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Team Vision for Preliminary Detailed Design Phase
During this phase, the team created a BOM, and put together designs for the transmitter and receiver hardware, enclosures, and software. Test data from some laundry machines was obtained, and a list of possible machines with their respective specs was started.
Prototyping, Engineering Analysis, Simulation
The next couple of diagrams show models of what the transmitter and receiver diagram of the enclosures will look like:
The transmitter enclosure is below, showing the connection to the wall for a 120V connection. All transmitter hardware would ideally fit inside of this enclosure. The original document can be viewed here,
The prototype enclosure of the receiver is shown below There is a 3D rendering of the enclosure as well as a 3D print of the enclosure. This was an open source design. This design is to modified to be more robust and scaled to fit all the components of the design.
Feasibility: Prototyping, Analysis, Simulation
To start off, a list of various washer and dryer brands/models was created, which included the various power, voltage and current draws that could be found in their respective specifications. This gives a rough idea of what the maximum specifications for components used in the transmitter design will need so they are not over-saturated, as well as the minimum values that may come across. A small snippet of the list is shown below, and the full document can be viewed here.
After running simulations on device safety via LT SPICE, it was found that the voltage protection initially used for the ESP32 would not be sufficient for the design, or rather it has the possibility to underpower the board. It essentially implemented a very crude linear voltage regulator, so due to its undesirable performance shown below, it was omitted from the design.
When drawing 113mA, the output at the emitter of Q1 drops to 3.277V, which means the 3.3V linear regulator will not work, and the ESP32 may not work properly.
Drawings, Schematics, Flow Charts, Simulations, etc.
Over the course of this design phase, the team has put together designs for both hardware and software portions of the Laundry Bug.
The first couple of diagrams depict a more in depth view of the hardware setup for the transmitter and the receiver:
Shown below is the schematic that was used to verify the signal conditioning circuit:
Shown below is also the waveforms that were generated from the input and output:
The blue signal is the input waveform which has 5Vpp, and the green signal, which is the output has about a 1.2V offset. The output is also within the 3.3V maximum voltage measurement for the ESP32. The signal is also inverted, as the amplifier has been set up in the inverting configuration, but this should not matter since the measured current will still be the same.
The transmitter diagram, drawn up in CircuitMaker, shows how the device would take current samples from the laundry machine, and how the microcontroller would be shielded from the high voltage that comes in from the wall connection. The schematic's original file can be viewed here. Both schematics will be drawn up in Altium Designer, and the PCB design will be started for the next phase.
The receiver diagram shows how the battery voltage will be boosted from a low voltage to a higher voltage. This design is intended to use 2 1.5V AA size alkaline batteries. The battery life and current needed to run the ESP32 will need to be determined with feasibility testing. On the right side of the schematic, a piezo buzzer is used to notify the user at the end of each cycle. The schematics will be drawn up in Altium Designer, and the PCB design will be started for the next phase.
The final Flow Chart depicts how the software will flow once coding is written. With the idea that there will need to be some delay between the laundry finishing its cycle and the notification being sent, the coding was developed with roughly a 1 minute buffer or hysteresis. The original document can be viewed here.
Bill of Material (BOM)
Shown below is the BOM that could be used for a simple design of the transmitter. It is built around the ESP32 devkit and only requires a suitable power supply and signal conditioning for the current sensor input.
The BOM shown below is based heavily on the Expressif ESP32 devkit schematics. The parts for the programming interface have been omitted in order to save on production costs, as the LaundryBug is intended to be programmed once at the factory.
Shown below is the BOM for the receiver.
The file for all 3 BOMs are here.
Test Plans
Purpose
For testing, the team needs to gather information on various laundry device currents by use of a current sensor, as to get a better grasp on how much of a range the hardware needs to cover for safety, and the software needs to cover for accuracy.
Some of this testing has already been started using devices and circuits below.
This is a picture of the current clamp that was used to measure the current drawn by the washer/dryer. When current flows through the cable a proportional current is induced on the coil inside the clamp which is read by the microprocessor. Due to how the device measures the current the clamp must be wrapped around one of the conductors of the cable. To make this possible across multiple devices without modifying the existing wiring the sheeting of a one foot extension cable was removed and the clamp attached to the black conductor.
This is a picture of the circuit that allowed for the information coming from the current clamp to be read into the Arduino. Since the Arduino input pins can only accept a positive voltage, a DC bias needed to be added to the signal To do this, two resistors are used to divide the 5V coming from the Arduino. A "current output" current transformer needs to be used with a burden resistor, and the burden resistor completes the current transformer secondary circuit. The capacitor provides a path for the alternating current to bypass the resistor, as well as helping to prevent any fluctuations in the applied voltage.
Several graphs of the test data are shown below. They are all from different machines; two washers and one dryer. The full list of tests currently completed can be seen here.
First: Samsung Washer, normal wash:
Second: Kenmore Washer, normal wash:
Whirlpool Dryer, normal dry:
As more tests are run, the coding for the device can be further refined, guaranteeing that the device has an overall accuracy of at least 95%.
System Design and Flowcharts/System Block Diagram
The System Design Flow Chart is from the previous Design phase, which has been updated to show that there is both a receiver and a transmitter in the design of the device. The original file can be viewed here.
Risk Assessment
No new Risks have been added, but the likelihood and severity, as well as the consequent importance needs to be evaluated for all of the risks.
Design Review Materials
Links to:
- Pre-read
- Presentation and/or handouts
- Notes from review
- Action Items
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