question...question...

[louislu]

hi....i assign a P2.1 as a output pin n connected it to a base of transistor....as attached pic...the intention of doin so is to make use of tat p2.1 to control the relay through a transistor...the relay supply is +12V....i connected the collector pin of tat transistor to the ground pin of relay...but when i toggle the p2.1 everytime...the relay seems no reaction...i suspect is the output curent of microcontroller too low....measurement is bout 0.2xx miliA...any solution?

 

[flatulent]

You need to put a resistor between the uc and the bjt. This will limit the current and put less stress on the uc. You can use a darlington pair of transistors to get more current gain.

As a test, hand hold a wire between the collector and emitter of the bjt and see if the relay closes. You need a diode across the relay coil pointing towards the +12 V. This keeps inductive spikes down. Your first toggle may have damaged the transistor from this spike.

 

[power-twq]

you can connect a 4.7k resistor between the transistor's

base and mcu's 5V supply to increase drive current.

because mcu's output generally has weak high level drive

and stronger low level drive.


best regards

hi....i assign a P2.1 as a output pin n connected it to a base of transistor....as attached pic...the intention of doin so is to make use of tat p2.1 to control the relay through a transistor...the relay supply is +12V....i connected the collector pin of tat transistor to the ground pin of relay...but when i toggle the p2.1 everytime...the relay seems no reaction...i suspect is the output curent of microcontroller too low....measurement is bout 0.2xx miliA...any solution?