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The display working and not working

I have an esp8266 on a breakout board for programming hooked up to an OLED via GPIO 0 and 2. It works fine if I power it via the FTDI/USB. It also works when I power it at 2.8-3.0V using a desktop variable power supply. But no matter how I connect a battery it won't work. I don't want the breakout board in my final project and I want it to be powered by lipo. I've tried making a voltage divider but the divider did not produce the voltage my calculations indicated.

I have 220 and 550 ohm resistor to bring the 4.04v of the battery down to 2.9v but when connected it takes it down to 1.1v which is not enough to power the esp8266 wifi module. I tried adding a capacitor over the +/- rails to improve the current, but I'm honestly still learning how that works.

The esp8266 works fine at a wider range of currents but the OLED seems to be very sensitive.

How can I get this working with the battery?

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  • \$\begingroup\$ How about you add a Regulated Power supply IC for the OLED? Because USB and Bench supplies are regulated. This is a premature suggestion; but likely this is the cause. \$\endgroup\$
    – ammar.cma
    Dec 7 '15 at 20:28
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Your resistors are limiting the current of all your loads. The OLED module is the most sensitive to such limitations. As stated in the comments, you need a voltage regulator.

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Without going and looking up your (unspecified, as far as I can read) OLED part, I'm not sure why you think you need to divide down a 4V battery if it "works fine" when powered off 5 V USB, unless you are doing something else when powering from USB (I guess the breakout board is powering the display in that case?)

Voltage dividers (your 220 and 550 ohm resistors) are lousy voltage regulators. When you draw current from the middle junction, the voltage changes.

For a basic "learn something" experiment you could try 22 and 55 ohms, making a much "stiffer" voltage divider (yup, wastes lots of power as heat) but a more practical approach is to use an actual voltage regulator, such as a LM317 (boring old part, there may be better new and exciting choices.) Another option for small non-critical things is to run it through a diode or two, using the diode drops to burn off the excess voltage 1.0~0.4V at a time depending on the diodes and current; ie, 1-2 silicon, non-schottky diodes (or 2-5 schottky's) in series between the battery and the device.

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  • \$\begingroup\$ It's never worth powering anything off a voltage divider. \$\endgroup\$
    – pjc50
    Dec 7 '15 at 22:26
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    \$\begingroup\$ When you're starting from powering it off a wimpy voltage divider, the experiment of using a stiffer divider is a potential learning experience - and that can, as actually suggested, be followed up once the experiment has been made with something more suitable in the voltage regulator line. \$\endgroup\$
    – Ecnerwal
    Dec 9 '15 at 21:18

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