This is the status update on Arduino USB Host Mini development, announced 3 weeks ago. I received rev.0 PCBs last Saturday – BatchPCB is faster than ever! I made a test build (see title picture) and after fixing one major and several minor mistakes placed an order for what I’m hoping will be the final pre-production sample.
The prototype was built to sit on top of Arduino Pro Mini to make access to the parts easier during troubleshooting. On the final board USB connector is placed slightly further away from the pins; it will be possible to place Arduino on top of the shield so that the height of the “sandwich” will be less or equal to the height of USB connector.
In 2-3 weeks I’m hoping to finalize the design and start producing the USB Host Mini. Stay tuned!
Many people asked me to post a video showing an arm from inverse kinematics article in action. While making a video, I realized that shots of the arm following a pattern of computer-generated coordinates is going to be less than exciting and decided to add manual control. The video below shows the result. In addition to the video, a HID introductory page has been written describing HID communication basics as well as some simple Arduino code. Enjoy! ( Youtube link, where HD quality video can be selected ).
This post announces starting of development of new Arduino USB Host Shield variant. There are several projects in the works (thanks, guys for letting me know!), where standard size Arduino board is too big. Since electronics of USB Host Shield is pretty simple, it was decided to shrink the board as much as possible. Here is the first iteration.
The initial revision of USB Host Shield in Mini form factor is shown on title picture, It is intended to be used with Sparkfun’s 3.3V Arduino Pro Mini. Intended applications include digital camera control devices, robots, as well as any other projects where size and weight has to be minimized. The Gerbers was sent to BatchPCB; I’m expecting boards back in couple of weeks. The main goals of this first prototype are manufacturability check as well as checking claims made below.
The Mini Host is simplified version of full-sized shield; only USB and GPIO are available. By default, VBUS is routed to VCC, therefore only self-powered USB devices are expected to function (even though I have at least one USB flash drive which works fine powered from 3.3V VBUS). I also provided extra pads to simplify signal re-routing, however, since there was no place left for jumpers a trace has to be cut instead. The same has been arranged for VBUS – if 5V power is necessary, Arduino Pro Mini/Shield combination can be powered with 5V on RAW pin, the VCC trace cut off VBUS and RAW and VBUS connected.
As soon as first prototype is tested, I will post CAD files and also make boards available at BatchPCB. Stay tuned!
Based on some discussion on the Arduino Forum, Richard has added this blog entry as work in progress on developing a library to support FTDI Serial port devices on the USB Host Shield. While cautious to publish at this early testing stage, the content here should help parallel developers.
My thoughts last year were that an FT232 driver for the Host Shield was not really useful. It seemed rather reverse to add a USB host plus a USB device to achieve something that can be done with a piece of wire. However USB is coming to be the baseline interface and is now the only interface offered on many serial devices.
USB Shield Hardware
Since my last blog update, Sparkfun have released their own version of the USB Host Shield. Great to have another source of the shield, with good stock at many International Sparkfun distributors. However they did add a couple of problems too:
Sparkfun swapped the RESET and the GPX pins from the original from Oleg. This means the shield will not work with the libraries from Oleg without a modification.
The current Max3421e_constants.h from Oleg has:
/* Arduino pin definitions for USB Host Shield signals. They can be changed here or while calling constructor */
#define MAX_SS 10
#define MAX_INT 9
//#define MAX_GPX 8
#define MAX_RESET 7
These work for the shield from Oleg, and existing published code and libraries without change.
However for the Sparkfun Shield they must be changed in Max3421e_constants.h, or optionally changed when the constructor is called to:
Blue Arduino USB Host Shield tied to telephoto lens mount
Developer Si Li shared his version of PTPDevinfo.pde, which fits into older Aduinos. Si wanted to get PTP device information from Canon EOS 500D, but he only has 16K Seeduino at hand. So he stripped devinfoparser off all unnecessary strings leaving only ones essential for parsing Canon EOS camera device info.
Making electronic devices requires close interaction with parts – reversing supply polarity, overloading inputs, and inadvertently shorting pins with test leads. Consequently, occasional destroying of parts is natural and shall be anticipated. I have been in correspondence with several electronics enthusiasts helping them getting their shields fixed and since their problems look similar to what I see when doing post-manufacturing quality control I decided to share my testing procedure along with some pictures.
In the past, it was customary to include schematic with every electronic device documentation. Complex devices, such as oscilloscopes, spectrum analyzers and other test instruments used to have service manuals containing detailed calibration and repair procedures. At some point, service manuals and schematics disappeared from the documentation for various reasons – equipment users were left to deal with manufacturer’s support or rely on their own reverse engineering skills. With open source movement and general understanding that sharing information is beneficial, manufacturers resumed publishing schematic diagrams of their creations. This article presents next logical step – a service manual for Arduino USB Host Shield, sort of.
Much of the testing is performed using board test sketch, available from examples section on github. Two files are necessary – board_test.pde and board_test.h containing diagnostic messages. The sketch tests 4 major parts of the circuit – SPI interface, general purpose input/output pins (GPIO), quartz crystal oscillator, and finally USB SIE. The main loop is written so that any test can be turned off if necessary by commenting out a single line. GPIO lines are checked using a loopback adapter – a thing that connects GPIN0 to GPOUT0, GPIN1 to GPOUT1, and so on. This test is made optional – if you don’t connect GPIO lines as described, the test will print an error message and continue with the next test. Also, GPIO test is placed between short and long SPI tests. The reason for this is that due to MAX3421E internal organization both short SPI test (reading REVISION register) and GPIO read/write doesn’t require working crystal oscillator, whereas long SPI test (reading/writing any other register) will fail and stop if crystal is defective. Therefore, when I see short SPI and GPIO tests passed and long SPI test fail I know that it’s actually a crystal which is dead, not SPI.
In addition to board test program, you will need a multimeter with thin sharp test leads to measure voltage and resistance between board elements. Some of them are quite small so a magnifier is also handy. Certain steps of the test procedure call for time-base instrument. Modern digital mixed-signal oscilloscope is the best choice, however, since very few people can afford one, a method of visualizing SPI traffic with plain analog oscilloscope will also be demonstrated. Logic analyzer is handy, but optional. For testing USB transactions you will also need some sort of device connected to shield’s USB connector. I usually use USB flash drive as a test device.
The article as well as board test program is written for worst-case scenario, i.e., shield which was built from scratch or came from major rework like MAX3421E replacement due to applying 5 volts to 3.3V pin. The test program works the same way with all four configurations, however, manual tests are shown only for “Simple” configuration, i.e. one with level translators and receiving both 3.3V and 5V from Arduino Duemilanove or similar (no DC-DC converters). Testing other configurations is slightly different and will be noted in the text. Also, “Minimal” configuration calls for specific type of test device – I use digital camera.
I’ve been working lately on improving manufacturability of my products. As a first result, I’m changing board revision of USB Host Shield to 1.21. The main difference between revisions 1.0 and 1.21 is level converters and jumpers in SMT packages. Picture on the right shows the very first panel of rev.1.21 board fresh from the oven.
Functionally, the board is the same. However, schematic has changed a little in part where control signals go through level converters. Therefore, it is important to use the right schematic when troubleshooting or hacking the shield. Downloads section has been rearranged and documentation for both variants added and labeled. I also posted closeup pictures of new board in store listings for the shield and bare PCB. I still have several rev1.0 boards available, they should be all gone by the end of the week so when you buy a board this week, you may get an old version. If you have a preference, let me know.
Lastly, from now on USB Host Shields comes bundled with stackable headers, the famous 4uconn part numbers 18688 and 18689. “Bundled” here means that by default they come in a bag, un-soldered. However, if you prefer, I can solder them for you – send me an e-mail after the purchase stating that you’d like your headers soldered and indicate the direction, female or male side up.
Release candidate 1 boards has been received, built, tested, and came out green wire free – at last! I placed an order for a small batch with board house and expect PCBs to be available in a couple of weeks. I am making second call for beta testers – if you write code and/or blog, drop me a line with a link to your blog and your voltage preference for the shield – 3.3V or 5V. I have more 3.3V boards left from prototyping so naturally people requesting 3.3V boards will have more chances to get one.
Updated Eagle and Gerbers are available in Downloads section. If you don’t have Eagle, here is the PDF of the schematic. Please make sure you are not using scematic posted in one of the previous articles – there are quite a few changes.
In this article I want to give an overview of the board and it’s features. I’d like to start with most complicated part, which is power configuration. First of all, the USB core part of the shield (MAX3421E) requires 3.3V to function. Second, bus-powered USB peripheral requires 5V on Vbus. However, to use self-powered USB peripheral we only need to connect 3.3V to Vbus to be able to see speed-setting pullup resistors. Consequently, for digital camera control applications, shield can be mated with 3.3V Arduino (like Sparkfun’s Arduino Pro) with no additional power supplies.
Making functional 5V version of a shield proved to be difficult. I was hoping to publish a release after building previous protos. However, it turned out that together with fixing old errors I managed to make several new ones and also missed a couple from previous prototyping cycle. So, in order to produce a proto containing less errors than a previous one, I spent a great amount of time checking everything I could think about, writing test code, running those tests against prototypes, and then repeating them on all possible mixes of available Arduinos and voltages.
Also, I found that USB-B connector on Duemilanove shorts GPIN contacts on a shield. Cover top of the connector with piece of Scotch tape, if you haven’t already.
Today I placed an order with BatchPCB to what I call “Release candidate 1″. I am hoping this is a design which will be released when I get it back in 3 weeks or earlier( BatchPCB is getting faster ). Also, I forked previous repo containing Arduino libraries, the current development is now contained in USB_Host_Shield. I removed Vbus power control support since it’s not implemented on a shield and added functions for GPIO pins read/write. I’m freezing previous repository to support old sketches.
While waiting for PCBs I will continue working on HID code for the shield and also write a library to control LCD/buttons via GPIO pins. Stay tuned.
I finished building Arduino USB Host Shield prototypes. Functionality has been tested, errors found, fixed, and 1.0rc boards ordered. Title picture shows two prototypes, 3.3V sitting on top of Arduino Pro from Sparkfun and 5V on top of Duemilanove (bought at Sparkfun also).
As you can see, the biggest amount of errors has been made in 5V part of the circuit. To be honest, I’m not quite sure all of them are fixed. At some point I decided to stop messing with temporary fixes and order a board – if anything is still not right, I will find out later.
One of the goals of this build was to test 3.3V to 5V DC-DC converter (schematic). You can see it populated on 3.3V shield. It can be used on 3.3V-only systems to provide power to Vbus. This converter is designed around LTC3426, delivers ~700mA (slightly more than needed for powering Vbus) and runs cold with 90-94% efficiency. Output ripple was measured at 25mV. Note of caution: you should expect stability issues when powering such setup from USB (for example, during development) – in one of my tests Arduino was regularly rebooting during USB drive connect.
