Printrbot Simple 2016 – Hardware (PCB) explained

This blog post describes the details about the hardware, more specifically the PCB that I have developed for the display component of the new Printrbot Simple 2016. As we believe in Open Source we have published everything under the MIT license. Have a look at the code respository, too.

To give you some context why we have chosen these components please first read my Behind the Scenes report that describes the process of selecting the right components for our purpose.

Block diagram

Let’s have a look at the Block Diagram of the Simple 2016 and how various components are connected. First we have a very clever power management that delivers enough current for all the motors and PCBs but also does that secure and with great efficiency. Next there is the Printrhub, which is the display component of the printer. The hub also controls the Printrboard and the ESP module to communicate with the Printrbot cloud that holds all the projects, materials and settings of the user. Last but not least there is the printer itself, powered by the g2 Printrboard with advanced motor handling features and advanced algorithms for great prints.

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Printrbot Simple 2016 CommStack explained

This is series 3 of the Printrbot Simple Behind the Scenes report. In this post I will go into detail what CommStack is and why we developed it. As you know Printrhub has two MCUs: ESP8266 and Teensy 3.1. There are more details on the hardware design here, but to make it short hier is a block diagram of the setup to get us started:

printrhub_block_diagram

As you can see, MK20DX256 (our main processor) has quite a lot to do. And if you have read the document describing the display system you know, that we cannot block the main loop any time. Because that would mean that the display is unresponsive or worst, the printer does not get new commands and stops the print.

Let’s think about a usage scenario and translate that to tasks of work being done by this system: Starting a print.

If you start a print, you select the print job on the display. MK20 will ask for touches in its main loop and reflects those interactions on the screen. When you press the PRINT button, MK20 checks SD card to see if that file is already downloaded (available on the SD card). If it’s not, MK20 has to ask ESP to download the file. ESP downloads the file and sends the data to MK20 which in turn writes the data to the SD card.

Remember, we don’t want to block the main loop. We need to do that in an asynchronous way. What I mean with that is that we must split that into very small pieces and execute them one after the other in the main loop, but in between we give control back to other parts of the system.

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Printrbot Simple 2016 Display System explained

Over the past few months I have developed the LCD component of the new Printrbot Simple 2016. In this post I want to explain how the display system works. It makes sense you read the Behind the Scenes report of building the Simple 2016 first, as that gives you some context to what I am talking about here.

Early on we decided to use a display with the ILI9341 display driver chip as there is a very fast display driver available. We also decided to use the 2.8 inch display as this had the best fit in the new Simple model. We also decided to use the FT6206 touch screen although this can be easily exchanged as most touch screens are connected via I2C and the protocol is very simple to implement.

Adafruit has exactly this display as a break out board available. PJRC also sells the same display, but with a different touch controller. However, it’s not an issue to adept our code to another touch controller. And, of course there are display modules available at eBay. Just make sure your display has the ILI9341 display driver chip installed. Although our display system is very flexible you get best results if you choose a 320×240 pixel display to get quick results.

How displays work

Displays have a memory area and small pixels are connected to this memory (not in a circuit kind of way but you get the idea). When you change the bytes in that memory area the display reflects that. You modify this memory area using SPI to write data in specific memory regions. That takes time. And as the display immediately reflects any changes you can see the display building up the final user interface. Worst, you cannot just first fill a rectangle and then draw some text on it, as it would result in flickering. Animation is practically impossible although Paul did a very good job of making it as fast as possible.

There is a very easy way of fixing that: a back buffer. You store a memory area in your MCU that mimics that memory area of the display. You make changes there, you can overwrite data multiple times. And when everything is composed you send the whole area to the display. This does not allow for fast animations, too. But you get a nice, polished look and feel. But, Teensy does not have enough memory to store a back buffer!

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Xcode quick tip: Copy failed during export or uploading to App Store

I have been working quite some time on version 1.3 of Copper, our Mac EDA application. Check it out if you didn’t know yet. This version brings the ability to import your own STEP models of parts to create wonderful 3D models of your PCB. And this feature also added a lot of (partly external) code to my project.

After archiving the project I wanted to upload it to the App Store. So I went in the Organizer of Xcode, selected the newly created archive and clicked on “Upload to App Store”. But, export failed. I got a strange “Copy failed” error with a hint to some logs. Reading these logs is hard. As I added various Frameworks and external libraries to my application I thought it must have been something to do with that. So, for many months I tried again and again, I ripped my project apart but I never really got this issue solved.

Looking at the logs I noticed that it points out:

...
2016-11-16 09:53:45 +0000 652253 bytes for ./Contents/Resources/woodTexture2.jpg
2016-11-16 09:53:45 +0000 /usr/bin/ditto exited with 1
2016-11-16 09:53:46 +0000 [MT] Canceled distribution assistant

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Do I need a Logic Analyzer?

In one of my previous posts I tried to answer the question: “Do I need an Oscilloscope?“. The answer has been a short: Yes, under some circumstances.

But, there is another great measurement tool available: A Logic Analyzer. There are a lot of options, and a quick look at them reveals one thing: They are so much cheaper than oscilloscopes with the same amount of channels. The cheapest oscilloscope from Rigol, the 1054Z with 4 channels costs about $399 (but more if you add some options), the cheapest Logic Analyzer from Saleae costs $109. If you are interested in buying an oscilloscope, but don’t want to spend so much money at it (yet), is a Logic Analyzer an alternative?

Well, the good news is yes! Under some circumstances. Sometimes it’s even a better buy than an oscilloscope. Let me first explain what a Logic Analyzer does and why it’s so useful and often more useful than an oscilloscope.

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Little Helper

If you have read one of my previous blog posts about building a custom Teensy you already know I have been working on a device based on the Teensy design.

Working in my lab with electronics I came across different little challenges once in a while, and noticed that I am missing tools to handle them efficiently. Just a quick list, I am sure you could add various items to the list:

  • What is the I2C address of a chip? (yeah, you can work through the Datasheet but the Datasheets I know don’t have an outline topic for this. It’s somewhere hidden deep in text somewhere)
  • What is the voltage range of the analog sensor in my current environment (take a photo sensor)?
  • Generating PWM or DAC signals
  • Does this circuit do anything?
  • Does this circuit do anything specific?
  • Reading serial output of your Microcontroller/Arduino project

Of course these aren’t any issues that you could not handle with the tools you have. But each of these take time. Checking an IC for it’s I2C address is easy: Connect it to your Arduino Uno, firing up the I2C Scanner sketch and you are good to go. That is 10 minutes minimum finding your Uno, wiring it up, firing Arduino IDE, uploading the sketch. And everything while your workspace is full of components, wires and stuff for the actual project you are working on.

I had been working on wireless sensors for a while that should take the least amount of power possible. You cannot add status LEDs as they draw way too much power. I had those PCBs lying around and had no clue if they do anything. I had to carry my laptop around, connecting it to the PCB to read the serial port to see what it does.

Why, the heck did I learn all that programming and electronics stuff and not using it to solve that issue. I thought of a small, portable device featuring some ports to connect stuff like sensors and other circuits and some menu driven user interface to trigger various modules doing tests, reading data, you get it.

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Announcing Copper Beta

It all started with quite a complex PCB that I have been developing with Eagle CAD. A 4-Layer PCB with a lot of parts (>100) and quite a few ICs with a lot of pins. All these traces, all this pins and pads. There are so many possibilities to screw it up, that I always thought about this sentence all of you interested in this kind of stuff know well: “Hardware is hard”. It is.

And after triple checking every pin and trace, working through dozens of data sheets and controlling pin layouts I had it in front of me: My very own awesome PCB and hundreds of parts lying in front of me. I have a reflow oven and had to place parts on the board, prepared with solder paste. As you perhaps know, solder paste dries out after some time, so I had to be quick. I knew, that I had to place the 0.1uF capacitor on C1,C2,C3,C5,C6,… Searching for these parts on the boards silk screen drove me crazy. I had printed out assembly plans, etc. I had my MacBook running Eagle and started to search for each Part to get it selected in the board to know where to place it.

In these hours the idea of Copper took shape. At first, I only wanted a software that renders a simple representation of the PCB with a parts list. Select one or multiple parts and they are highlighted on the board. I fired up Xcode and a few days later I had it up and running. And it worked great. Whenever I discovered issues and shortcomings in Eagle CAD or my workflows and didn’t find a solution I added my own solution to “EagleCAD Viewer” (that’s been the name for quite some time).

Although I just did write this application for my own use, I invested quite some time to get rendering right, make the App look great and ironed out any bug I could find. Why? Because I just hate buggy, bad looking software, especially when it’s my own software.

A few months ago I decided to commercialize my Application and named it Copper. I think you will love it, and I really hope it will make your life easier. But before I sell this Application I must be sure it works great on all Mac OS X versions and with your PCBs. I don’t want you to buy into a beta test.

Update: Copper is available now for purchase (24,99 USD/Euro). There also is a free, fully functional Trial for Mac OS X 10.10+ available.

More Info and the Trial is available at our Copper product page.

Please report any questions to: support@copper-app.com.

Smarthub_Rev_1.8

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Building your own custom Teensy

UPDATE (November 24, 2016):

While this blog post still is very popular, it’s a bit old now. It still uses the old Teensy bootloader chip that is meanwhile deprecated and is not available anymore in larger quantities. However, I have been part of the dev team of the new Printrbot Simple 2016 and I have developed the display component which also uses the Teensy. Printrbot made everything open source.

If you are interested in building your own Teensy hardware, have a look in my Behind the scenes report and the Hardware explained report which makes the schematics and PCB available for download. This new PCB features the latest Teensy bootloader chip.

Although the bootloader chip is old that is described here, everything else like routing USB traces is not! Have fun reading it and let me know what you think!

UPDATE (December 15, 2015):

As you are reading this you might be interested in my custom built Teensy project named Little Helper. I made it Open Source under the MIT license including Schematics, Layout, BOM, 3D models of enclosing, and the complete Source Code. Have a look: Appfruits LittleHelper.

UPDATE (June 26, 2015):

Due to popular demand I have created a “reference board layout” and the schematics in EAGLE CAD (7.2) format. I created it by removing all components that were specific to my project. I just left in the Teensy part, the USB-port and a 3.3V regulator and rearranged the components so they fit in a small footprint. I have never produced the board but it should work (also it doesn’t do anything useful) as the components and layout have been working flawlessly in my own application.

This should speed up your development time for your own project. The board layout contains a switching regulator for the 3.3V which might be overkill if you are running your board of an USB-port as the provided regulator is mainly used with LIPO battery based projects and is hard to hand solder (I use a reflow oven which works quite well with QFNs). Use a simple LDO if you are just running your board with USB power. I have left the board layout for the switching regulator as it has been quite hard to get a good board layout with nearly no noise (switching regulators tend to be very noisy due to it’s nature) and should get you up and running quickly if you intent to do a LIPO-based project (of course you will need to add a LIPO charging circuit which can be found for example in Sparkfuns Power Cell product (see board and schematics for details).

All parts have an attribute named MPN for Manufacturer Part Number and MF for manufacturer. This way you can just use EAGLEs BOM-ULP script to export a BOM that you can directly upload to Mouser of DigiKey to get your parts.

Please note: Don’t order the MINI54TAN at DigiKey or Mouser. You will need to order the MINI54TAN at PJRC.com as this IC contains the core Teensy functionality!

You can find the EAGLE board layout and schematics in our Github repository: Custom Teensy 3.1 board layout and schematics. Please make sure to read this blog post before using parts or the whole “reference board” in your own project as there are quite a few things to consider which is largely documented and described below.


If you are reading my blog you might know that I really love Teensy. Teensy is an ARM powered very little Arduino compatible development board. It does one thing so damn good and I think that is very important for a development board and one of the keys to the success of Arduino: Easy programming. You do not need to connect wires and fancy boxes (JTAG programmers), just connect with USB and click on the program button.

But I am not a big fan of using development boards within final products. Although Teensy is really small it’s too high to pack two PCBs together. Using headers for easier soldering and it gets worse. If you really want to build small products you will often have to build your own PCB. Paul Stoffregen, the creator of Teensy enables these efforts by providing the bootloader MCU in his own store. They are very professionell. I had a few issues with german customs and they immediately sent out new ones and I received a refund for the first package that did not make it through.

Of course it’s not Pauls business model to help you out building your own Teensy, although he was very helpful in the forum. You will have to rely on the great Teensy community or blog posts like this one.

As I had a bit of trouble to get my custom Teensy board up and running I will try to give you some advice on how to build your own. (more…)

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Do I need an Oscilloscope?

If you are interested in Electronics, you will likely ask yourself sooner or later if you need an oscilloscope and especially what to buy if you have decided to do so. As I have been in the same situation a few months ago I likely know what’s going on in your head. Give me a minute to save you a few more sleepless nights thinking about this topic.

You can find a lot of infos about scopes. You will find hundreds of hours of video reviews of scopes, just look at the amazing EEVBlog. But non if these videos really gave me an answer to my question: Do I actually need a scope and what can I do with it.

Did you love playing with your dads HIFI-system and turning the knobs? Well, I know a scope is kind of a sexy tool with it’s knobs for you… But do you really need one? (more…)

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