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I'm working on a project that includes an ESP8266 (requires 3.3v input (250 mA peak)) and a HC-SR04 (requires 5v 20 mA peak). I'm making it battery/solar powered.

I'm trying to keep costs down as well as make a system that works reliably and has good longevity.

I'll be waking the device every 15 minutes and keeping it in deep sleep at the other times.

Originally I was going to use a battery source over 6v, like a 6 cell AA rechargeable battery pack, a 10v or so solar panel, and a breadboard type voltage regulator that conveniently provides 3.3v and 5v on the same board. This seems to waste a decent amount of power though.

Right now I'm looking into using a 2 AA rechargeable NiMH batteries, a 5v solar panel, a 3.3v step up voltage booster, and a 5v step up voltage booster. 5v step up voltage boosters are everywhere and cheap because of their uses for portable cell phone chargers. 3.3v step up voltage boosters on the other hand are more expensive and harder to find.

Looking for any advice or affirmation that I'm on the right path. Thanks!

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That sounds reasonable. The only issue is the necessity of a couple of voltage converters. The other choice is to have 5V step-up converters and a 3v3 LDO for output.

An alternative approach, I used, is to use a (locally available) 4v1 1000mAH VRLA battery with 6V solar panel and a couple of Schottkey diodes. I used a LDO (XC6206 - datasheet here) to ensure a 3v3 Vcc (or Vdd).

If finding VRLA is difficult, a Li-ion or Li-po could be used, but you might need a charge controller (e.g. TP4056 - datasheet here). That's why I prefer VRLA batteries as they are more forgiving with the charger circuits.

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  • \$\begingroup\$ Thanks for the great advice! Would there be any issues with going from a battery (2 AA Eneloop batteries (~2.4v)) to a 5v step up booster to a 3v3 LDO? I'm just wondering if the esp8266 would be able to get it's needed 250 mA for WiFi transmissions. Also the VRLA battery idea is interesting. I actually bought a cheap solar powered flashlight to source it's solar panel and battery which happened to be a sealed lead battery :) Using this method I could run the LDO to the esp8266 and a booster to the HC-SR04. \$\endgroup\$
    – Paul Masek
    Commented Nov 8, 2015 at 7:55
  • \$\begingroup\$ With a 5V up converter efficiency of ~90%, this config would consume (5 * 0.25 / 0.90) ~= 1.39W at peak. As long as the booster could provide needed current at 5V without switching noise, I couldn't see any further issues. Which converter are you planning to use? BTW, I always attach a strong bypass capacitor pair like 100uF + 0.1uF. The only other issue I see is: 5V up converter is online even when the controller is in deep sleep. There'll be some battery drain there. And yes, the VRLA config is working fine for me for about three months now. I left it (practically forgot it) in the garden. \$\endgroup\$
    – Vasu
    Commented Nov 8, 2015 at 17:38

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