555 Timer Business Cards

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Hello!

So I thought up this cool little project during my last few weeks during my co-op term at Echologics Engineering. I saw everyone had nice, professional looking business cards, and I needed something to springboard myself into PCB design and manufacture. One and one came together, and this idea came about.

There were quite a few idea revisions in my mind before I actually got around to spinning the PCB. Microcontroller? Basic LED’s? No circuitry at all? Finally I got the idea of using a 555 timer (after seeing something about worldwide 555 timer competitions on the EEVBlog) that would be outputting a clock to LED’s, which would flash depending on some external interaction to the timer.

First idea: a photoresistor of course! The external RC circuit worked perfectly in ambient light with a simple 10k photoresistor. I quickly ran into an issue though; if I wanted to use a photoresistor, I would have to make my PCB through hole. I was not able to find one surface mount photoresistor. Therefore, I had to “fabricate” my own! How does one do that?!

Current in parallel with a normal resistor, of course! A phototransistor could act in place of the photoresistor, limiting the current in the RC circuit control for the 555 timer. Some issues with this, of course, is that phototransistors are quite expensive, and I managed to purchase opaque top photoresisors (which Digikey first sent as Red LED’s… D’OH)! After some trial and error with a scope and a breadboard, a working 555 timer, LED blinking, opto-frequency controlled circuit formed.

Then came the digitization! Here is the PCB layout and electrical schematic for my project. I was going to use SEEEDStudio’s Fusion PCB service to create my PCB’s, so I made sure I was using 14-14 spacing for traces. I also increased tolerances for pads and such, just to keep everything safe. Another folly I will learn from this project; don’t use diode type pads for surface mount protection diodes. These special diodes (that are very expensive mind you) are in the mail for tomorrow, and will be exceedingly difficult to solder on, when I could have easily used a much larger SOD package.

The idea behind the circuit is that you lay a 9 volt battery on the terminals, and the circuit then operates as expected (see video). The only issue is with the phototransistor, as it only operates very well in high intensity light (direct sunlight, or a “low” powered laser). It does vary frequency from 0-5 Hz with a bright light source.

The card features my personal info, as well as one of my favourite Tesla quotes on the backside.

And there it is! Just in time for interviews too, one of which I have tomorrow. I hope these turn some heads!

Here’s the card in action!

Best,

Cody

32 thoughts on “555 Timer Business Cards”

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  6. So cool. We’d like to cover this for Mashable. How much does each card cost to make, and how many did you create? Good luck with your interview — let us know how that went!

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  13. Greetings from your neighbour in Toronto! That is really neat! As a fan of Arduino and waiting for my Raspberry Pi in the mail, and having developed a few apps for the Blackberry Playbook… This kind of stuff really gets me excited! I would be so happy if I got a printed PCB business card from someone, so I am sure the people you give it to will keep it and remember you! Great way to differentiate yourself! Awesome job!

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    • I don’t plan on making enough of these to send out randomly, they are meant for employer interviews at places where I would really like to work. Sorry!

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  19. As an experienced electrical engineer, I’d suggest you do not run the three strings of LEDs in parallel, but rather have each set of three LEDs have their own 150 ohm series resistor to Vcc. Otherwise variations in the LED forward voltage will cause uneven or excessive currents (or no current) to flow through each string. You may not be familiar with circuit simulation tools (PSpice or NL5) and worst case analysis (or extreme value analysis) where variations of real world parts are used to check circuit performance versus assuming all parts have the same nominal data sheet value. Thanks, and good luck.

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  22. Hey Cody. I just got started in electrical eng. Love this idea. Not mean to copy you but without knowing pcbs how can i replicate this?

    And even how to incorporate david’s suggestions ?

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