10. Output Devices
Group Laboratory Work: Output Device Power Consumption
In groups we explored measuring the power consumption/power draw of output devices with 5 Volt DC fan motor. We measured the power draw of the fan motor when stalled and not stalled by holding/squeezing the rotating pin and again and calculated the measured for power using the formula below. The results of this experiment are in the table below.
We learned that in order to gain some of these measurements it is sometimes necessary to interrupt the circuit by implanting the positive and negative probes from the digital multimeter within the circuit in order to gain a reading of the current in milli-Amps. See sketch of interrupted circuit below. For example, we also measured the power draw of a red LED as a 5V output device. For this experiment it was necessary for us to interrupt the circuit with multimeter probes. The results from this exercise are also in the table below. Some would have guessed that the power draw for the motor when stalled would be lower if the motor used less energy to turn the rotating pin however, in the end we found that the power draw of the stalled motor was higher because the motor had to work harder to fight the resistance.
For additional notes and photos of our group work click here: Group Link
Data from Group Work as Referenced Above
Watts(W)= Volts(V) x Amps(A) *Current is measured in Amps and Power is measured in Watts; calculate amps by dividing milli-Amps (mA) by 1000
Exploring Mini Vibrating Motors as Output Devices
I decided to explore some output devices that could potentially be incorporated into my final project. I searched both Digikey and Amazon for miniature vibrating motors that seemed small enough to fit inside of a standard drumstick. There seems to be several brands of the two types of motors. One is a small button sized motor (actually smaller than a button) and the other is an eccentric rotating mass vibrating motor or ERM. Both of them come in many different sizes so I chose to the order the smallest ones I could find. Standard drum sticks seem to begin at 15mm in thickness while the button motor is 10mm wide. The ERM at 8mm leaves a little more wiggle room and is shaped more appropriately for being placed inside of the contraption. I wanted to test both motors to compare them but to do so I first had to solder jumper wires to both motors since the blue and red wires they arrived with were very thin and very flimsey. Even more importantly they were very short and didnt allow for easy maneuvering. I used a wire cutter to cut and strip the ends of the jumper wires from the lab but had to use an exacto knife to splice the end of the motor wires for both motors and peel the remaining wire coating by hand in order to not damage the thin wires. This was a great suggestion I got from my instructor that worked out perfectly. After twisting the wires to the jumpers, I soldered each connection and then placed heat-shrink tubing over each connection to make sure they were neatly contained. The end result gave each motor about 7 inches of extra length on their 2-wire connections. The red wire would go to power and the blue wire would go to ground and I could use either of the SMD pin sockets, the 2 socket or the 4 socket. I chose to use the 4 socket connection since those gave easy access to pin #4 where there is an output connection on my development board.
Testing the Mini-Motors
My initial test of the motors didn't require any coding so I just needed to find the correct connections to make on the development board. I first tested them in the 2 pin SMD socket which is wired to the 5V power and to ground. They both worked well with this 2-wire connection. The ERM video is below on the left and the mini button motor video is on the right. I did have to re-solder the 2 pin socket to the development board as the first motor tested shook the socket right off the board...lol. I realized then that I didn't use much solder to secure it to the development board so I reinforced it at our solder station. After powering up both motors it seems that so far the ERM motor seems to work the best for what I will need it for but I will continue to test other motors over the next few weeks.
Useful Files & Links for this Week
Data Sheet for Xiao Rp2040 Data Sheet for 2 wire ERM Motor Data Sheet for 2 wire Coin Motor Tactile Button Data Sheet Data Sheet for 2 & 4 Slot Pin headersProgramming an On-Off Button for the Mini-Motors
After experimenting with the two motors to see which would most closely resemble what I would need for my final project I decided to explore a little further. Powering the two motors was relatively simple but there isn't much that can be done with a motor that powers up and stays vibrating continuously. I had added three buttons to my development board so I wanted to see if I could program the black button to be a power button. This way the motor that was connected could be powered off and on. I performed a google search to see if I could find coding that would specifically work with the Xiao RP2040 but the results were not promising. I eventually realized that this was the case because I was using ERM and vibrating motor in the search along with my prompt. I then moved over to ChatGPT using the same search terms and what was generated was coding for Arduino IDE and the Xiao RP2040 that allowed a switch to turn and LED off and on. Since the LED is an output and technically is similar to/is a two wire connection, I decided to see if I could use the same code formatted to fit the pins that I would be using on my development board. I learned a lot about what my development board was missing during the week we explored input devices. Many of the useful pins on my board do not have traces to them from the SMD pin slots. I remembered that the input device that I had could not be wired to pins 1 through 4 on the right/bottom of the Xiao RP2040 as the chip is organized so that the top 4 pins on the opposite side work better with input devices. Because of this I decided to the connect the mini-motor to the 4 pin SMD socket that I knew had a direct connection to pin 4 which is an output pin and the GRN pin which is just below top right corner of the chip. I entered the pin #s into the code for the output device and was sure to identify the correct pin for the black button as well. I defined buttonPin as 26 and vibPin for the motor as pin 4. I changed the variables to reflect the motors in place of an LED, for example instead of ledPin I used vibPin.
Code for Button-Mini-Motor (Input & Output)
The code below was originally written for an LED output, as I described above but I was able to make adjustments to it so that it work as an on-off switch for the mini-motor. I did this by identifying the correct pins on the Xiao RP2040. As mentioned earlier I connected the button to pin 26 as an input device and the vibrating motor to pin 4 as an output device. The pin map that I have used most often is shown above. Tapping the button once powered the motor on and tapping it again powered the motor off. I believe I will be able to use this feature in my final project as an on-off switch. See video below. **To create this section of the webpage I learned about the "paste as html" in VS Code to paste the code that I used below.