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    Inspired by Music Tech Fest in Berlin, The Ben Heck team finishes work on the Intel Edison Laser Harp. Ben and Karen handle all the electromechanical work while Felix, the Linux guy, finishes the coding. Have you ever made an electronic music instrument? Let us know!

    Episode 253: Ben Heck’s Intel Edison Laser Harp Part 1: Design


    The Ben Heck team finishes work on the Intel Edison Laser Harp. Earlier, they got the Intel Edison working with SoundFont: a group of audio samples that can be played back by a MIDI. They also built the top half of the harp which had the laser emitters. They now go to work on the bottom half of the harp which has all the laser detectors and ensure that the 24 emitters on the top of the harp line up with the 24 detectors on the bottom.


    Ben and Karen handle all the electromechanical work while Felix continues working on the Intel Edison, the audio codec, an amplifier, and managing the voltages. He builds a 24 pin header with ground and a 3V plug for the lasers and 5 V plug for the detector and NOT gate. He also connects all the GPIO of the Intel Edison board to level shifters. The level shifters take 5V from the NOT gate and bring it down to 1.8V for the GPIO of the Intel Edison. The Intel Edison GPIO runs at 1.8V and if they supply more voltage than that they could burn out the pins.


    The way integrated circuits work is the output is set by the value they put into the integrated circuit supply. As a result, they cannot take 1.8 V from the Intel Edison and use that as voltage supply to do the level shifting. Also, the way level shifters work is if the voltage supply isn’t present the output will be whatever the value of the input is. The solution is to use LM 317, a popular voltage regulator.


    Felix connects the Intel GPIO to the level shifters and makes three headers for Ben to plug his circuitry into. He attaches two voltage regulators to a protoboard. They both have 5V as the input. One of them is the LM 317 that is going to set 5V down to 1.8 V and the other is the LM 3904 and that is going to set the 5V down to 3.3V. Felix wires up a “for sure” button test to ensure the IO works before connecting the harp.


    Ben uses a laser cutter to make the pieces for the receiver assembly inside the harp. The receivers are recessed so that indirect ambient light has less affect on them. He glues pieces together to make the basic frame and then inserts the photoreceivers and standoffs. Karen pokes holes in the frame and adds LED indicators to ensure each one of the lights is lined up. There’s an LED indicator for each sensor, so they can test alignment without the entire system running. Once the emitters and receivers are in sync and aligned they glue and screw the entire harp together.


    Ben wires up the voltage dividers on the light sensors on the cartridge and puts it in the harp. He wires all the photoresistors to four hex inverters for 24 total outputs. He then attaches these outputs to both the LEDs on the harp and then duplicates them into another ribbon cable which plugs into Felix’s Intel Edison board. The Intel Edison goes into a board that all the level shifters and audio drivers. A battery pack is attached to the Edison to keep it booted up while they test other things. The laser harp is attached to the board and the main unit is powered up. 5V goes to the driver board, 3.3 V goes to the laser emitters, and speakers are plugged in. The laser harp is fully assembled, tested, and working.