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1  Using Arduino / Motors, Mechanics, and Power / Re: Can I Connect a DC Motor to the Transistor's Emitter? on: February 12, 2013, 02:25:29 pm
Thanks a lot. I don't have any specific reason why I need to connect the motor to the emitter (instead of the collector). I was curious whether or not it would work. I didn't realize that there would be such a big drop in voltage from the collector to the emitter?
2  Using Arduino / Motors, Mechanics, and Power / Re: Can I Connect a DC Motor to the Transistor's Emitter? on: February 12, 2013, 12:20:37 pm
Thank you for the reply. Sorry, I don't understand why the motor would only receive 2.8V? The motor is being powered by a battery (external power source). I understand that if I put a resistor between the Arduino output pin and the base lead (of the transistor) then only 2.8V may reach the base, but that shouldn't impact how much voltage reaches the motor, right? I was under the impression that the transistor can drive a larger load (from collector to emitter to motor) using a small load (Arduino output pin to resistor to base lead of the transistor).
3  Using Arduino / Motors, Mechanics, and Power / Can I Connect a DC Motor to the Transistor's Emitter? on: February 12, 2013, 02:44:07 am
Most (all?) tutorials on driving a DC motor (with an Arduino) connect the motor between the power source (battery) and the transistor's collector pin. The transistor's base pin is connected to an Arduino output pin and the emitter is usually connected to Ground. There is also a diode that is connected in parrallel to the collector and emitter of the transistor. Something like this (without the diode):

Code:

  Battery (+) --------> Motor ----> Collector Pin
     |                                 Base Pin <------ Pin 9
     | (-)                            Emitter Pin ----> GND
    GND                                   


My question is: Can I connect the motor to the Emitter Pin and then to GND? In other words, the Battery connect to the Collector Pin. When the base is activated, current will flow from the collector to the emitter into the motor. Is this sound?

Thanks.
4  Using Arduino / Motors, Mechanics, and Power / Do I need a motor shield? on: February 06, 2013, 03:53:11 pm
Sorry to ask such a beginner's question, but I can't figure if I need to purchase a motor shield or not to drive a simple robot or can I get by using 1 or 2 H-bridges?

Currently, I'm able to drive motors with my Arduino Uno using an H-bridge as described here: http://itp.nyu.edu/physcomp/Labs/DCMotorControl. In this particular case, there is one H-bridge which can drive up to 2 motors but I assume I can also use a second H-bridge to connect two more motors (4 in all for a 4WD robot)? Also it looks like I can connect an external power supply with a H-bridge. So then what is the main advantage(s) of buying and using a motor shield which seems to cost a lot more than 2 H-bridges? Thanks!
5  Using Arduino / Sensors / Re: Read voltage drop from photoresister without a second resistor? on: January 17, 2013, 02:16:06 pm
Thanks! That makes sense.
6  Using Arduino / Sensors / Read voltage drop from photoresister without a second resistor? on: January 17, 2013, 01:30:35 pm
I am  starting to play with my Arduino Uno and have a question about hooking a photoresistor to my Uno. Most tutorials connect the photoresistor like this using a second resistor:

Code:
+5V --> PhotoResistor --> . --> 10K --> Ground
                          |
                        Pin X
 

I think this technique is called a "voltage divider" and I understand how it can be used to read the variable voltage drop that occurs from the PhotoResistor.

My question is why can't I just measure the drop without the 10K resistor? In other words, would the following work (where we read the voltage drop from Pin X)?

Code:
+5V --> PhotoResistor --> . --> Ground
                          |
                        Pin X

Thanks a lot!
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