Kevin Melotti
John George
Frank Sandner
Voltage Regulator - Logic Chip - Load (LED)
The voltage regulator provides a constant output voltage of 5V independent of its input voltage. We used a DC power supply to feed the voltage regulator. Its input voltage can vary between 6.7V and 35V. With this established power supply we fed a NOR gate (DM47LS02) (Vcc). Due to the maximum input current of 8mA stated in the data sheet, we used a pull-up resistor to limit the current in this circuit. An adequate value for this resistor isRpullup = U/I = 5V/8mA = 0.625kOhms.
We chose a value of 15kOhms which gave good results and makes sure that the chip won't suffer from a too high current. At the same time we ensure a low input current IB for the transistor.
This current can be calculated with the measured output voltage at the gate of Vgate, out = 4.6V
IB=4.6V/15kOhms=0.3mA.
The transistor subsequently turns on a second circuit with a different power supply and an LED as load. The same resistor R=15kOhms limits the current in this circle to 0.3mA which is sufficient to turn on an LED.
The LED turns on when both switches are pressed, because the the input voltage is equal to ground Vinput=Vground. In a next step we connected both of the input ports which made the NOR gate work as a NOT gate.
For the next task we replaced the LED with a pager motor. Hence this one needs more current to work, we replaced the resistor in the second circuit with a 5.6kOhms.
Timer Chip - Oscilloscope
In order to obtain a square wave, we built up an astable timer circuit. The circuit diagram is shown in the next figure.
The frequency of the tone can now be determined by the following formula:
We used potentiometers for the resistors so the tone is adjustable by hand. Although it's quite difficult to hit special frequencies with it.
No comments:
Post a Comment