Benjolin Light Synth
This piece is a complex audio and light pattern generator. It is capable of creating dense sound scape, intricate melodies and pulsing rhythmic sequences.
The light display utilizes 3 high intensity LEDs in red, green and blue. Combining these three colors allows for full spectrum color mixing. Signals taken from the audio circuitry are used to control the 3 LEDs independently. The lights can be configured in a variety of ways to respond to the circuitry. In some cases the relationship between what you hear and what you see will be very obvious, in others it will be less obvious or not at all. Regardless, the sound and light will always be coming form the same circuitry and are linked on some level. I find the varying degrees of connection to be one of the most intriguing aspects of the color display. See the videos below for examples.
At the heart of the instrument are 2 Benjolin circuits . You can see the 2 benjolin circuit boards in the photo below. What’s really exceptional about this circuit is the breadth of sounds and effects that can be generated. It’s impossible in one sitting to explore all of it’s potential. I’ve left this on for the last 2 weeks and have found it to be consistently entertaining.
LED display design:
The light circuit is really simple. I just used a power transistor and 2 resistors for each color.
The transistor I used is model # TIP122. I think most any high power transistor will work.
Choosing your LEDs
I used 1Watt LEDs for this piece. These LEDs are great to work with because they are extremely bright and put off a lot of light. A few things to be aware of when using high power LEDs:
—They HAVE to be on a heat sink or they will burn out in a few seconds. I used a 2″x2″x.25″ chunk of aluminum for my heat sink. You can attach the LEDs to the heat sink with heat conductive tape or you can bolt it down. If you bolt it, make sure you don’t short the contacts of the LED to the heat sink. Use plastic bolts or plastic washers to isolate your LED.
—These LEDs pull a lot of power. Make sure you are using a power supply rated to handle the load of the LEDs. It’s always best to over design. If it needs 700mA use a 1amp supply.
—Protect your eyes. 1Watt and higher LEDs can damage your eyes if you look directly at them for extended periods….really… they’re bright! so be careful and use a diffuser of some kind.
I’m using three 1Watt LEDs in RED, GREEN and BLUE. You can use a single tricolor led instead. I tried that and it works fine. Expect to spend $4-$10 a piece for these LEDs. I’ve had some luck buying them cheaper on ebay, but your better off getting decent quality ones at a pro shop like Mouser.
They want to be driven with 350mA to achieve max brightness. The 4.7ohm resistor (collector to cathode resistor) is what is setting the current. This value will change if you use a different power supply. The value will go up if you use a higher voltage supply. I used a mA meter to test the amperage draw of the LED with different limiter resistor values until I got a pull of around 300mA.
The driver circuit
The driver is what powers your LED. In this case I’m just using a transistor and a 5volt DC power supply to do this. The transistor is wired EMITTER to ground, COLLECTOR through a 4.7ohm resistor to the LED cathode (the – terminal), BASE through 10k resistor to the control input.
Choosing a power supply
The resistor values given above assumes that you are using a 5VDC supply. If you use a wall wart, make sure to test the output. More likely than not it is a few volts higher than marked. If it is, you will want to raise the value of your collector to cathode resistor. Test the current pull of the LED until you get around 300mA. To drive 3 LEDs you will want a supply rated at at least 1.5Amps (1500mA).
I chose to make my own supply for this project. I used a 6volt 1.5amp transformer. I used an LM7805 regulator to get a steady 5VDC supply. The regulator will get HOT so make sure to use a big heat sink. Building your own supply is fairly easy but there are some inherent dangers whenever you work with line level AC. If you’ve never built a power supply before, look up instructions and read about it.
I also added channel adjustments for each color/input. It’s a cool feature but not crucial. They’re not perfectly configured, but they work. The problem is that the brightness sweep is uneven, it drops suddenly then very slowly as you turn the control down. I’m sure by changing some values around I could get a more even sweep. It works well enough for now.
The input jack is wired to the right lug of a 100k pot. The left lug goes to ground through a 10k resistor It’s powered with a 5VDC 1.5amp supply. The three LEDs combined pull about an amp, so make sure you use a power supply rated at 1.5-2amps+. ALSO test the output of the supply you use. If it outputs more than 5 volts, you will have to adjust the 4.7ohm resistor. I’ll try to get a schematic up soon.
Click on the green arrows in the music player below to hear some samples.