Finished Pieces

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.

    Light Synth:

    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.

    The Benjolin:

    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.

    Input adjustment
    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.


    15 Responses to “Benjolin Light Synth”

    • 1

      circuitben said:
      February 17th, 2010 at 8:27pm #


      I won’t ask any questions, because there would be too many of them. Just well done – and thanks.

    • 2

      casper said:
      February 17th, 2010 at 11:35pm #

      @circuitben. Thanks! I still have to write text for this page. Hopefully it will answer some of your questions. This is one of the few pieces I’ve made that’s just for me!:) So it’s a lot more complicated than most of the stuff I make.

    • 3

      Anthony Liekens said:
      February 18th, 2010 at 9:08am #

      Beautiful. Unlike many other random sound generating synths, this can even be listened to and possibly be enjoyed by a wider audience. Your project pushes me to give a higher priority to making a synth again …

    • 4

      Oliver said:
      February 21st, 2010 at 8:39am #

      Really cool!
      I like the light ball! Will there be schematics of that to?
      Big up

    • 5

      casper said:
      February 22nd, 2010 at 12:06am #

      I posted some info on the LEDs above. No schematics yet, but there’s enough info there to get you started.

    • 6

      Clarke said:
      April 1st, 2010 at 11:24am #

      Amazing, mesmerizing unit/performance. Nice job!

    • 7

      Richie Zxy said:
      April 6th, 2010 at 8:10pm #

      wow; simply amazing. Most inspiring work, sir. Laying out your path of approach,, very grateful. please, keep it up.

    • 8

      Wyatt said:
      April 11th, 2010 at 11:38am #

      Cant wait to build one of these at Bent, does the one were doing have the light orb as well or just the Benjolin circuit?

    • 9

      casper said:
      April 11th, 2010 at 12:12pm #

      @Wyatt: The one at Bent is just the Benjolin, but I’ll talk about how to mod it further. Have you reserved a spot yet? There’s only 10 spots and I expect it to fill up fast.

    • 10

      Wyatt said:
      April 14th, 2010 at 7:08pm #

      Thanks for the tip, I just reserved.

    • 11

      max abeles said:
      April 23rd, 2010 at 1:36am #

      hey there this is cool!
      I have a quick question..When ever I try connecting lights to my 555 timer synths (using similar circuit, but tip120 not 122) the sound changes. Is this normal?
      Max (we met a while back at handmade music 3rd ward, i had tv linked to 555 x 2 timer synth etc.)

    • 12

      casper said:
      May 2nd, 2010 at 12:48am #

      @max: hey! good to hear from you.
      what kind of LEDs and power supply are you using? it may be that the strain on the supply is messing with the 555/audio. I used a separate power for the lights. They each pull 350mA so that’s around an amp of rapidly fluctuating pull. that’s enough to mess with the sound if they were on the same supply. You could also try just powering the LEDs off a separate regulator. or getting a supply with a greater current rating.

    • 13

      Ben Wood said:
      October 15th, 2010 at 5:08pm #

      Will the Banjolin be available for sale at all? O’r maybe a plug in pulsing light to be used with the drone lab ? You’ve inspired me greatly over this last year, thank you.

    • 14

      Mr James said:
      April 12th, 2011 at 11:57am #

      Hello Casper electronics!
      I have been searching the net for weeks looking for a cv mod for delay pedals (especially the EHX Memory man)
      Would you be so kind as to post a pic on how its done? After playing with the Drone Lab for a while, I’ve started experimenting with its CV possibility’s. It has hit me hard, and I now want to CV sync everything. I have even been dreaming in CV! Any advice on making CV in/out’s for Bent Toys and effects pedals, would really help get some projects flying. Thank you

    • 15

      casper said:
      April 24th, 2011 at 12:41am #

      Hey! I’ve got the cv bug too. I did an article for make magazinethat shows how to trigger toys and pedals with cv. Just did a memory tap tempo clock input mod that would work great with the drone lab. I’ll try to get that up soon.

    Leave a Reply

    If you're not already logged in, there might be a question you need to answer before you post to prove you're human. It's there to help stop comment spam.