howto operate a 12 volt dc RELAY with 89C51

[Zohaibmaroof]

Thanks dude

 

[masterleous]

I want to thanks to all those people who answered my Question

Here is my FINAL YEAR Project's video which i have finally completed with best excellence .watch it out

Ultrasonic navigation System first time made in Pakistan if i am not Wrong(Made By Zohaib) - YouTube

Well done Zohaib, your project work is excellent.

 

[gurpartap]

A 6VDC relay consume a minimum of 10 to 20 mA upon 5VDC, which is not possible to switch on directly from a microcontroller,

I have also faced same problem.I burnt my 3 NXP microcontrollers while controlling 12v relay.Does resistor bitween base and controller pin is neccessary because controller current is very minimum.when we use resistance it becomes very very small.
2.ground of supply of microcontroller should connected to 12v supply ground.
3.can I use bc337 transistor or ULN 2003 and 2803.
4.what is need of flyback diode.

 

[KerimF]

Hi,

I wish you can provide us a schematic of your circuit. Better if you name each component differently also all the nodes. Obviously the analysis could be done more accurate if you also give the values.

For instance, is your MCU pin (used for output) of open collector type (or drain) or else? (this is given on its datasheet). The one I use has open collector pins.

Kerim

 

[Qaisar Azeemi]

well done zohaib. you did really a nice work. well done.

 

[masterleous]

A 6VDC relay consume a minimum of 10 to 20 mA upon 5VDC, which is not possible to switch on directly from a microcontroller,

I have also faced same problem.I burnt my 3 NXP microcontrollers while controlling 12v relay.Does resistor bitween base and controller pin is neccessary because controller current is very minimum.when we use resistance it becomes very very small.
2.ground of supply of microcontroller should connected to 12v supply ground.
3.can I use bc337 transistor or ULN 2003 and 2803.
4.what is need of flyback diode.

:-o Too many questions in one time :-D, i'll try to answer your all questions.

1. Yes their is need to put a suitable resistor in between a transistor and microcontroller pin, this resistor produces suitable voltage drop which is required for both micro as well as transistor. For 5V we normally use transistor in between 1K to 4.7 K ohm, which is depends upon transistor, you may use 2.2K to 4.7K ohm for general purpose transistors.

2. Yes ground connections are OK for this, all supplies ground should be common.

3. for driving PCB mount normal relay, you don't need ULN Darling ton pair Transistors IC, BC337 is more 800mA, its too big but you may use it, you may also use 2N2222, BC547, 2SC945, 2SC828.

4. Its Freewheeling diode not Flyback diode, it is for consuming stored energy in Relay after powering OFF, Actually A Relay stored energy in a current form and it returns or release energy back after powering OFF or switching OFF Relay. So a Freewheeling Diode is use to consume or neutralize this energy, otherwise this energy may cuase damage to other electrical and electronics components