Help with motion sensor and motor DC

[joanmasuka]

Hi all,

I have designed a very simple circuit gathering other projects I found in internet.
Im completely new to electronics and Im just trying to learn, so I may do very basic mistakes.
so here is the scheme I designed:



Everythings runs correctly but the motor would never turn on. So Im assuming Im not putting enough current to it, but I though by using the transistor I would allow the 6V to reach the motor.

Thanks a lot!

 

[Arouse1973]

How much current does the motor draw? What transistor are you using? You may need to lower the base resistor value.
Adam

 

[joanmasuka]

Thanks for the super fast answer.
Yes I changed the resistor to 470 and it just works fine.

I dont know if 470 is ideal but it is the only one I have here to try out.

thanks a lot!

 

[Minder]

What is the nature of the sensor?, some are open collector ouputs (NPN or PNP) If so you would need a pull-up (or down) resistor.
M.

 

[joanmasuka]

it is a NPN, so do I need more resistor or less?
and you want to tell why I would appreciate, so I can learn something. if not is ok too, i will look in the internet.
thanks a lot

 

[Arouse1973]

What is the name of the transistor? Show us a picture if you are not sure.
Adam

 

[joanmasuka]

Yes, is a PN2222A W35

 

[Minder]

it is a NPN, so do I need more resistor or less?
and you want to tell why I would appreciate, so I can learn something. if not is ok too, i will look in the internet.
thanks a lot

But is it open collector?
If open the 10k resistor from sensor collector to +ve and a 100ohm from output to Base.
M.

 

[joanmasuka]

The transstor is a NPN named NP222A W35, is all I know.
but dont worry, at least now works, I think I can look in other forums and learn a little bit more before asking very stupid questions.

thanks a lot guys!

 

[Minder]

When you use a sensor, you need to know the nature of the output, i.e. open collector? NPN? PNP?
If the device you are feeding to in this case a 2n2222 does not provide it, you have to supply it.
An example of O.Coll, . NPN.
M.

 

[BobK]

If it works with the 470Ω resistor, then it is likely a push-pull output. It would not work if it was open collector.

To know what resistor to choose you need to know how much current motor takes and how much voltage the sensor outputs.

Let's say the voltage output is 5V and the current drawn by the motor is 200mA.

Then, as a rule of thumb, to saturate the transistor (i.e. get the lowest voltage drop across it) you use a base current which is 1/10th of the collector current. With a high gain transistor like the PN2222 you can probably get by with half that. So 1/20th of the 200 mA current gives us 10mA.

The base to emitter junction will drop approximately 0.7V so, that leave 4.3V across the base resistor. Use Ohms law to determine what resistor will drop 4.3V at 10mA

V = I * R
4.3 = 0.010 * R
4.3 / 0.010 = R
430 = R

So your second guess was quite good! It should have the transistor pretty well saturated, dropping maybe 0.3V. You can test this with a multimeter and let us know what you read.

Bob

 

[joanmasuka]

ok. thanks a lot for all the answers.
now I need to study some of these answers, but I think I have enough info to get going and understand whats going on.
Also I need to buy a multimeter. As soon as I get it I will test what I get.

thanks!!

 

[hevans1944]

Also I need to buy a multimeter.

Yeah, a multimeter is a very handy tool to have on hand when experimenting with electronics. Do you need any help in selecting a particular multimeter?

 

[joanmasuka]

Well, my idea was to look into amazon or ebay for the ultimeter, maybe read some reviews, etc...
so if you have some in mind, would be very appreciate it.

thanks al lot

 

[hevans1944]

Well, it depends on how serious you are. I plan to replace my venerable B&K Model 2890A with the newer model 393, available for about $200 at various places on the Internet. The older model works just fine and it has never given me any trouble, but the newer version has more counts (60000), a type K thermo-couple jack, and a USB interface so I can control and record readings on a PC. What's not to like? This would be my third or fourth high-resolution meter from B&K and I have been happy with all of them. Fluke has some really nice multimeters too, but I think I get more bang for the buck from B&K Precision. Only problem is, B&K constantly upgrades their product line, so if I order one now it will probably be "obsolete" next year (or sooner).

You can get a much less expensive multimeter on line or at a big box store. It all depends on what you want a multimeter to do for you, and how serious you are about pursuing electronics as a hobby. I'm a pretty serious kind of guy when it comes to owning test equipment, and in the last thirty years or so it has become much less expensive. What used to be laboratory equipment that cost big bux is now available for use in the field at what I consider reasonable prices.