user62375: I recently got an ESP32-01 Breakout and Development Board from EzSBC.com.  It is advertised as a board specifically designed for use with batteries because of it's low current draw when in sleep.
As a test I loaded the basic Arduino blink sketch onto the board using pin 19 as the built in test LED.  When I power the board from the computer through the USB connection the LED blinks as expected, but when I connect a battery accross VIN -> GND nothing happens.
What am I doing wrong?

user62375: There is a subtle design choice in this board that took be hours to figure out.
According the connection schematic the blue leg of the LS3528RGB LED is connected to IO19 through a 1k resister (R2-1).  However the power leg is connected to Vusb not 3.3V like the other RGB LED.  This means that the LED connected to IO19 is only usable when the board is connected through the micro-USB port and not when connected directly to battery.
This can be useful for programmatically reading whether the board is running on battery or USB. 

62375: <p>I recently got an <a href="https://www.ezsbc.com/index.php/featured-products-list-home-page/wifi01-35.html" rel="nofollow noreferrer">ESP32-01 Breakout and Development Board</a> from EzSBC.com.  It is advertised as a board specifically designed for use with batteries because of it's low current draw when in sleep.</p>

<p>As a test I loaded the basic Arduino <code>blink</code> sketch onto the board using pin 19 as the built in test LED.  When I power the board from the computer through the USB connection the LED blinks as expected, but when I connect a battery accross VIN -> GND nothing happens.</p>

<p>What am I doing wrong?</p>
 62375: <p>There is a subtle design choice in this board that took be hours to figure out.</p>

<p>According the <a href="http://www.ezsbc.com/index.php/productattachments/index/download?id=30" rel="nofollow noreferrer">connection schematic</a> the blue leg of the LS3528RGB LED is connected to <code>IO19</code> through a 1k resister (<code>R2-1</code>).  However the power leg is connected to <code>Vusb</code> <em>not</em> <code>3.3V</code> like the other RGB LED.  This means that the LED connected to IO19 is only usable when the board is connected through the micro-USB port and not when connected directly to battery.</p>

<p>This can be useful for programmatically reading whether the board is running on battery or USB. </p>
