Week 8

Week 8 Rube Goldberg 

In our Rube Goldberg machine we will combine several circuits we used in previous weeks to combine a digital display, motor, relay, opamp, temperature sensor, and a LED to hit a ball off a tee.

In our set up we have our clock sending a signal to our counter; the then counter is sending a signal to the driver, then the driver controlling the digital display. The display will continue to count from 0 to 9, once it past 9 it will start over.

Whole circuit, and setup

We connected the inputs of a XOR gate to the C and D outputs of the counter. Then we connect an LED to the output of the XOR gate to show when the logic gate runs true. The logic gate will run true when the display is between 4 and 9.

From the truth table and the table of the outputs of the counter you can see the green LED will be on when the display if between 4 and 9. Between 4 and 9 either the D or C input is high, but never both at the same time.

XOR Gate(7486) Truth Table

 

Truth Table for the counter

In the picture below you can see that the display is not between 4 and 9 and the green LED is not on.

Figure 2: Display 3,green LED not on

As you can see in the picture below the display is now between 4 and 9 and the green LED is on.

Figure 3: Display between 4 and 9, green LED on

We have a blue LED connected to the normally closed terminal of the relay, so it will be on when the relay is not engaged. 

Figure 4: Relay not engaged, blue LED on

We have connected a clear LED to the normally open terminal of the relay to show when the relay is engaged for testing. When we engage the relay you can see the clear LED come on and the blue LED go off. In the photo we manually changed the relay by applying 6 volts to the solenoid for testing purposes.

Figure 5: Relay engaged, blue LED off, and clear LED on

We now have connected the output of the XOR gate and the output of the normally closed terminal of the relay to a AND gate. The output out of the AND gate is connected to the yellow LED light to represent out motor. Following the truth table for the AND gate below you can see that the yellow LED will turn on when both the relay and the XOR gate run true.

AND Gate (7408) Truth Table

In the photo below you can see clear LED is on showing that the relay is engaged, but the green light is not on showing that the XOR gate is now true. Which doesn’t turn on the yellow LED.

Figure 6: Relay engaged, clear LED on, green and yellow LED off

Now when the display is between 4 and 9 the green LED turns on, this make the logic for the and gate run true turning on the yellow LED.

Figure 7: Relay engaged, display between 4 and 9, green, clear and yellow light on.

We connected the temperature sensor to the op-amp in a non-inventing configuration. Then the amplified signal will go to the solenoid of the relay. When the temperature sensor is heated with the blow dryer it will engage the relay.

In the video below you will see the whole circuit in motion. The display will repeatedly count from 0 to 9, the Green LED will be on from 4 to 9 on the display, the relay will engage when the temperature sensor is warm enough, the motor will spin once the green LED is on and the relay are both engaged. The motor will then send the ping pong ball flying.

Video 1: Full circuit in motion. 

Problems we had

We first notice that the display was counting too fast for our setup, so we had to reconfigure the set up of the resistors on the clock to slow the clock speed down. We increased Ra from 150k ohms to 330 ohms. Then we increase Rb to 820k ohms. Below you can see out clock set up.

We had an issue with the AND gate running true with only one input of 1, from the truth table of an AND gate we know this is not right. We found that the one input of the AND gate that was not one need to be ground to the AND gate to function properly. So we ground the inputs, but this caused and issue since electricity is lazy and flowed the path of least resistance and with the inputs grounded the signals coming from the relay and the XOR gate would go straight to ground. So we instead of directly grounding the inputs we used a 1k ohm resistor to ground them. This then forced the signals to go to  the AND gate and not straight to ground.

The last issue we had was that we found the output of the AND gate was not strong enough to power the motor. So we thought about the first time we built a Rube Goldberg circuit with a transistor and the light sensor. We used the same set up but replaced the photocell and the 5 v supply with the output of the AND gate, thus allowing us to turn the motor with an AND gate.