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Power Supply Considerations

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cstratton edited this page May 14, 2016 · 1 revision

We want a cheap, simple, safe power source.

  • 2x AA or AAA batteries

NiMH is 1.1v per cell discharged, alkaline is 1.65 volts new, so that's a range of 2.2 to 3.5 volts. Both are within range for an RFM95 and a KL25Z or similar ARM MCU. But what does that do to the ADC range? Also, can the RFM95 transmit at full power with a reduced voltage?

  • Boost converter to 3.3v. Suggestions for a cheap, easy to use one? Ideally we don't want to waste a lot of power while in sleep mode just keeping the MCU memories and low-speed clock alive.

  • Run MCU and radio off batteries, have a 3.3v or even 5v boost we can enable to power sensors?

How can we have a node that runs off batteries, but also USB power when connected to a development host? Can we use a PFET, Arduino-style to enable the batteries, and disable it in software when we see USB power? If there's a diode from the USB power/regulator to the MCU power rail, will turning off the FET in software be fast enough?

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