Today we will be starting our adventure into the deeply complex, yet totally incredible world of LED Matrices. This post will be the first of an entire Arduino Matrix Programming series by Circuit Specialists. Make sure you subscribe to our facebook, twitter, and newsletter to keep yourself updated!

First things first, what the heck is an LED matrix, and how does it work??

Simply put, an LED matrix is a grid of lights arranged into rows and columns. LED stands for Light Emitting Diode, so like with other diodes, electricity flows through it in only one direction – from anode(+) to cathode(-); doing so illuminates the light.

By arranging the anodes (positive side) and cathodes (negative side) in a particular way, we can achieve a matrix and call upon each LED individually by sending high and low signals from our arduino device.

Led matrices come in two arrangements. Common-row anode (left) and common-row cathode (right).

Common Annode vs Common Cathode

The difference between these two configurations determine how you would call on a specific LED. With common-row anode (left), the current sources (positive voltage) are attached to rows A – D. Currents sinks (negative voltage, ground) are attached to columns 1 – 4.

Conversely, with common-row cathode (right) the current sinks (negative voltage, ground) are attached to rows A – D and currents sources (positive voltage) runs through columns 1 – 4.

Applying this knowledge, to light the top-right LED (A,4) in a common-row cathode matrix you would feed positive voltage to column 4 and connect row A to ground.

We will be building this arrangement of common-row cathode matrix in this tutorial.

Step 1: The Parts
To build this matrix, we will need a few things to get us started.

1 – Prototyping Board
2 – 8 Pin Headers
8 – 200ohm resistors
64 – Red LEDs

Some other essential supplies include: Soldering iron, Solder, Desoldering wire / rosin flux (just in case), wire (we recommend 2 different colors to stay organized), Heat shrink tubing (optional). We also recommend keeping a multimeter close by for testing purposes.

This will get the matrix built, later we will discuss what’s needed to get it running.

Step 2: The LEDs

We’re going to be using a total of 64 5mm Red LEDs, it never hurts to have some extra though. We have a pack of 100 5mm red LEDs you can get for only $1.65.


Make sure you note which side is the cathode(-) and the anode(+). Hint: it’s the long side on bulbs from Circuit Specialists.LEDOr, you could always give it a quick test! Make sure you use a resistor!

test led cathode and anode

Now, we will begin arranging our bulbs on our perf board. We recommend the 3 x 4-1/4″ Solderable Perf Board model: 64-8934.

Solderable Perf Board - 64-8934

Step 3: Arranging the LEDs

Because we’ve opted to use the common-row cathode arrangement in our matrix, we will be inserting the pins of the LEDs into the perf board in a particular fashion. It is extremely important to be diligent in this process.

Arranging LED anodes

As you can see, we’ve opted to keep the long side (anode) on top, because we will be bending them vertically.

Arranging LED cathodes

Now the fun begins….

Step 4: Soldering the Matrix

Our weapon of choice for the soldering portion of this build is the CSI Premier 75w Soldering Station. We will also be taking advantage of the immensely useful ZD10Y Helping Hand System (it makes ALL the difference).

begin soldering leds to matrix solder leds to matrix

Once we’ve successfully soldered a row of cathodes, we can test their conductivity using a multimeter set to continuity mode.

Multimeter Continuity Mode Leads set to each side of the row.multimeter test continuity

Any reading besides “OL” means you have a complete circuit.Multimeter Continuity

Checking our work along the way will save a TON of frustration later.

Now, we will start soldering the anode columns. 

It’s absolutely critical that the anodes DO NOT touch the cathodes. Here, we’re using a screwdriver to assist with the bending process.
Solder anode columns matrixdont cross anode and cathode

Now, let’s check our work again. Connect ground to your rows, and power to your columns… make sure you use a resistor!

A powered breadboard makes this process extra easy, but any breadboard will do.

Use Resistor to test LED

Check led matrix Check led matrix2 Check led matrix3

This is what will happen if you do not use a resistor (blown bulb)….

blown led matrix

Another easy mistake you might want to avoid (doh!)….


This is why desoldering wire and rosin flux are essential parts of your tool kit!

desoldering circuit specialists

This is what it’ll look like when your soldering is complete.

completed led matrix circuitcompleted led matrix

Step 5: Attaching the connectors

Now that our LEDs are arranged and we’ve tested each of the circuits, we will go ahead and attach the 8 pin headers to the perf board.

8 pin headersThen we’ll add some solder to keep the headers secure.

8 pin headers soldered

Now comes the (arguably) most difficult part of this build with regards to soldering skill…. connecting the pins to the rows and columns.

Keep in mind that the pins will be reversed when you flip the board over, so pay close attention to your work.connect headers to rows

headers connected Now we’ll test our connections one by one.
test headers

Then, we move on to the anode side. anode wires matrix

Then a little heat shrink to keep everything neat. heat shrink connections

As you probably noticed, I initially forgot something very important…. THE RESISTORS!!

Try to avoid this, and get them in the power lines from the start.

resistors in matrix top resistors in matrix

Okay, much better… now we can power up the unit!

8x8 LED Matrix Powered ON

Looks great! Now we can start learning how to program the matrix using the OSEPP Uno R3 – Arduino compatible board!

We will begin this lesson next week. Make sure you subscribe to keep updated!

Particle Photon hand

Introducing the Photon Particle – New Compact IoT Device

We’re proud to announce that Circuit Specialists is now stocking the increasingly popular IoT (internet of things) device, the Particle Photon.



The Particle Photon is a tiny Wi-Fi enabled development kit that’s perfect for creating projects and products for the Internet of Things. It’s easy to use, it’s powerful, and it’s connected to the cloud.

The tools that make up the Photon’s ecosystem are designed to let you build and create; whether you’re an embedded engineer, web developer, Arduino enthusiast, or IoT entrepreneur. You’ll be able to write your firmware in a web or local IDE, deploy it over the air, and build your web and mobile apps with ParticleJS and Mobile SDKs.

Particle Photon Pin Markings Diagram


To get you started quickly, Particle adds a rock solid 3.3VDC SMPS power supply, RF and user interface components to the PØ on a small single-sided PCB. The design is open source, so when you’re ready to integrate the Photon into your product, you can.

The board itself uses a Broadcom wi-fi chip (one that can be found in Nest Protect, LIFX, and Amazon Dash) alongside a powerful STM32 ARM Cortex M3 microcontroller.


For more information, check out the full Particle Photon Datasheet .

Visit Circuit Specialists to purchase your own Particle Photon!

OSEPP Uno R3 Plus VS Official Arduino UNO

What is the Difference between the OSEPP UNO R3 Plus and the Arduino UNO?

Since the first Arduino was introduced in 2005, novices and professionals alike have had an inexpensive and easy way to create devices that interact with their environment via sensors and actuators. Being an open-source development platform, the Arduino community has been presented with a massive selection of compatible hardware.

Here at Circuit Specialists, we are proud to be an active participating member of the Arduino community. Our team of in-house electronics geeks have successfully created a few different Arduino based projects and are anxious to produce even more.

We are currently one of a few local authorized distributors for OSEPP’s line of excellent Arduino-compatible hardware. With identical technical specifications and nearly identical components, we believe that the OSEPP line is an excellent alternative to Arduino/Genuino products.

We’re writing this blog to compare the OSEPP Uno R3 Plus Arduino-compatible board with the official lineup of Arduino single-board computers. We chose to include the Arduino Uno SMD edition as well, since it has a comparable board layout (with SMD).

“The Arduino Uno SMD is a version of the Arduino Uno, but uses a surface mount version of the Atmega328P instead of the through-hole version. This version was made in response to a shortage in supply of the through-hole Atmega328P. The board is based on the ATmega328 (datasheet).”

The board is identical to the PTH version of the Uno, but you won’t be able to remove the ATmega microcontroller without some hot-air (though this change shouldn’t affect most users). The mapping for the Atmega8, 168, and 328 is identical.

OSEPP Uno R3 Plus Specs

Microcontroller: ATmega328P
Clock Speed: 16 MHz
Flash Memory: 32 KB
Operating Voltage: 5V
Input Voltage: 6-12 V
Digital I/O Pin Count: 14 (including 6 for PWM output)
Analog Input Pin Count: 6
Dimensions: 2.95” x 2.13”
Power Source: USB or external DC power supply
Price: $24.95 at Circuit Specialists
Specs from: OSEPP

OSEPP Uno R3 Plus Front
OSEPP Uno R3 Plus Back
OSEPP Uno R3 Plus Atmel Mega328P Chip
OSEPP Uno R3 Plus Parts Diagram

Arduino UNO R3 SMD Specs

Microcontroller: ATmega328P
Clock Speed: 16 MHz
Flash Memory: 32 KB
Operating Voltage: 5V
Input Voltage: 7-12 V
Digital I/O Pin Count: 14 (including 6 for PWM output)
Analog Input Pin Count: 6
Dimensions: 2.7” x 2.1”
Power Source: USB or external DC power supply
Price: $29.95 from Sparkfun
Specs from: Arduino

Arduino UNO SMD Front - Source:
Arduino UNO SMD Back - Source:
Arduino UNO SMD Atmel Mega328P Microporcessor Chip - Source: stevielaner

Arduino UNO R3 Specs

Microcontroller: ATmega328P-PU
Clock Speed: 16 MHz
Flash Memory: 32 KB
Operating Voltage: 5V
Input Voltage: 7-12 V
Digital I/O Pin Count: 14 (including 6 for PWM output)
Analog Input Pin Count: 6
Dimensions: 2.7” x 2.1”
Power Source: USB or external DC power supply
Price: $24.95 from Arduino USA
Specs from: Arduino

Arduino UNO R3 Front - Source:
Arduino UNO R3 Back - Source:
Arduino UNO R3 Atmel ATMEGA328P-PU

As you can see, the OSEPP stacks right up next to the genuine Arduino products, and uses all of the same programming software. With only a slight difference in size, people shopping for Arduino-compatible hardware can feel comfortable purchasing any of the OSEPP products offered by Circuit Specialists.

Note: In our research we did find some users were having a slight issue when uploading code to their devices. Luckily OSEPP provided a response and an easy fix to this issue: “If your sketch does not load properly using the Arduino Uno selection, please select Arduino Duemilanove or ‘Nano w/ Atmega328.’” See the full tutorial for additional information.

And for those of you who love schematics…

OSEPP Uno R3 Plus Schematic - Source: OSEPP
Arduino UNO SMD Edition Schematic - Source:
Arduino UNO Rev3 Schematic - Source:
Electroboom ft. Circuit Specialists

How to Make an Industrial Grade Nightlight – Via ElectroBOOM

If you haven’t already seen ElectroBOOM’s YouTube channel, we suggest you do so immediately.  Not only are his videos educational and inspirational, they’re also ridiculously hilarious. It’s not uncommon to see your host Mehdi give a talk about circuitry and electrical theory, before sending a live charge straight through himself!

We recently teamed up with Mehdi to get him some some new gear to work with, as well as pass along a special offer to his subscribers…

"But first I have to thank Circuit Specialists for providing me with some magnificent tools I was craving for. Make sure to visit them for the equipment you need and use the promotion code “ElectroBOOM” for an additional 5% discount till the end of February 2016."

In this week’s build video, “Making an Industrial Grade Night Light”, Mehdi teaches you how to assemble your very own “reliable night light for your nights behind enemy lines.” A device fit for a “Hells Angel’s biker staying overnight in an abandoned factory… who’s afraid of the dark.”

This is the BlackJack SolderWerks Hot Air & Soldering Station Mehdi uses in the video.

Make sure you keep updated with us!

Until Next Time,
Circuit Specialists


CSI Premier 75W Soldering Bundle – Reviewed By ToddFun

The CSI Premier 75W Soldering Station is one of the most popular and well equipped soldering kits we offer here at Circuit Specialists.

We recently invited one of our favorite YouTuber / Blogger’s, ToddFun, an opportunity to dive into the nitty-gritty details of the 75w soldering bundle and included accessories. Being a man with incredible attention to detail, ToddFun’s review is extremely comprehensive and provides a complete overview of what to expect when purchasing this kit from us.

Sparing no detail, ToddFun covers the in's and out's of the CSI Premier 75w Bundle in this 57-Minute YouTube demonstration and accompanying blog.

For those of you that would like to get even deeper into the CSI 75W Station, ToddFun even published a full tear-down video and blog.

How To Build Your own guitar pedal!

Today I’m going to teach you how to build a guitar pedal. For the last month my friend has been begging me to build him a TS808 clone. If you do not know what a TS808 is, it is a very popular (and somewhat simple) distortion pedal. So I did what I always do when I start a project, I looked it up on google. As it turns out, the DIY guitar pedal community is huge! A lot of people agreed that the TS808 was a great beginners pedal build, and in my opinion guitar pedals are great intro to circuitry. So if you’re just starting out and don’t want to build the classic rc car or clock that everyone has to make in the engineering 101 college class, then this may just be your project.

After getting all the schematics and parts lists together I went on the hunt for my supplies. Of course Circuit Specialists had about 99% of the parts, the only parts I had to hunt down was the 1/4” audio jacks (you’ll need two), a two pin foot switch. I picked them up from my local guitar center. Those two parts were the only ones I could not find at Circuit Specialists and if that changes ill update the blog with the new parts list. All the parts were really easy to find/order, and I managed to get everything I needed in about 3 days. In terms of the parts I personally used I deviated a little bit (because why make my own if I cant mod it?). But the parts that I listed is the classic ts808 clone. All the parts together ended up running me about 30 bucks. Considering retail of a TS808 is $180 I thought this was pretty good deal.

Now lets get down to the build. I started out with a little 20 hole perfboard and started figuring out where to lay everything. I put the ICS smack in the middle because, from the schematics, everything else seems to be equal on each corresponding side of the ics. I’ve uploaded pictures so you could tell where everything is at on my board. With the 20 hole perfboard I was able to fit everything on it perfectly. I recommend, if you wanna upgrade and add things, to buy a bigger perfboard. Remember if you upgrade the size then you have to upgrade the size of the pedal housing. In terms of soldering, any of our soldering irons we sell would work well for putting together perfboards, there is also a PCB schematic you can make. Etching a pcb is actually surprisingly easy, and makes everything much easier when putting it together. We sell the pcb kit if you would rather etch your pcb. Another benefit of a pcb is that it’ll look much prettier. You can see my board kind of looks like a Frankenstein of weird parts and oddly put together. You wont get that issue with a pcb.  I personally just followed the PCB schematics for the board because it seemed like good placement, and it made everything a bit easier.

Once I finished the soldering of the board I start on wiring up the body. For this you will need a drill. I found it easier to use a drill press, but I have no doubt a normal drill can do this. Since we’re using a 1/4” jack use a 1/4” drill bit. Drill on each side of the case, I like to not make the holes line up. Why? because, especially in the smaller cases, the jacks will touch each other. This is especially true in the smaller 1590a cases that you might start using soon. Now, you can either find a jack for the 5v power supply, and then drill the hole for it, or you can use a 5v battery, I chose the battery because I have the room for it in the case. After that simply drill a hole on the top for your switch. Before putting everything on, paint it. This is where you can do pretty much whatever you want, from multiple coats of airbrush, to some spray paint, it doesn’t really matter.

After all this is done, put your components inside. Most people tend to fasten it with an epoxy or super glue. This will help prevent shorts, as well as just keep everything neat. Ill personally be adding the epoxy before I give it to my friend. I’m quite new to these types of projects so it took me about 20-30 hours to finish.  However, I learned a bunch in the process and it was an extremely fun and rewarding project.

Parts List:

What instruments I used for this project:

UPDATE: Banana PI M2 3D Printed Case

A few months ago we drew up a 3D printed case for the Banana Pi M2 single-board computer.  We uploaded it to the 3D printing site Thingiverse for others to print and use.  There have been a few revisions created based on our design and recently a user uploaded a two piece Banana Pi M2 case that is a tremendous improvement over the six piece version we had originally created.

We used the Robox 3D Printer and ABS printer filament to print the newer design and it printed quite well.   It only required a very small amount of sanding on one of the flanges on the lid to make it fit to the base.  The case fits tightly as printed, though we may add holes for bolts in a future design, and it certainly is a workable case as printed.


Thingiverse and their 3D community is a valuable asset to the 3D printing world and anyone considering our Robox 3D printer should consider joining in on this great resource.

UPDATE: CIRCUITSPECIALISTS.COM AT ASU EPROJECT FORUM continues to partner with the Arizona State University eProjects this year.  Our team members have been hard at work this semester on the project that we devised for them.  We have been proud to work with our team during this semester and we are impressed with the work that they have done.  On December 4th our eProject Team presented the progress that they have made on the Banana Pi M2 Home Automation Project.

eproject team

The students have been hard at work interfacing temperature, alarm sensors, and a  HD camera onto the Banana Pi M2. They have made great strides in making all of the components talk to each other.  In the next semester they will be fine tuning the connections, writing the base software, and tying it all together with the 7 inch LCD touchscreen that is available for the Banana Pi computers.

mission statement

We are confident that our eProject student team members will be able to bring it all together into a working development project that we will be offering on our website when it is finished.  I admire the dedication and enthusiasm shown by the team during this project.   Stay tuned for more on this project in the months ahead.

Banana Pi LCD Display Setup

In this tutorial we’ll be setting up the LCD display and the Raspbian OS for the LCD display. We’re using the 7” LCD monitor/touch display and the Banana Pi M2.

Step 1) First we’ll set up the Raspbian OS.

  1. Connect the MicroSD card to your computer and locate the Raspbian OS (LCD) image.
  2. Click the Google Drive logo and download the image (this may take awhile depending on your internet connection). Make sure you download the version for LCDs — the LCD will not work if you have the version for HDMI.

Step 2) If this is your first time setting up a Banana Pi, we recommend going over our first banana pi tutorial.

Windows users will use Win32DiskImager or a similar program to burn the image file to the SD card.

If you’re using a Mac or Linux follow these steps:

  1. Open up your terminal by
  • opening up your finder
  • selecting applications
  • typing in “terminal”
  • open the application with the >_ logo
  1. To find your SD card on your computer. Type in (diskutil list) in the terminal without the parentheses. This will give you a list of your storage devices.  Locate the name of your SD card that you inserted earlier.
  2. Un-mount the card by entering the following command: (diskutil umountDisk /dev/disk1). This is just an example file path, your root file will be located above the storage information of your SD card. In this case mine was /dev/disk.
  3. Once you’ve unmounted the card, run the data dump command to burn the image to the SD card: (sudo dd bs=1m if=~/Downloads/rasbian.img of=/dev/rdisk1).  For this command replace the “/Downloads/rasbian.img” with the file path the raspbian image file located on your machine.  Also replace the “/dev/rdisk1” with the path that you raplaced in step 3- make sure to keep the “r” before the disk#.
  4. Enter your password and wait for the data dump to finish.
  5. Eject your disk (sudo diskutil eject /dev/rdisk1), then replace the filepath with the one you replaced at the end of step 4.

Step 3) Next we are going to connect the Banana Pi 7” LCD display. The first step is to take the ribbon cable and connect it to the port near the Banana Pi logo (the one that has the long black tab). To do this simply lift the black tab and carefully insert the ribbon and then close the black tab, securing the ribbon in place. Be sure to have the blue side (with the labels) facing the Ethernet port.

Step 4) After connecting the ribbon to the Banana Pi, we need to connect the ribbon to the LCD display. Locate the corresponding port near the bottom of the board on the back of the LCD module. Flip open the tab and insert the ribbon with the blue side (without the labels) facing away from the LCD. Once more, secure the ribbon by closing the tab.  When you’re finished with this step, it should look like this.

Display banana pi

Step 5) Once this is done insert your SD card back into the BPi and power it up using the 5V power adapter. Because the micro-USB cannot support all of the functionality on the board — especially the LCD display — we prefer to use a 5V power adapter. Once you’ve connected the power supply, your LCD display should be ready for use.

Measure AC Current with a Digital Panel Meter (DPM)

Digital Panel Meters (DPMs) are strictly DC meters due to the digital circuitry used. Oftentimes it is desired to utilize a DPM to measure AC voltages and currents to take advantage of the improved accuracy and readability of a DPM. This application note will describe a method to accurately display AC current values on a DPM using a current transformer.

The PM128E Digital Panel Meter from Circuit Specialists is ideal for this application, as it is designed to use in a system that has the measured signal isolated from the power supply voltage. The application is for a 0-20 Amp AC meter powered by an external 9 volt battery. This application could also be powered by a “wall-wart” type of AC adapter if desired.

The PM128E DPM is a universal unit with all built in divider resistors and rectifier circuitry to allow AC voltage measurements with no external components required. This meter can be used to display AC current values with the use of a low cost current transformer and load resistor. The current transformer used is a low cost device with a 1000:1 current ratio capable of operation from 0-100 Amps.

A wire with the the AC current to be measured is simply passed through the center of the transformer with the transformer secondary winding connected across a 1.1K ¼ watt resistor so that the transformed current value will be converted to a voltage that can be read by the PM128E DPM in AC voltage mode of operation.

The settings for the PM128E meter should be J3 and J5 shorted with the P1 decimal point location shorted and the AC and 200V points also shorted. This will put the DPM in AC voltage measuring mode with a 200 V full scale reading and set for operation from an isolated 9 V DC power source. The display will read in AC Amps with 0.1 Amp resolution.

The complete implementation of this circuit is included for reference.


This application note has shown how a Digital Panel Meter may be used to measure and display AC current values using a low cost current transformer.

Simply smart circuitry since 1971.