Introduction: Goblet Drum Two Channel Sound to Light Circuit
This fun project came about when sound analysing my doumbek goblet drum tonal characteristics.
It became apparent that reliable frequencies could be chosen for the high and low sounds of the drum and filter calculations performed accordingly.
A supply voltage of 18VDC was chosen for the following reasons:
1) Ubiquitous availability of the PP3 battery.
2) The common requirement of 12VDC operation for LED strip lights.
This project is aimed at the competent hobbyist/engineer experimenter. :)
Check out the video for easy 'nuts and bolts' illustration. Enjoy! https://youtu.be/acg4jc02VnI
Step 1: Determine Your Goblet Drum Tones
Using a sound analyser (free app for smartphone) determine the tonal frequency of your low and high percussion sounds.
If your drum sound characteristics fall within the scope of the circuit calculated filter values shown, then
no further consideration is required. If your drum characteristics are tuned quite differently you might need recalculate your filter frequencies accordingly. It should be possible to optimise this by adjusting the multi-turn trimmer pots in each filter stage to new calculations using the online filter design tool:
Step 2: Build the Circuit
Build and test the circuit using a sine wave tone generator and LED brightness (or oscilloscope).
I used a smartphone app to generate the required tones. Direct connection via headphone socket to circuit is preferable.
!! UPDATE !!
I have since found that tuning the low frequency 'doum' filter 5Hz down from the original instruction improves close quarter playing, e.g. if sat on a sofa it's proximity lowers the bass tone of the drum reducing or stopping LED output. New range is now 110Hz to 120Hz instead of 115Hz to 125Hz.
!! UPDATE Sept 2019 !!
Schematic diagram now updated due to component value changes.
More details and a new playing demo on my channel:
https://www.youtube.com/channel/UCCpnL49oNVs0Wp0fD87uBeQ
Step 3: Assemble the Circuit Into the Drum
If your build appears to be working (using sweep tone assessments) then fit your project into the goblet drum.
You will need to have suitable fixtures in place for the two channels of LEDs, microphone, circuit board, batteries and on/off switch. I used velcro strips (and pillar standoffs)* for the veroboard assembly / batteries and switch.
For the long LED strip it was necessary to glue it securely. The microphone is glued in place atop a loop of duct tape for suitable mechanical decoupling from the drum body.
*It should also be possible to assemble the veroboard electronics into a low profile ABS box and use velcro strips on the corners, to the inside of the drum. Access to the trimmer pots is required to allow post assembly tweaking for playing styles once the goblet drum is operational again.
