Question

In the final project, students will design a motor controller based on the light level on a phototransistor. When illumination is very high, the motor will be stopped while 6 volts will be applied to the motor under low light conditions. You will need to measure (characterize) the properties of a phototransistor under both light and dark conditions in order to design the circuit and calculate component values. An op amp is be used in the project along with a TIP-29 transistor. A 20 point penalty will be imposed if the circuit can only drive a resistive load successfully instead of the motor. Good parts layout along with the use of bypass capacitors will greatly increase the likelihood that the circuit meets all specifications.

Students working in a group of two will also need to provide an audio signal that is a function of the light level. Here, a CMOS 555 timer is to be used as a voltage controlled oscillator (VCO) that will generate a tone at a frequency of 500 Hz (+/-20%) at zero light level and 1500 Hz at full light (0 volts applied to motor). A small speaker or headset can be used to make the output audible. One possible circuit is provided in the project data sheets folder (555CVCO.ASC) which can be used as a starting point. Students are free to use other circuits given on the web if they wish.

Please do the 2nd part that two students need to do it

Please do it as soon as possible

Answer 1

The second part of the question is to create a Voltage controller oscillator using 555 timer IC.

A 555 timer IC desingned as astable mutlivibrator will generate continouous square wave. to convert the same circuit

as a VCO, terminal 5 of the 555 IC is used as a voltage input.

Consider the circuit above. where 555 is designed as a VCO.

For resistance Ra and Rb =320 Ohm and C = 1microfarad and input terminal5 is at 0V then astable multivibrator will generate 1500Hz. which is the requirement for 0 volts at full light condition.

With same Ra, Rb and C to generate 500Hz at 6volts input for no light condition. by providing a Vcc voltage of 9V

555 will generate 500Hz.

A series resistance of 220ohm can be provided across speaker. If a variable pot of 1kohm is kept that can act as a volume control.