During the first week of the design/implementation semester, the team began working on the preliminary steps of implementation. This included test circuit assembly, microcontroller programming, and investigation into a solution for the AC power supply modification that was suggested by the panel last semester.
John
During the first week, John began assembling the breakout PCBs for the TSSOP stereo CODEC ICs from cirrus logic. The TSSOP package is extremely small. Soldering the IC to a breakout board will allow for easy breadboard testing and troubleshooting via header pins.
Solder paste was used in to limit the chance of damaging the chip by excessive heat exposure.
Cirrus Logic CODEC soldered to TSSOP-28 Breakout Board w/Quarter for Scale
John Also Attempted to solder some shielded 24 AWG stranded cable to the terminals of a MEMS mic, but the cable was too large and the tension caused the traces of the mic to be ripped from the PCB. Luckily the team ordered 6 of these mics in order to account for such casualties.
The 24 AWG Stranded wire is too large and rigid to allow for a resilient solder connection
While searching the aisles of Skycraft for a smaller wire gauge, John stumbled upon a few 24V 2.7A AC to DC power supplies priced at 5.95 each. He purchased two of them to see if they could be arranged for a split-supply operation.
The supplies inputs where connected in parallel to the 120V AC mains via a 2 prong Edison connector. The outputs where then connected such that the positive of one supply was attached to the negative of the other. Measuring from this center connection to the remaining open positive and negative terminals yielded around +24V and -24V respectively. Measurements were performed with a Velleman PCSGU250 USB scope.
The two Skycraft supplies connected as described w/ scope probe connected across positive branch
Scope plot reads a DC Mean value of 24.4V
Probe connected across Negative branch
Scope plot reads DC Mean of -24.1 V
Although Hunter has also worked on a solution for the power supply, the ones found randomly at skycraft could be easily upgraded with additional linear regulators in order to supply the lower voltages (12V, +-5, and 3.3V).
Hunter
The first week of the design implementation phase was primarily focused on finding an AC-DC power supply that could supply the 6 various output voltages, that John mentioned above (3.3V, +-5V, 12V, +-18V).
Although, John was fortunate the day he went to Skycraft and found a working power supply at a low cost, which will also do the job, I will continue to discuss the other option that was being considered that I researched, since this consumed the majority of my time for this week.
There are obviously a number of ways to create an efficient AC/DC power supply, but before John found the one at Skycraft, the kind that I was considering was a desktop computers Power Supply Unit or (PSU). Even though most of these are an overkill for our application, when it comes to power and size, it seemed like the and best and quickest option without having to make a lot of modifications or a custom power supply, for now, since time is a factor.
The PSU (shown below) had the smallest footprint, that I could find, for a PSU that had the amount of outputs we needed, was at decent price point, and ended up being just a few inches larger than than the supply my teammate found. Although, these typically start around 300W and up, the lowest power found that included all our specifications and the smallest footprint was 220W. [1]
The reason this PSU stood out is because it seemed to require the least amount of modifications, and ended up having somewhat of a small footprint when compared to others PSU's.
The minimal modification would be a result of it already providing, almost, all the outputs we need, with multiple outputs for each value to spare. This PSU has multiple 3.3V, +-5V, and 12V outputs and some (including this one) have a single -12V output.
All the wires are also visually easy to identify being color coded, as shown in the connector reference below. [2]
The only modification that this supply would require is for the +-18V output, which could be amplified/boosted with any of the other outputs (preferably 5V or 12V), by applying a single, Dual Operation, TLV1702-Q1 microPower Comparator made by Texas Instrument and designing it to supply the +-18V. [3]
The data sheet shown above, and below, shows how this component offers a single, dual, or quad comparator(s) within the IC device, with each comparator providing a minimum of 2.2V (+-1.1V) up to 36V (+-18V) output. So for our application only one Dual Operation (TLV1702) device would be needed to achieve both the 18V and the -18V outputs.
Upon discussing our research, John's power supply ended up being half the price, including the extra components, and a little smaller than the PSU option so we are moving forward with the power supply from Skycraft.
This week I also added a new Time and Effort table for the design implementation phase. The version is properly aligned and has no embedded links, so our progress can be added straight to the sight to increase load times.
To use it we must click on the small white box located at the top left side of the table (shown below), which is only seen in the edit mode.
Upon clicking the small white box, the Content Manager opens (shown below) where our information is typed under the specified columns and automatically updates to the main Time and Effort page. It is also in numerical order, with the most recent date being displayed at the top row, as requested in the previous semester.
The weekly minutes with the professor page was also updated this week:
References:
[1] “220W Power Supply Unit for HP Pavilion Slimline S5,” Amazon, [Online]. Available: https://www.amazon.com/TouchSmart-310-1205la-633195-001-633193-001-FH-ZD221MGR/dp/B07JYNMXJV [2] Lazar Rozenblat, “ATX Power Supply Pin-out and Connectors,” smspowersupply, 2008 (Revised 2017), [Online]. Available: https://www.smpspowersupply.com/connectors-pinouts.html
[3] Texas Instrument, “TLV170x-Q1 2.2 to 36V, microPower Comparator,” TLV1701-Q1 datasheet, October 2015 (Revised December 2019).
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