Instructables

Step 2: MODIFYING THE INVERTER

Picture of MODIFYING THE INVERTER
10_step02_board_bottom_cut_traces.jpg
11_step02_board_top_modded.jpg
12_step02_board_bottom_modded.jpg
This step demonstrates how to modify the inverter so that it responds to an audio signal instead of sound waves. Before trying this mod you should see if an earbud placed over the inverter's microphone works well enough for your needs. My music player had to be unacceptably loud to get the inverter to respond to an earbud.

The T-qualizer inverter uses an electret microphone to sense sound and drives five lines connected to an EL panel made to look like a graphic equalizer. The number of lines it drives depends on the amplitude of the sound sensed. The inverter drives the lines additively which means if line three is being driven then lines two and one must also be driven. The first and last wires of the ribbon cable are both connected to common and the connector is not keyed, so it is possible to reverse the order in which the panel's colors light up.

A modded inverter has a couple of advantages. First, it allows the inverter to be triggered by a remote source via a headphone extension cable. Note that the audio source doesn't have to be outputting sound through a speaker for the inverter to work. Second, a custom waveform that steps its amplitude up or down can be used to precisely control which levels the inverter lights up. So you can use a specially-made audio file instead of music to animate the EL wire.

I've only worked with one of these inverters, so I can't say how likely you are to have one just like mine. I'm hoping that these modifications are generic enough that you will be able to apply them to a different inverter.  First I removed the screws holding the inverter's case together and inspected the circuit board. The sensitivity pot feeds power to the electret microphone's internal amp. The output of electret mic is then capacitively coupled to an inverting single transistor (M28S) amplifier. The output of the transistor is capacitively coupled to the EL driver IC. To make room for the audio cable I removed the barrel power socket. Mouseover the image notes to see the places on the board I'm describing.

Next I desoldered the electret microphone and cut the trace connecting the potentiometer (thumbwheel) to the IC's power pin. Doing this let me directly input an audio signal into the circuit. I had some success capacitively coupling an audio signal onto the microphone's output trace before making any modifications, but it didn't work quite right.

I found that the dynamics of the panel covered its full range nicely when the audio signal input was at a listening level that is slightly below normal. This means that if the volume was increased to a normal or loud listening level that the panel would be pinned to the red most of the time. Therefore I decided to reuse the potentiometer to attenuate the audio signal before it is input to the inverting transistor amplifier. To do this I cut the trace connecting the upper and middle legs of the pot and connected the left audio channel's wire to the upper leg and audio ground to the circuit board's ground. Now the thumbwheel allows control of the driver's dynamic range without having to change the listening volume of the music. My 2nd generation ipod shuffle has a noisy output, so it causes the lower level EL wires to light up even when music isn't playing. Using the thumbwheel to increase the input resistance fixes this problem.

Unfortunately, these modifications make the inverter susceptible to noise picked up by the audio cable. To fix this I used a 220 ohm resistor. I soldered the first leg to the audio line where it joins the thumbwheel and the second leg to where the negative battery terminal meets the PCB. Normally the barrel connector socket bridges the PCB's negative battery terminal pad to ground but since I removed it I used the remainder of the resistor's leg to connect them.
IYER936 months ago

Hi, I'm ishaan, a student in India. I too have the exac same invete PCB as you, so firstly thank you for doing this instructable, I've been wanting to mod my inverter for a long time, to read an audio signal rather than just hear.... sort of like wanting it to learn the language and the alphabets to make words rather than just have it interpret what is being heard, so thank you.

now one thing i'd like to ask u ... instead of going through the whole thing .... i'd like you to riddle me this ....

1.An auxiliary cable has a +VE , -VE and GND

2.An electret microphone too has a +VE cum SIGNAL pin and a -VE cum GND pin

A. if we were to combine the +VE and -VE signals from the aux and solder them in place of the +VE cum SIGNAL pin on the board and solder the GND wire fom the aux to the -ve cum GND pin

OR

B. if we were to connect the +VE signal from the aux to the +VE cum SIGNAL pin and combine the -VE signal and the GND from the aux and solder them in place of the -VE cum GND pin on the board

..... would any of the this work in terms of making the EL Wires dance to an audio signal ....

please advice before i mess up ... these PCB's are tough to get hold of ... and i only have two ... one that is the same as yours and the other is a smaller condensed version.... this is a mod I've been thinking of doing fo quite some time... as the battery management and power management is done.... except that the mic is a really stupid part ... in the sens its unable to pick up music if not close to the music and this hampers the visual appeal..... i'd like to mod it so i can make custom shutter that dance to music.

micleads.jpg