5 / 3.5 = 6.14. You need to pick a value between these numbers or lower. I picked 7 so 7 leds will be soldered in series. Next we need to calculate the maximum amount of leds you can have running on your power supply.
My power suppy puts out 2.5 amps max. So all you do is divide the max amps of you power supply by the amperage of your leds.
The amperage of your leds needs to be in amps not milliamps. Remember there is 1000 milliamps in 1 amp. I my case it was 2.5 /.02 = 125. This means I can have 125 rows of 7 leds in series. That makes a grand total of 875 leds.
You can use less than your maximum amount of leds as long as the number of leds in seris is the same. If you need help with your calculations, leave a comment and I will help you. Now we can begin placing the leds on the perf board. Using your excel drawing as a guide, put the leds legs through the holes in the perf board. The polarity doesn't matter because we will be removing the leds and marking their positions. It will thake some repositioning to get the leds to look good. When you are satisfied with the shape of you letters, begin removing the leds and marking where their legs were with a sharpie(pic 2 & 3). When you finish, transfer the design to the back by marking the other side of the hole.
When you're done, it will be a mirror image of the design(pic 4). To begin, mark the polarity of the marked holes with a sharpie. I just put a red dot next to the positive hole. When marking the polarity, remember that the leds will be connected positive to negitive and will be the number of leds we calculated for series earlier. Next, put the legs of the leds through the proper holes. Hold the led tightly and bend the leads over so the led is securely held in place.
Repeat the process with another led and snip the leds so they overlap slightly. Solder the spot where the leds overlap and repeat the process with all the leds in that row of series. You will probably have some letters where the number of leds in series is greater than the number of holes for leds left for leds.
When this happens you need a resistor. I didn't have a resistor so I made a 'resistor'. The 'resistor' is a led or leds soldered the back and and wraped in tape so it emmits no light. You still need to have the same number of leds in the series and the 'resistor' leds count as leds toward your led total. (example: You need 7 leds in series. You have 3 on the front so you need 4 leds as a 'resistor' on the back.
3 + 4 = 7) All you need to do now is connect the sign to your power supply and you're done! Thanks for the tip, I have never used perfboard. My experience with soldering and electronics amounts to 2 altoids flashlights and a star constellation, a beginner for sure.
![Led Led](http://cdn.shopify.com/s/files/1/0104/1750/4314/products/plelrxteu-gw_1024x1024.jpg?v=1530131083)
I am planning on making signs for my nieces and nephews. Do you have a good resource for low cost perfobard, online I suppose? I looked for some at Frys but they were quite expensive, since I am making 4 of these I'm trying to keep the cost down.
Also, did you use 3mm or 5mm LEDs? You said you recommend diffused LEDs, would you say the same if you were to change the color of the sign to say, green or blue? I appreciate the reply! Thanks a lot for you help on this, one last question. I have been trolling ebay and trying to find perfboard similar to yours which I have found. What I have not been able to find is the metal that goes over the perfboard. How did you make the nice cover for it?
Also how did you mount the sign? I was thinking of using a project box but I don't know how I could get a cover with predrilled holes such as yours. I ordered my LEDs, mostly diffused but I couldn't find blue/purple in diffused so I settled for low mcd. Would you be able to advise me on the wiring?
My first sign will have these types of LEDs: Size: 5 mm Lens Color: Water clear Emitted Color: Ultra Violet Viewing Angle: Approximately 25 degree Forward Voltage: 3.0 V- 3.2 V Forward Current: 20mA Wave Length (WL):395-400NM Luminous Intensity: 300 mcd-500 mcd Lead Soldering Temperature: 260°C (. The main reason I didn't use perfboard with the pads is because it is not needed. The leds have lond enough leads that I can simplely bend them over. This saves solder not having to connect all the pads and makes coloring the other side easy (Black Sharpie looks dull on the board and shiny on the pads).
Perfboards with the pads are mainly designed for IC's and more advanced circuits. This project is simply lots of leds soldered is series. There is a big differance in price too.
It costed me about $2 for the perfboard in this project, and I have some left over. The perfboard with pads costs $4+ for an amount that I used in this project.
I hope this helps and feel free to ask any other questions you have. This is a well written instructable with great pictures. I have wanted to make led tail-lights for my aging pickup. Older bulb style tail lights are not as bright as the newer models with led tail lights. I am thinking about safety.
Your article is so well written that determining the voltage and amperage is no longer a mystery. I think it will be possible to get the 12 volts at the tail light connection, leaving the bulb intact and operational. Since the leds will be a lot brighter, they will outshine the original bulb and be more visible. Care to write an instructable about upgrading tail lights?? It will be greatly appreciated.
I will vote for you!!
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