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Topic: Why LED works but BC547 is not Working ? (Read 8801 times)previous topic - next topic

vbnewcomer

Feb 25, 2013, 04:38 pm
Members,

Please help me out for my PIR Sensor example where i do make PIN 13 of Arduino Uno R3 HIGH when i get signal from PIR from Digital pin 2. LED works fine but when i attach BC547 with 4.7K registor to base pin of BC547, +V12 to Motor and Ground of Motor to Collector pin, and Emitter to Ground as per attached image and fritzing layout.

With same circuit, my LED get powered on but motor is not. I know i'm making something wrong but not able to find out where.

James C4S

#1
Feb 25, 2013, 04:44 pm
Why 4k7?  You probably need something smaller.

What's the measured voltage of the battery when the motor should be "0n"?
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

JimboZA

#2
Feb 25, 2013, 04:47 pm
And I think you might have the collector and emitter back to front
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vbnewcomer

#3
Feb 25, 2013, 04:56 pm
when i connect power to pin 1, nothing to Base and ground of motor to pin 3 motor works does it mean that BC547 is shorted or not working ?

xpleria

#4
Feb 25, 2013, 05:06 pmLast Edit: Feb 25, 2013, 05:09 pm by xpleria Reason: 1
Well, how did you select the base resistor?

Refer to the datasheet. Check your transistor type (A, B, C). Probably your using type B with 220 hfe approx.

Connect your motor to the 9V battery directly via multimeter and measure the current. BC547 can't handle currents greater than 100mA.

The below calculations are based on the assumption that your motor uses 70mA.
IC = 70mA
IB = IC/hfe = 70/220 = 318 uA.
VBE (sat) = 0.8V
Hence voltage across resistor is 5 - 0.8 = 4.2V
R = 4.2/318u = 13kohm
with 10% overdrive, R=R/1.1 = 12kOhm

You probably burnt your transistor. Design your amplifier before you actually try it.

vbnewcomer

#5
Feb 25, 2013, 05:16 pmLast Edit: Feb 25, 2013, 05:36 pm by vbnewcomer Reason: 1
xpleria : I think you pointed rightly, my DC 12V/200R motor is using more than 200mA as mine DMM cant measure more than 200mA so can't figureout actual current it is taking and i might have burnt my transistor as when i power CE motor works so i think it might be shorted... ( I measured it with 10A max setting and it is taking 1.75 A !!!)

Will try with another one and BC547 is B type... True... three lines written as BC, 547B, J5 E i do not understand what that lines was till you pointed out...

Thanks

dc42

#6
Feb 25, 2013, 08:16 pm
BC547 is completely the wrong transistor for switching a motor - it's rated at 100mA maximum. For switching small motors, you can use BC337 or ZTX851, with a 100 to 220 ohm base resistor. For larger motors, use a logic level N-channel mosfet instead.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

be80be

#7
Feb 25, 2013, 08:20 pm
Its not going to work the OP doesn't have the gnd tied on the arduino

dc42

#8
Feb 25, 2013, 08:26 pm

Its not going to work the OP doesn't have the gnd tied on the arduino

Good catch!
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

vbnewcomer

#9
Feb 26, 2013, 03:08 am
Actually i was trying with relay but because it was not working and DC motor from friend came handy, i instantly try with that !!! i was trying to on relay of 6VDC (Sun HOLD - RAS0610) but somehow it was not working and hence try the DC motor and was totally un-aware about Amphere it was consuming as even my wall-wart DC converter is 500mA max output !!!

So my relay 6VDC/7A with coil resistance of 103 Ohm will work with the same circuit ...?

bernir

#10
Apr 23, 2016, 12:14 am
You have to connect Arduino GND to the minus of 9v battery

sterretje

#11
Apr 23, 2016, 08:04 amLast Edit: Apr 23, 2016, 08:04 am by sterretje

Just in case people do not notice: this thread is over three years old.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

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