Yao's Week 12

Blog sheet Week 12:

This week’s blog sheet will be individual but you will post it on your group blog.

Your individual Rube Goldberg (RG) setup should satisfy the following:

1.     Use at least 2 of the following components:

a.     Transistor

b.     OPAMP

c.     Relay

d.     Temperature sensor

e.     Photosensor

f.      Motor

g.     Display

h.     Strain gauge

i.      Speaker

j.      Microphone

k.     Solar panel

2.     Use a new circuit: It can be a modification to one of our lab circuits.

3.     Let your system complete its task in no shorter than 10 seconds.

4.     Make sure you are compatible with your preceding and following RG stage.

Your blogsheet 12 tasks:

1.     Provide the computer drawing for your individual RG setup.

Figure 1. Circuit Design of Rube Goldberg set up

2.     Explain your setup.

As figure 1 shows, I used Opamp, half-rectifier, photocell, transistors, relay, and motor in my Rube Goldberg design. The photocell will be the trigger for the whole design.

The first part is an Oscillator (Opamp), which can give us square wave output, and it can work as AC signals source.

Then the second part makes up by half- rectifier, two 3.3kΩ resistors, and photocell. Half rectifier can convert AC signal to DC signal, and then two resistors work as voltage divider. When there is room light, the photocell has high resistance, and because the photocell is parallel with the 3.3kΩ resistor, then the output of second part will be high-level (voltage divider theory); When there is flash light, the photocell has low resistance, and the output will be low-level.

The third part will be R7 and the transistor Q1, the output of second part will be the input of the third part. If the input signal of the third part is high-level (which means room light condition), then the transistor will become on-state, which means the output will low-level; If the input signal of the third part is low-level (which means flash light condition), then the transistor will become off-state, which means the output will high-level. The output of the third part will connect to the second transistor Q2.

The second transistor Q2 works similarly to the first transistor Q1: If the input signal of the Q2 is high-level, then the transistor will become on-state, which means the output will be low-level; If the input signal of the third part is low-level, then the transistor will become off-state, which means the output will be high-level. The output of Q2 will connect to Relay’s Pin 2.

Relay works as switch here. Pin 1 will connect to the voltage source +9V, and it will be the amount of voltage sent to Pin 3 or Pin4; Pin 2 will connect to the output of transistor Q2; Pin 3 will connect to the motor; Pin 5 will also connect to +9V. If transistor Q2’s output is low-level, Pin 3 will work, and then the motor will spin (Pin 4 is not used here).

3.     Provide photos of the circuit and setup.

Figure 2. Rube Goldberg set up

Figure 2 shows the circuits and the set up of the Rube Goldberg on the breadboard.

Figure 3. The output signal from Oscillator

Figure 3 shows the output signals from Oscillator part, and its square wave (AC signal), which is what I expected.

Figure 3. The output signal from half-rectifier 

Figure 3 shows the output signal from half-rectifier, and it was not square wave, which also met my expectation (the signal has been converted the DC signal).

4.     Provide at least 2 videos of your setup in action, one being a failed attempt.

Video 1. Failure Attempt 

Video 1 shows that the motor was always spin, no matter with room light or flash light.

Video 2. Successful Attempt

Video 2 shows the Rube Goldberg set up worked successfully.

5.     What failures did you have? How did you overcome them?

      The first failure was that the motor was always spinning no matter under room light or flash light, which as video 1 shows. I think it might because the values of resistors are too large (the voltage divider part), so I changed the resistors to smaller values (two 15kΩ resistors to two 3.3kΩ resistors). However, it still didn’t work. After the power supply was turned on, the motor start to spin for few seconds (just with room light), then it stopped spinning, and even I turned on the flash light, the motor didn’t spin either.  Finally, I figured out the reason was bad connection between the second transistor and breadboard, after putting the transistor to the right position, the whole set up worked successfully.