• 13/07/2015 - Design Analysis

    Holly Wright • 07/16/2015 at 01:28 • 0 comments

    Attendance: Holly, Rob, Wilson, Tom and Lachlan

    Tom brought an old phone so we took some measurements.

    Holly’s Headphones40 ohm on speaker, 17Mohm on mic
    DC bias mic output0V if mic detected, 0.8V if mic not detected
    Mic detection 2V DC output on device plug in, if > 800 ohm is detected the phone will recognize the microphone, otherwise it will need to be removed and plugged in again.

    We did some circuit development, talked about the current features and looked at ways of making them better. These were the results.

    Next actions:


  • 09/07/2015 - Circuit dev

    Holly Wright • 07/16/2015 at 01:18 • 0 comments

    This session we came up with a basic plan for developing a prototype.

    Brought some components and gave them to Lachlan to build something before our next meeting.

    Between this meeting and the next meeting Lachlan built a circuit and these were the notes taken:

    Notes on First Prototype Build

    Attempted by Lachlan

    OP-Amps

    The OP-Amp used for the first prototype is not a ‘precision’ OP-Amp. Probably means that the slew rate is slower and there is more noise. This may not affect the build but it is worth noting if an improvement to the quality of the signal is required.

    The LM1458 has a required voltage supply of 22V. This is not suitable for our purpose. Moving to using the LM3412N as this is the only other OP-Amp available.

    Polarised Components

    All components on the signal side of the circuit need to be unpolarised. It is an AC signal being measured.

    Practicalities

    It would have been much easier if I had all the right gear. Was missing a breadboard with power rails, solder, an accurate way to read the data in real time (was going to use the Arduino but needed to download extra software which took time) and some components weren’t quite right (the caps were polarized, the OP-Amp was not ‘precision’, the pot was 10k not 1M and didn’t have a bipolar LED so used to LEDs in parallel facing opposite directions which may or may not have worked).

    Function Generator

    I downloaded ‘Audacity’ as this has a tone generator function in its dropdown menu ‘Generate – Tone’. Take care using this!! The audio plug is apparently quite sensitive so it is not hard to wire something up to it incorrectly and break the audio plug or sound card!

  • 02/07/2015 Brainstorming

    Holly Wright • 07/09/2015 at 11:45 • 0 comments

    Brainstorming ideas, oscilloscope plugin was decided a winner.

    Developed a timeline, scope, identified concerns. Outlined action items:

    Research: prior art, has it been done before, can we use multimeter tech

    Design: current limiting, voltage reduction, circuit protection/fuses, mechanical design

    Development: Breadboard then Veroboard then PCB

    Requirements: to investigate

    Concerns: can we make it possible for DC? Has it been done before?