Electrical – Teensy as USB host

The cheapest way? Use a µC with USB built in. Many of the pic18 and upwards have this. So do many other makes of µC.

The simplest way? As you already state - convert it to RS-232 at TTL levels with some form of conversion chip like the FTDI.

Yes, there could well be problems with drivers for both solutions, but it is more likely the FTDI will be supported out of the box. However, the first solution has the advantage that you can make the µC look like whatever device you want it to look like.

Oh, and as an aside - some of the high end PICs (eg some pic32 chips) have USB host built in as well. Just thought I'd mention it...

I did not figure out how to do it from teensyduino (aside from having it also be recognized as storage in addition to keyboard). But I did find out that if you skip the teensyduino and just edit C files and compile them, then manually load the hex file to the board it work just fine as a keyboard on android and PC.

Here is the page I used most to get it set up: http://www.pjrc.com/teensy/usb_keyboard.html

I'd still be very interested if any one knows how it can be set up so that it will work from teensyduino.