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By Oleg Mazurov  USB Host Shield prototypes 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.
Oleg.
By Oleg Mazurov  USB Host Shield prototypes 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.
Continue reading Arduino USB Host Shield build log. Part 2.
By Oleg Mazurov  5V to 3.3V converter
Parts has arrived yesterday and I started test-building my USB Host Shield prototype PCB to check functionality and buildability. Since design is not final, I’m not publishing Eagle files yet – they will be online as soon as I get all errors fixed. In the meantime, the PDF of the schematic diagram is available.
One of the goals of this design is to make it compatible with both 5V and 3.3V Arduinos. Since MAX3421E is 3.3V part, I added some extra circuitry to provide 5V compatibility.
I started my testing by building 5V to 3.3V converter piece to check parts values and circuit layout. The circuit is located in the upper-left corner of the schematic and in the lower-right corner of the board. Please also take a look at the title picture if you haven’t already to see the layout. This converter comes in handy if, for example, you are using 5V Arduino and/or need to provide Vbus power for bus-powered peripheral and want to use this supply to power the shield/Arduino also. Converter is rated for 600ma, enough to power both MAX3421E and Arduino, if necessary.
Continue reading Arduino USB Host Shield build log. Part 1.
By Oleg Mazurov  Arduino USB Host Shield PCB
While developing Arduino code for MAX3421E USB Host controller I was thinking about making a shield for it. Sure, breakout board riding on top of protoshield works just fine, however, some people don’t like the wire clutter. Additionally, since many Arduinos are 5V devices, level translation may be necessary. I was playing with different configurations, and routed a draft prototype to build and see how it would look like. I received PCBs today from BatchPCB – just in time before the weekend.
In addition to MAX3421E with accompanying parts, the shield contains level translating logic for all signals and GPIN/GPOUT ports, and 3.3V to 5V step-up and 5V to 3.3V step-down converters. I decided to use DIP packages for level translators – this way if translation is not necessary, the PCB can be simply modified with jumper wires.
I’m going to start building/debugging this board today and produce final version in 2-3 weeks. After that, the plan is to order a batch of boards, build them and send to beta testers. If you want to participate in testing, leave a comment and I’ll put you on a list.
Oleg.
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