NPN transistor is always flickering and on

[doggy]

TL;DR

DIY circuit problem with NPN transistor.

I'm completely new in hobby electronics, and I assembled the following circuit to control a power LED over wifi using esp8266. The problem is, that it is always, on and sometimes flicker , no matter,what I send via GPIO1 port. I know that this is not an esp8266 problem, I tested my program with a simple low power LED, without the NPN TIP41C transistor. I'm sure, I do something wrong with connecting that transistor. What should i do？

 

[Tom.G]

1. Check that you have the TIP41C wired correctly, the pinout is slightly different than many. See the datasheet you linked to.
2. Temporarily short TIP4C pin 1 to pin 3. With the power ON the LED should be Off.
   2a) If it stays On, check your wiring.
   2b) If still On AND wiring is good, replace TIP41C
3. If LED goes Off with pins 1 & 3 shorted:
   3a) Verify that the ESP8266 GPIO pin is programmed/configured with a pull-down.
4. If all the above are correct, connect a 4.7k resistor between pin 1 & pin 3 of the TIP41C.

Some voltage measurements will likely be needed for further troubleshooting. I hope you have a voltmeter.

Note: There are several variations of the ESP8266 as shown by the characters after the 8266. Some have a programmable pulldown and others a programmable pullup on the GPIO pins. This MAY be a contributing factor to your problem.

Have Fun! (and let us know what you find)
Tom