For this week's videos/readings we looked at both sensor interfaces (as an introduction to serial communication) and datasheets. My notes:
Biggest takeaways:
- The simplest sensors measure resistance/capacitance, a little bit more complex has circuitry built in that converts some inherent property to changing voltage.
- Some sensors have built-in microcontrollers that can send data to another microcontroller instead of change in voltage.
- Within datasheets, look for description, pin diagram, and supply voltage and current (both the range that the component can safely handle and the recommended range).
- Not sure what the conversions mentioned in the videos were?
datasheets
As an exercise, I looked into the datasheets for the components of my LED earrings project (will I ever have time for it? lol idk I hope so someday).
LED
For the LED, I'm going to experiment with the reels of surface mount LEDs on the floor, whose part number is 1830-1080-6-ND. According to its datasheet:
- PCB type molding style (?)
- Package dimension 0805 (2mm x 1.25mm according to this wiki)
- Forward voltage 2.6–3.4V for white LED
- Forward current 5mA for white LED
battery
For battery, I was interested in their size (the smaller the better), their nominal voltage, and typical capacity (I think this is how long the battery can supply current for).
| battery | dimensions (diameter x thickness, mm) |
nominal voltage | typical capacity (mAh) |
|---|---|---|---|
| Energizer CR2032 (coin cell) |
20 x 3.2 | 3.0 | 235 |
| Energizer CR1220 | 12.5 x 1.6 | 3.0 | 37 |
| Energizer 379 | 5.8 x 1.95 | 1.5 | 14.5 |
Which means that the coin cell can power the chosen LED for ~47hours, the CR1220 for ~7.4hours, and the 379 won't even work because it doesn't supply enough voltage.
battery holder
Now that I know CR1220 is the size I want to go for, I went on Octopart to search for a corresponding holder by filtering the case/packaging to SMD and diameter to 12mm. That narrowed down to two options, only one of which was in stock: BK-885-TR.
The most important information from its datasheet is its overall dimensions: 19.54mm x 12.7mm x 3.17mm.
And because CR1220 would only be able to supply current for ~7hours optimally, I'd want a discrete on/off switch for it. Knowing that my battery holder would have a height of 3.17mm I tried to find a button with a similar dimension and landed on EVQ-P4403M. Its dimensions are 6.2mm x 3.5mm, but the problem is I don't think it maintains state (and the ones that do have a much bigger profile).
resistor
I couldn't find a 200ohm surface mount resistor in the shop, I will keep looking. In the meantime, I did search some up on Octopart and am wondering what the wattage means for a resistor.