ELEVATOR MUSIC BOX > technical construction > notes
1. TWEAKING THE ALTIMETER.
Out of the box, the altimeter was not very accurate for our purposes and didn't really register much of a change that was useful in the elevator. The advise of Marko Tandefelt and his persistence that basically you can do anything and make anything work, led us through many an hour up and down in the elevator mostly trying to calibrate the two 1M ohm trimmers for the right ADC Ref and low end op amp settings. Eventually we got it down to within an accuracy of one foot!
| . |
- The first op amp circuit was designed to use a trimmer to push down the tiny varying voltage which was hanging at around 2.5-2.6 volts to near zero, so that the lowest voltage would be almost zero volts, and the highest reading, 9 floors up, turned out to be be, consequently, just a bit higher - around 0.05. - The second stage was an amplifier with a gain set by a trimmer to increase the voltage range, thus allowing a detection in voltage change as often as every foot |
2. LCD SCREEN
While the LCD screen may seem unneeded for the end product, it is crucial for calibrating, in order to watch the voltage rise and fall when riding up and down the elevator in test mode. Also because the voltage ranges correspond to the floors, and the speed of every elevator is somewhat different, there is need to know what the voltage reading is for each floor in order to program the corresponding ranges of criteria into the code.
3. AUDIO OUT
Most small devices like the Rio mp3 player or CD players, etc. do not have enough amperage to play the music loud enough so it is necessary to amplify and use nice speakers to maintain the integrity of the musical sound design. The elevator box uses a 13.2 V 18 watt amp for two 4 ohms Bose speakers manufactured by Apple Computers. The mp3 Player connects to the amp through a stereo 1/8" mini plug on one end and a soldered breadboard connection on the other to the amp kit and then proceeds onwards with low resistance monster speaker wire from the amp to the speakers.
4. BATTERIES
The stamp gets its own rechargeable 9V nickel metal hydrade battery, the mp3 player gets its own 1.5 AA nickel metal hydrade battery and the audio amp, which needs the most juice, gets a 7.2V/2000mAh Ni-Cd Battery Pack. A battery solution at this point is poor because even the most high end, compact batteries at full operation last only a couple of hours at the most.