GROUP 4

Doron, Luciana (Luxz), Talita

This Technology research consists of two parts:

Freak out

The midterm project where we tried to produce images variations through sounds signals generated on the BX-24, programmed with the FreqOut command.


Video Signals

The research on video signal and its capability to generate images variations on different screens display.

1. What is a video signal?
2. What do they carry?
3. How are they displayed?
- Interlaced scanning technique


4. Measuring video signals: the Oscilloscope x Vectorscope

Freak Out

The FREAK-OUT code
(Exciting experience with analog sounds command on the BX24 and video)

Programming the chip to generate a sound is basically done with the command Call freqOut (pin, frequency 1, frequency 2, time interval)

The BX can modulate between only two frequencies. This at first seemed very limiting. Assigning a button to each freqOut pin to trigger a certain sound reminded us too much of the methodology and the flat, obviously digitally produced tones on a touchtone phone.

However, as soon as we realized that the frequencies and time intervals could be assigned variables to them well then it became a bit more interesting.

Approaching this in the conversion of the previous experiments, we proceeded to think of this as a basic digital input, analogue input and analogue output application of the BX.
click image for enlargement
Development: sequence one

So we wired the breadboard with three potentiometers: one for frequency 1, one for frequency 2, and one for the time interval. The digital input is a switch, which turns this loop on and off.

Now that we had everything connected and soldered, we are now ready to listen to the sounds produced and make further decisions more concerned with aesthetics (for output specifications, please see output sound section of this page).

The way that the BX simulates an analogue signal is by creating pulses that are too fast for the eye/ear to perceive. This is referred to as a pseudo-analogue signal. In reality, a square wave is always produced; with ons and offs happening so quickly that to the human perception it seems to be as smooth as a sine wave.

By adding small resistance fixed resistors to the potentiometers that controlled the frequencies1 and 2 I got (from the debug.print command) a smooth variation between 0 and 1023 (integer values). For the coarsness of the wave, or the time variable, we experimented with various different kinds of resistors. From the previous laboratory session with variable resistors we had noticed that the difference between the maximum resistance and minimum resistance decreased as the fixed resistor increased. When using a low resistance resistor the pulses went on one extreme at a very HIGH rate, producing a steady sound of duration of 2 secs, then a pause back from loop to do simulating an analogue, smooth signal of a short duration.

On the other extreme, the sounds would become very choppy, very digital with obvious ons and offs intercutting them. The pause between the end of a cycle and the start of the next one on the analogue-simulating end bothered us quite a bit.

It seems that the analogue-simulation was interrupted by the inevitable cycles that the microcontroller has to undergo and is therefore not a very good simulation. So we made our minds for a high resistor to ensure that the pulses would stay slow, enabling the sound to be faithful to its creator: p-u-r-e-d-i-g-i-t-a-l.

The second part of the BX sound generator setup was to add another channel to it. We did this by adding another switch that would trigger a second freQout command that had different parameters. Now we understood that the BX would output one freqOut command at once, so we were at the expectation of experimentation and seeing what resulted from this. We added a switch to another pin that when on would trigger a loop of modulating frequencies that were controlled by flex sensors. The time variable we left common with the first freqOut command, being controlled by the same potentiometer.

click image for enlargement click image for enlargement
Output sound

The output sound is done through a mini jack cable.
When reading the specs of the BX we discovered that the freqOut command output a mono signal. But of course when dealing with sound it is important to take into consideration the stereo nature of human hearing. So we needed to convert the mono signal into a double-mono left-and-right signal. We had a stereo headphone extension cable, which is basically a mini-jack cable with one stereo female end and one male stereo end. We cut the cable open and found that there were two power conductors (one for each channel), which had a shared ground. The two power conductor wires were soldered together and attached a lead to the end and repeated the process for the ground. Connecting this to the pin on the freqOut and connecting to this a SELF-AMPLIFIED pair of computer speakers gave us a double-mono sound output.

click image for enlargement

NEXT