While Robert’s working on the LED controller board / signal processor / micro SC card holder / voltage reference board (yep, definitely multifunctional), it’s my job to see which cell phones will communicate with the Teensy-based Photosynq via the standard USB connection.
Answer: Not many.
Here’s the problem in a nutshell: For two things to talk with each other via USB, one must be a “host” and the other the “slave”. The host is the one in control of the conversation. For example, your PC is a host and your mouse is the the slave. So to connect a Teensy microcontroller to your phone, your phone has to be the host. Android operating system has allowed your phone to act as a host since version 3.1 using a special USB OTG (On The Go) cable, but many (dare I say most) equipment manufacturers are not creating phones which work with this standard. For example, a Nexus 4 does not communicate via Serial with our Teensy (at least not without a lot of fooling around), but a Toshiba Excite tablet does. There’s a big list here of what is and what is not USB host compatible.
I was impressed with the variety of Android Apps available for those devices which do work when you have the right device. I found 3 great apps which allow you to send and receive data via the Serial port to the Teensy (just like the standard Arduino IDE Serial Monitor): USB Serial Monitor Lite, UsbTerminal, Slick Labs (regular and pro). All worked very well with some minor differences and little glitches, but overall I was impressed – too bad so few devices are USB Host compatible.
In addition, only a portion of those OTG compatible devices actually supply the full 500mA power (as per USB 2.0 standards) to the USB device. This is a problem for us, considering we would like to have small bursts of potentially significant current to run the LEDs.
So, my dreams of a simple, universal, plug-and-play device appear shattered!
No matter – it’s time to look into Bluetooth and wireless options (like Eye-Fi and/or Sparkfun’s bluetooth module) and add a battery. Hope to get them in in the next few days and test them out. More updates then!