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Topic: Different questions regarding transistors. (Read 1 time) previous topic - next topic


Hey everyone,

So I tried this circuit: http://forum.arduino.cc/index.php/topic,52984.0.html, except instead of the laser module I have a motor, and I added a 1K resistor between the base of the transistor and the pin 9 of the Arduino. When I wire the + to 3.3V on the Arduino, the motor spins, but very slowly, and when I wire the + to 5V on the Arduino, the motor doesn't spin at all and the led pin 13 blinks. How's that?

I also tried this circuit: http://quarkstream.wordpress.com/2012/05/31/arduino-12-transistors/, except I didn't use the same transistor. I used a BR 9014, and it didn't work, for some unknown reason. Why not?

I also have a question concerning a H bridge for the Arduino. I have 2 BR 9015 (PNP?) and 2 C945 (NPN?) . I would like to know if it's possible to set up a H bridge with these 4.

Thanks in advance for your help!


There's a nice illustration here:

Note the arduino 5V regulator only serves up little current.. your motor, probably requires more than your USB port can supply.
Transistors help with a related problem (power supply differences).
Look at that image carefully and you'll see what is needed - and how the circuit should work.

Tie the grounds together.


Hey thanks for your help, so it would work with the 4 transistors I have right?


Hey thanks for your help, so it would work with the 4 transistors I have right?

Based on the datasheets (you would do well to download them, read them, and understand them), in theory these transistors are fairly complementary pairs (probably not ideal, but good enough for experimentation); your motor would have to be fairly small and only draw about 100 mA of current (at about 3 to 6V). Basically, such an h-bridge could likely power a small DC toy/hobby motor.

Something you'll need to do first is identify the pins accurately. TO-92 transistors are made by a ton of companies, and I have seen such transistors with the same part number and package type, but made by two different companies, have different pin outs (that is, the various pins for base, emitter, and collector were swapped around!).

So - identifying these leads will be your first step - there are numerous tutorials on the internet that can guide you, provided you own a multimeter (and if not - then why not? Go out and buy one - inexpensive ones can be easily obtained).

Once you know your leads and pinouts - put 1K resistors on each base of each transistor. Also be sure to hook up your flyback diodes (if you want your transistors to survive!). Make sure you take into account shoot-thru and how to prevent it (best way is to tie the bases of each opposite-corner transistor pair that controls the direction to the same pin, provided you have enough current from the pin - I personally like to use a buffer IC or another transistor in-between - that way, I won't sacrifice my Arduino's pins if something goes wrong).

So - these transistors would be alright for experimentation, at least. I would expect to potentially blow a few, but they are likely cheap devices (?) that you can probably pay a couple dollars for a handful (or - if you really know where to shop, you can easily get several hundred for the same amount of money).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

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