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Topic: Not getting enough power out of 2N3904 transistor to motors (Read 2 times) previous topic - next topic

optical_sensor_array

Ok, I lied.  I don't know why I said the transistors were wired like that, they have 9v going to collector, then emitter through the motor then to ground.  The reason I am using these transistors is because I had purchased a pack of 100 from a hobby pack so I have a lot laying around, and also as a learning process in starting with the basics and building circuits from scratch.

Either way, what I've noticed is if I send the 9v through the base of the transistor, it allows all of the collector voltage through (full power to motors), but with just the small signal from the arduino outputs, not much goes through.

And yes, the car uses 6 1.5v nimh batteries

Here's a quick sketch of the motor portion of the schematic:

dhenry

With that kind of connection, your motor is getting just 5v when it is on.

You will need a phase shifter for the upper npns.

dc42

Driving the lower transistors like that without resistors between the base and the Arduino is a good way to damage both the transistor and the Arduino.

If you have any PNP transistors, you could use the attached circuit for each side of the H-bridge. Like your existing circuit, if you accidentally set both output pins HIGH at the same time, you will short out the 9V supply and probably blow the transistors.
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optical_sensor_array


Driving the lower transistors like that without resistors between the base and the Arduino is a good way to damage both the transistor and the Arduino.


When I attached a 1k resistor (per a schematic I was using as reference) the transistor was barely getting a signal.  Who knows, maybe I've already damaged the arduino outputs, but I'm still getting a weak signal out?  In any case, it looks like ill be needing some pnps shortly.

Thanks for the schematic, I plan to eventually use PWM outputs to smooth out the speed of the motors, will this setup be suitable for that?

LarryD

The way you have it in your schematic isn't the same as how you have it wired up!

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