On: Saving power on an ESP8266 web server using delays

[dekhn]

I dunno if you want to use a simple circuit; but, you can use a voltmeter in series ampmeter mode. However, I just use one of these: https://www.amazon.com/gp/product/B00FPU6G4E which has the advantage of being able to tune the voltage and current to be either constant current or voltage.