Update2: I have been receiving feedback that I can use eBay suppliers to lower my price on the MAX7219. I had previously considered that option, but after some research I have found that a lot of people are receiving counterfeits on eBay. While some counterfeits may work, their reliability is questionable and that would make my product unreliable. I do not believe that it is “good business” to support businesses and companies which pirate technology and sell it as if it were legitimate. I sincerely hope everyone understands why I am skeptical about using an unknown suppler for parts. Here is a good forum post about coming across the fake variety: http://www.picaxeforum.co.uk/showthread.php?22481-Real-or-fake The more units I can sell initially will increase my per-part discount, which allow me to lower my selling price.
For example if you look at the first picture above, the line across the top is inline with pin 2. If you do a search on eBay or even Google image search you can see that they lines up with pin 3. Also mine has a notch and the eBay ones all have a dimple. Not to mention there is no way someone can go to Maxim and get a price much lower then their lowest price they have.
Last year I came across the MAZ7219\AS1107 LED Driver. This great little IC can drive a 7 segment display or an 8x8 matrix of LEDs. After some research, I noticed that most LED Matrices on the market are driven with simple shift registers which sole function is to reduce the GPIO pins used by a microcontroller. The AS1107 does this in addition to adding SPI control, daisy chaining capability, and single resistor brightness control. The AS1107 also takes care of refreshing the LEDs so the microcontroller isn’t burdened with this task as well. All this and there is a ready-made Arduino library for this IC.
This kit comes with everything you need to make and control an LED Matrix from your own microcontroller. It comes with all the SMD parts pre-soldered. All you need to do is solder the header pins and the LED Matrix to the board. This kit can also be a great way to practice through-hole soldering.
All documentation will be available at http://friedcircuits.us/docs/led-matrix-link/.
All design files will be posted on http://www.github.com/friedcircuits after the fundraiser.
A code example for scrolling text will be available on the website.
• Red 8x8 3mm LED Matrix • Runs on 2.7v to 5.5v with AS1107 from AMS • Ready to use Arduino Library: http://playground.arduino.cc/Main/LedControl • Easy to use • Daisy Chain up to 8 modules with no additional wiring or library modifications. o More than 8 modules may be daisy chained, however this isn't supported in the stock Arduino library. It has been done before and the Arduino forums should be helpful if this is what you are looking to do. Also the more modules affect performance. View my findings here: http://www.mobilewill.us/2013/04/led-matrix-wedding-and-twitter.html • The brightness can be adjusted in software and you can change the 33k resistor to set the max brightness. The current 33k Ohm resistor allows you run 3-4 from USB power. Using the USB Tester and OLED Backpack I measured 225mA for 2 displays fully on at max brightness. (I was actually able to do all 8 but it reduced the brightness a tad.)
• PCB with AS1107 • 8x8 LED Matrix • Right angle female header (unsoldered) • Right angle male header (unsoldered)
Note: You can buy the LED Matrix Master which is the same form factor as the LED Matrix. It has an Atmega328p microcontroller that attaches directly to the LED Matrix Link. https://www.tindie.com/products/FriedCircuits/led-matrix-master/
Follow us on twitter @friedcircuits.
Acacio | Feb. 12, 2014
Michael | Jan. 14, 2014
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