What do you do when you want to rock out on your keytar without the constraints of cables and wires? You make your own wireless keytar of course! In order to get the job done, [kr1st0f] built a logic translator circuit. This allows him to transmit MIDI signals directly from a MIDI keyboard to a remote system using XBEE.
[kr1st0f] started with a MIDI keyboard that had the old style MIDI interface with a 5 pin DIN connector. Many new keyboards only have a USB interface, and that would have complicated things. The main circuit uses an optoisolator and a logic converter to get the job done. The MIDI signals are converted from the standard 5V logic to 3.3V in order to work with the XBEE.
The XBEE itself also needed to be configured in order for this circuit to work properly. MIDI signals operate at a rate of 31,250 bits per second. The XBEE, on the other hand, works by default at 9,600 bps. [kr1st0f] first had to reconfigure the XBEE to run at the MIDI bit rate. He did this by connecting to the XBEE over a Serial interface and using a series of AT commands. He also had to configure proper ID numbers into the XBEE modules. When all is said and done, his new transmitter circuit can transmit the MIDI signals wirelessly to a receiver circuit which is hooked up to a computer.
If you’re like us, you probably have a box (or more) of wall warts lurking in a closet or on a shelf somewhere. Depending on how long you’ve been collecting cell phones, that box is likely overflowing with 5V chargers: all with different connectors. Bring them back to life by doing what [Martin Melchior] did: chop off the ends and solder on a bunch of USB jacks.
You’ll want to use chargers rated for at least 500mA (if not 1A) for this project, or you may be wasting your time considering how much current devices pull these days. Get your polarity right, solder on a USB jack, and you’re finished. Sure, it’s a no-brainer kind of project, but it can clean out some of your closet and give you a charging station for every room of your home and the office. [Martin] glued the USB jack directly onto the adapters, so there are no tangled cords to worry about. iPhone users will need to do the usual kungfu if you want your Apple device to charge.
So the Raspberry Pi sometimes doesn’t have the juice needed to run power-hungry USB dongles. The most common issue is with WiFi adapters. The solution has long been to use a powered USB hub, but [Mike Worth] didn’t want to take up that much extra space. The solution he worked out injects power directly into the dongle itself.
The red and white wires coming out of the side provide the 5V source. This is coming from the same USB mains power adapter that supplies the RPi board itself. To connect the wires to the dongle he made an adapter out of some strip board and the shielding from the dongle. The end of the strip board pokes out of the shielding far enough for him to solder on some wire, which is then soldered to the traces on the dongle’s PCB.
You can just plug this in and get down to business. But while he was at it [Mike] added an improvised antenna for better reception. It’s the same type of hack we saw him use for a Bluetooth dongle in this links post.