1. Power and energy

1.1. ShortSquawker power

ShortSquawker page

short squawker complete
Figure 1. ShortSquawker system schematic
What is the expected current drawn from the battery according to the schematic of Figure 1?

Answering this requires setting expectations, predictions, and assumptions about the MCU’s operating mode!

  • First consider the current drawn by the low-dropout voltage regulator (LDO) U1.

    • Perhaps an AMS1117 (common and cheap). (datasheet)

    • Or the LP2985 (datasheet)

    • Which one of these is better for this application?

      • ¿¿ What does “better” even mean in this situation ??

  • The only thing that the LDO supplies is the MCU. So, what is the expected supply current of the ATtiny85?

    • Split into multiple sub-components! Break down a large problem into smaller parts that interact with each other — a fundamental and high-quality problem-solving approach!

ShortSquawker — Selecting Rsource for the more accurate estimate of pin current.

2. Activity

shortsquawker currents
Figure 2. Supply current components

  • Split into ≈ 7 groups, one per leaf node of Figure 2.

  • Use datasheets, Figure 1, circuit analysis, and other tools to estimate the current drawn by each sub-unit.

    • 20-30 minutes

  • Report out at the end of class:

    • Your sub-unit.

    • Estimate of supply current.

    • What factor most influences this value — i.e. what “knob” is available to the designer to reduce the total system power usage.