P19361: Optoelectronic Guitar Pickup
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

The team's vision for this phase is to complete all feasibility analysis that was delayed due to late parts. Population of David Malanga's V2 board will also be completed during this phase. After populating this board, the PIC will be programmed with the latest DSP software from David. Preliminary designs will be completed for the sensors, as well as the casing and adjustment system. Prototypes will be made to show how our sensors and mechanical system will work together. A guitar routing plan will be created once the sensor designs are finalized.

This phase, the team completed the feasibility for a reflective pickup. Thanks to a friend of the teams, Anmol Modur, a sensor has been selected for the reflective design. Mechanical and electrical preliminary designs are completed for both the reflective and transmissive pickup. Prototypes are being worked on to show how the pieces will work. The V2 board is finally populated, minus the PIC being the wrong size. Clarification with David will be needed to determine which part number is the right one for the PIC so we can order a new one.

Feasibility: Prototyping, Analysis, Simulation

Question of Feasibility - Reflectivity of Strings

Will the reflective pickup have enough reflection to replicate the string vibration into sound?

Assumptions

Materials

Procedure

  1. Align IR LED and photodetector under guitar string based on setup from morphological chart
  2. Hook up power source to IR LED and Photodetector, hook up photodetector with oscilloscope to track what the photodetector sees
  3. See if photodetector is detecting IR through Oscilloscope
  4. Pluck string. See if the oscilloscope shows drops in voltage, as the string should be reflecting the IR to the photodetector
  5. Find a clear threshold from the oscilloscope capture

Results

While attempting to test the IR LED and photodetector, a friend of the team stopped in and suggested we use a SparkFun QRE1113 chip which reflects infrared light off a surface above the sensor and receives it. This friend provided us with a breakout board of this chip and we were able to test and show that a clear signal is received. Below is the signal received when the sensor was placed under the low-E string and the string was plucked.

Oscilloscope Capture

Oscilloscope Capture

Looking at the measurements, the frequency measured by the oscilloscope shows roughly 82Hz, which is about the frequency of the low-E string. This shows that we should be able to process this signal and use this sensor as a part of the pickup.

We also noticed that the signal's peak-to-peak value decayed as the strings volume decayed.

Concept Selection

Reflective Concept Selection

SELECTION

Transmissive Concept Selection

SELECTION

Drawings, Schematics, Flow Charts, Simulations

Reflective Design: Electrical

Oscilloscope Capture

Oscilloscope Capture

This design is based on the Sparkfun analog line sensor board and previous revisions of the optical pickup project. The resistor values from the Sparkfun board were used, and a trim-pot will be used on the receiving end to allow fine tuning of the signal level at the input. These values are not final and will be tested.

Reflective Design: Mechanical

Reflective Assembly

Reflective Assembly

Reflective Adjustment Assembly

Reflective Adjustment Assembly

For the reflective design, we decided to go with the screw+spring arrangement. A thumb screw moves the sensor transversely to the strings, while two screws connected to the top plate with springs control the height and angle. The sensors and thumb screws will sit below the pick guard and will be covered so they cannot be altered when playing.

Transmissive Design: Electrical

Oscilloscope Capture

Oscilloscope Capture

For simplicity, the transmissive pickup design will utilize the same QRE1113 transceiver as the reflective design, but it will utilize two of them and only use the transmitter half of one and receiver half of the other. Otherwise, the circuits are the same, the switching configuration to activate them will just be different.

Transmissive Design: Mechanical

Transmissive Assembly

Transmissive Assembly

Transmissive Adjustment Assembly

Transmissive Adjustment Assembly

Since we are using the reflective sensor as the bottom IR LED, the bottom adjustments are the same as the reflective arrangement. A removable bar is added above the strings to hold the LED's. This bar uses an L bracket with two set screws to allow for adjustment transversely to the strings, along the strings, and to and from the strings.

Software Flowchart

Software Flowchart

Software Flowchart

Bill of Material (BOM)

Bill of Materials

Bill of Materials

So far, we have spent roughly $50 on parts for prototyping and shipping costs. We anticipate that shipping costs will be less moving forward as we start ordering more parts per order as our design and concept selection become more finalized. More analysis needs to be done on what the project will cost as a whole (such as how much fabricating a new 4 layer board would cost/how much the parts to populate a second V2 board would cost), but we anticipate at this time that it will be under budget. See this spreadsheet for links to the parts that have been ordered.

Test Plans

Test plans are being developed for the engineering requirements. The current test plans developed so far are shown below.
Test Plans

Test Plans

For more information on these test plans, see this excel sheet where the information is being edited.

Risk Assessment

This is our risk assessment for this phase. There are no new risks comparing this assessment to last phase's assessment.
Risk Assessment

Risk Assessment

Design Review Materials

Our design review will be held on 11/12/18 at 5pm, in room 4425. Please see the following documents for our review:

Plans for next phase

The following tasks are to be completed by the team over the next phase.

Team Plans

To see each individual's plan for next phase, see this link


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