L'Antre du Tryphon
An ESP8266 running NodeMCU can yield maximum frequency of 1.44 kHz with a duty cycle of 61%. The wave form is given below. The code used to perform this test is:
pin = 8 gpio.mode(pin, gpio.OUTPUT); while true do tmr.wdclr() gpio.write(pin, gpio.LOW) gpio.write(pin, gpio.HIGH) end
Without clearing the watch dog (tmr.wdclr), the device can yield a frequency of 1.84 kHz. Without clearing the watch dog, the device reboots after a few seconds.
Click on the picture to enlarge it.