Oz 26/5/03

VooDoo Vibe Led Driver Documentation v1.0

After coming across this circuit about 3 years ago I vowed that I would build it! I know it's taken a while but all those cool sounding dist pedals get in the way.
I am working on the Audio part as well, but don't hold your breath!

After getting so much from our online community, I thought it was time to give something back!!!!

I have connected a veroboard version of this to drive the LEDS in an Easyvibe, and to be honest with you this takes a bit to get a good sound out of, not like the one knob of the Easyvibe, but hey we're DIY'ers and why use one knob when you can use 5!!

I figured this could be used for anything that uses LDR's as controllers, like phasers/tremelos etc.

I have traced and checked this PCB design out so it should work straight out of the box

Here is some info from the RM site detailing the function of each control.

Range :
Selects either a sine or triangular waveform, with three speed ranges for each. 

Speed :
First set by the Range control giving three sine waves and three triangle wave speed ranges: slow, medium and fast. The precise speed is then adjusted by the Fine control. 

Bias :
Affects the dc level of the LFO waveform; in other words, the brightness of the LEDs at the midpoint of a cycle. This changes the centre frequency of the phase-shifting network. The Bias Knob acts as a filter tuner and is used to dial in sweet spots to achieve different tonal colors. Bias is most effective in the chorus mode and enables the filter to be 	centred on different frequencies, emphasising either the bass or treble frequencies within the sweep.

Symmetry :
Basically controls the modulation so that the effect sounds as if it is speeding up at one end or the other of its sweep range. Symmetry controls the ratio of the rise time to the fall time of the modulation signal being used. For example when using slower speeds you can make the sound build up slowly and cut off quickly creating a helicopter type "woof-woof-woof" sound. The waveform can be adjusted from fast attack and slow decay, through perfectly symmetrical to slow attack and fast decay. 

Intensity :
Sets the level/amount of effect

Construction Notes :

The pcb was designed using Express PCB (it's free and easy so if you ain't got it, get it), I have included the data files.

The 8038CCPD is available from Farnell.

Moving from left to right through the schematic:

Point 'Y' is the take off point for connecting an external speed controller, (Roland FV5????). 

Points 'X' are the return from the external controller, as shown on the schematic use a short circuiting socket or just use a link between the 'X' pads if you're not going to use external speed control.

VR1 and VR2 are 5k trimmers that set the upper and lower limits of the external control.

VR3, VR4, VR5 and VR6 are panel mounted linear pots.

Pads marked A & A1..6 and B & B1..6 are halves of a 2pole, 6 position rotary switch with the A pads being one pole and the B pads being another, consult the schematic when wiring it up.

You may notice that the PCB has a resistor marked R15a, this is 330k. This resistor is not on the drawing. One of the problems in getting this working properly was found when I realised that IC3pin2 did not have a bias voltage, and therefore any changes to the input of pin2 made no difference to the pin1 output.

I have also added an extra 150 ohm resistor (r26) and LED on the output to act as a visual indicator of what the circuit is doing. I don't know how many more LED's it can drive, maybe someone else can tell us?

The black stripe on the PCB design is a 1inch line to aid in the sizing of the PCB when you print it, you will have to check the orientation of your printout as to whether it is track side or component side, I make my PCB's using the Flouro light method on clear film so it's easy for me, the 'press'n'peel'ers amongst you may have to mirror it in your graphics program!.

I hope that I have covered everything...