DIY LED Ring Light PCB for Microscopes!

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About: My name is Taylor, I am an electrical repair tech by day and an engineer by night, after work or free time.

I am back and this time I put my board design skills to the test!

In this instructable I show you how I designed my very own microscope ring light and some challenges I encountered along the way. I bought a second microscope for electronics use and unlike my first one it didn't come with a ring light. After a quick google search I found that good ring lights are a bit pricey for almost no reason, maybe I just wasn't looking in the right spot but I just wasn't happy with the prices. I couldn't bring myself to pay even 30 dollars for a light because of what it is. I mean it is basically just a flash light, why do they cost so much? After realizing I didn't want to buy one I thought it would be a fun thing to make myself! I love designing boards and soldering as well as fun projects so let's give it a go! My light features 48 bright white/soft yellow leds that can be turned on in groups or all at once and can be dimmed. It is a really useful attachment that any microscope can benefit from! This project shows you just how useful prototype PCBs are as I ended up making a few mistakes with the first design and had to send out for a second batch with the updates. This could have been very costly if I assumed all was well and ordered dozens of boards the first time around but we'll go over all that along the way! Be sure to check out the PDF for clearer images of the schematic. This project is sponsored by JLC PCB, check out their website and watch my video for more information regarding their services!

Supplies:

Everything needed for this board can be found in the attached files

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Step 1: Watch the Video Covering the Entire Build and Follow the Steps for More Information!

I am trying to up my production value for my projects so any advice and constructive criticism is welcome! This is just a hobby for me but I do want to get better and see where it can go :)

Step 2: First Design.

My goal when making this was to have a very bright and compact ring light with some added features. I wanted to toggle 1 of the 4 groups of leds one at a time or all of them at once. This may not be a desirable feature for everyone but I wanted to throw light at certain angles to illuminate objects differently for certain applications and photography. The control circuitry ate up a fair amount of real estate on my small eagle freemium sized board but that just made it more fun to figure out.

The idea for controlling the leds in the first design was simple really but thanks to my impatience I found myself fixing some issues and adding in features for the second design but we'll dive into that more in a few steps. The 48 leds are in groups of 12 consisting of 3 sets of leds in parallel with 4 in series. Each group is controlled by a transistor and the transistor is controlled by a high signal from a decade counter that shifts its outputs based on a manual (button) clock input. There are 4 groups of leds but we need 5 decade counter outputs to turn on 1-4 and the 5th to turn on all of them. Each transistor base is tied to an output which allows it turn on. How do we use the 5th output to turn on all leds without conflicting with other groups when activated by themselves? Diodes! The 5th output of the counter is tied to 4 diodes with their anodes in parallel and their cathodes running to each transistor base. This allows us to activate all transistors at once without having any current leaking into other bases when 1 of the 4 groups is activated by themselves. The 48 leds require a 12 volt supply (4 leds in series x3v=12v) and the control circuitry requires 5 volts so we use a 12 volt power supply and add a 5 volt linear regulator to drop the voltage to power the control circuits. After soldering everything up it failed to work properly :(. I was bummed at first but I realized that this usually is part of the process when designing boards. You come up with an idea, make it, find the issues and fix them. I have learned to never expect something to work first try and in doing so when something does work first try I am really surprised but its all part of the process. You may be wondering why I designed everything using smd parts and the answer is simple. Since I am using the free version of eagle I am stuck with a max board dimension and it can't be any bigger than what I came up with so everything has to exist on a board that measures in at 90mm with a huge chunk missing in the middle which leaves us with a very small 18mm wide surface area. If I used through hole leds I would have to route around the leads and that would take way too much time. Maybe in the future though? By the way routing etches on a circle was fun.

Step 3: First Design Mistakes and Mods Necessary to Make It Work.

After troubleshooting the first design I realized there were too many mistakes to leave alone. The mistakes are as followed;

  • The clock enable pin for the decade counter was not connected to ground which meant that wouldn't clock
  • The clock sequence was messed up due to skipping Q3 in the schematic
  • The dual package transistors didn't like playing well with each other
  • Diodes running in series with the transistor base resistor didn't allow enough current through to activate the transistors.

In order to make the design work I swapped out the dual package transistors for single package ones, moved the diode cathode position to run in parallel with the base resistor and fixed the mistakes with the control circuit. I used very thin copper wire to run all my mod etches. After I had a working board I loaded all the fixes back into eagle for round 2!

Step 4: Design 2 With Added Features

After addressing all the issues with the first design I went ahead and added an external dimmer using a common anode PWM dimmer I bought off amazon. The first design lacked a dimmer feature and the board was too crowded to add more to it so I experimented with a cheap amazon one and found that it did the trick! Instead of tying all the leds high to 12v they are now tied high to the PWM signal which is an added pad on the board. I cover the dimmer more in my video.

In addition to the dimmer I added resistors to the led groups and pulldown resistors to the transistors base as a 'just in case' measure. They aren't being used as of now but better safe than sorry and I added a tactile switch to the board instead of mounting it externally. The intent originally was to use a case but after seeing just how compact it was I ditched that idea in round 2. I soldered all the leds on followed by all the other parts and tested it and it worked! Just as it should! It is very bright too! If you really want to test your patience go ahead and hand solder a total of 96 fragile leds. They love to melt if you take even just a second too long to solder them. Note that r7-r10 don't have listed values, I used 100 ohm resistors but this value may change depending on your needs. Note that r11-r14 have no values because they aren't being used. Note that c2 and c3 have the wrong values listed. I ended up using 16uf caps not 0.1uf. (all smd caps and resistors are 0805)

Step 5: The Board Works. Now What?

Now its time to make it mountable. In order to do this I used two threaded coupler rods and thumb screws. I borrowed the idea from other lights.

I scuffed up the coupler standoff rods and used two part epoxy to adhere them to the board. If I revisit this project in the future I might plan for the mount on the board level.

Step 6: That's a Wrap!

Yes I cleaned the final product with a lot of alcohol. During assembly and test I used a lot of rosin and should have cleaned a long the way but was too distracted on making it work. I truly hope you enjoyed this instructable as much as I did making it. If I were to make a version 3 of this project I would add a strain relief for the power cord, take the time to implement my own dimmer into the board and plan out the mount better. Other than that I am really excited as to how this turned out and yes it may have been a weird route to take over just buying one but many people fail to realize just how fun and rewarding it is to just DO IT YOURSELF. In the end I did have enough parts for 3 or more complete boards which works out to being cheaper than buying three. If you plan on making this yourself be sure to use jlcpcb.com for your order. You will receive 5 professional boards with your choice of color for just 2 dollars!

Thank you for making it this far and if you liked this project be sure to follow me on here and at my youtube channel! I will see you next time!

youtube- https://www.youtube.com/channel/UC4CMvhUs1LWVNhkU...

jlcpcb- https://www.youtube.com/channel/UC4CMvhUs1LWVNhkU...

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