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1  Using Arduino / Project Guidance / Re: What is the resistor for in the circuit for the fisrt LED example on: February 18, 2011, 11:00:31 am
Hi!

Quote
Why is the resistor there?
Resistor will drop the voltage for the LED, which only requires about 2V. Arduino outputs 5V, and this would damage your LED if connected directly.

Quote
Why 560 Ohms?
Actually, you can use a smaller value. You should know the voltage drop of your LED and its current consumption, from there use Ohm's Law to compute for the resistance. For example, common LEDs have 2.1 voltage drop, 22mA current consumption. Since you need 2.1V from 5V to power this LED, you need a resistor that will drop this source:

(5V-2.1V ) / 22mA = 131.82ohms. You may use a higher resistance than this, say 150ohms. (Though I think 130ohm resistor won't hurt much)


Regards,
2  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 16, 2011, 01:03:01 pm
Hi guys!

Apparently, after 3 days of coding and mechanics preparation, the motor control circuit did not function, again. We do not know the reason, the output pin of arduino is fine, since we tried measuring the voltage and current. The motor runs when directly connected to battery, but when controlled via TIP121, it did not function the way we wanted it. Is there any problem when the current fed to the base of this darlington transistor is only about 3.5mA? The second time we tried it (as posted above), this very same amount of current did switch on the transistor. Anyone had the same problem?
3  Using Arduino / Sensors / Re: Controlling Continuous Rotation Servo on: February 12, 2011, 06:31:54 am
We tried the sketch I coded, which includes the logic of debounce, the logic seems okay for now. The sensor seems to read eight white strips on the wheel per rotation (eight 45deg marks). I estimated the time it takes for one rotation, about 2secs. So I divided it by 8, giving me 250ms. I then decided to have a 200ms debounce per "rise" output of sensor. Problem is, would the servo's rotation decrease when loaded? I hope it will not. I'll update this thread when I have tested the movement with about 2kilos of load.

Anyone experienced decrease in rotation speed of servo when loaded as opposed to not?
4  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 12, 2011, 06:24:44 am
We tried to run the sketch again using the original PWM pin from arduino. Thing is, the motor did run! We do not know the reason why it did not work the first time. Anyway, thanks to you retrolefty and DCContrarian! ^^
5  Using Arduino / Sensors / Re: Controlling Continuous Rotation Servo on: February 11, 2011, 06:09:16 pm
You should create, what it is, hysteresis(?). How should I say the thing that I can't say? Damn!

Anyways, when the first pulse says it rising, rise a flag to say it is time to wait until it reaches certain point, then don't let it hit the code again until it is going down, and after certain point, release the flag for the next pulse. You need to define those points yourself, by the curve of the components output.

Something like that, sorry, I don't know how to explain.

Cheers,
Kari
Yeah, it's fine. You did great explaining that. Actually, after I posted about this issue, I have coded another sketch that waits for a "rise", then wait for a preset interval before another "rise" can be sensed; a feature like a debounce. I think it is the same as what you explained here. I haven't tried the sketch yet, since we tried other components. Anyway, I'll post later the results. Thanks again!

may I propose to use dynamixel servos?
They can be programmed to continues rotation AND they feedback the current angle (and other data too, like torque and temperature).
Watch for i.e. the AX-12 (I am using them, so if you have more questions, just ask).
  Thanks, great suggestion. But unfortunately, we can't afford to buy another servo, not to mention the high $$$ of the servo you suggested. But its features are awesome. ^^
6  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 11, 2011, 05:56:31 pm
I would remove the Arduino from the equation.   Use the potentiometer to connect the base to the positive power supply and slowly turn the knob until the motor kicks on. Use your multimeter to find out what's happening.
  If you read the post before those, the supply is actually 11.1V, 12.6 at full. You want me to drive the base using a high resistance potentiometer? I don't have spare of that currently, but we tried using 1k pot at output pin of arduino. I'll try again.

What do you guys think of the reason here? Anyone has encountered the same problem with TIP121?

Thanks!
7  Using Arduino / Sensors / Re: Controlling Continuous Rotation Servo on: February 11, 2011, 02:29:59 pm
Sorry, doesn't have a camera. Actually the output of the sensor we are using is an analog one. Could it be possible that the arduino "sees" the "rise" multiple times during the actual rise in voltage output of the sensor?
8  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 11, 2011, 02:18:41 pm
Are you triple sure you have identified the emitter/base/collector leads of the transistor correctly? It really sounds like you might have them mixed up. Use a datasheet to confirm the leads layout and use your multimeter to test for base/emitter conduction when proper polarity of them meter leads are applied to the base/emitter junction.
I am quite sure. I do not use a component without a decent datasheet. It is usually my impression that a good documented component is the better choice; and I am not connecting a component when I am not sure of its pin configuration. ^^
Yes I am very sure that our connection is correct. It is this:

1 Base
2 Collector
3 Emitter

Pin 1 is at left when facing the transistor.
9  Using Arduino / Project Guidance / Re: circuit diagram servos... on: February 11, 2011, 08:11:22 am
What do you mean "different wire outputs on my servo"? Servos have three terminals, one for the positive supply, one for ground, and one for PWM control (usually color white or yellow).
10  Using Arduino / Sensors / Re: Controlling Continuous Rotation Servo on: February 11, 2011, 07:13:35 am
Hi again.

I tried running the sketch I coded. It simply waits for the interrupt at one pin. This interrupt waits for a RISING pulse (i.e., a white strip is sensed). Problem is, the pin seems to "sense" a number of rises. I want to sense only one RISE, and that will trigger that a 45degree mark on the wheel is sensed. What seems to be the problem?

TIA ^^
11  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 11, 2011, 04:21:12 am
Actually, we tried using potentiometer after that. 1K pot. From 1k, we lowered the resistance down that the current measures 20mA. Still, the motor won't run. We don't want to burn the pin and the tip121, thats why we ought to stop at 20mA current at base. What do you think is the reason? Plus, when we tried again to run the sketch with 1k resistor, there was no current flowing to base, giving us the impression that the transistor was broken. After 4mins, we tried again, and there's the current again at around 3mA at 1k resistance.
12  Using Arduino / Project Guidance / Re: Arduino Autonomous Vacuum Cleaner on: February 11, 2011, 01:55:08 am
I don't know what the problem is, but apparently, the motor we are using won't start. We tried directly connecting the motor to the battery, and it runs fine. We did the circuit below, and I programmed a sketch that "soft" starts and stops the motor using keypad. We tried reading the current and voltages using multimeter, and the output pin of the arduino seems to output enough power.


The readings (resistor is 1k):
arduino output pin: 5V, 3.5mA
resistor drop: 3.8V
Vbe : 1.2V

According to TIP121 datasheet:
Iceo [ Vce=40V ; Ib=0 ] = 0.5 mA
Icbo [ Vcb=80V ; Ie=0 ] = 0.2 mA
Iebo [ Vbe=5V ; Ic=0 ] = 2 mA
Vce(sat) [ Ic=3A ; Ib=12mA ] = 2.0 V
            [ Ic=5A ; Ib=20mA ] = 4.0 V
Vbe(on) [ Vce=3V ; Ic=3A ] = 2.5V

I don't know why the motor won't start.

Any ideas?
13  Using Arduino / Motors, Mechanics, and Power / Re: Rectifier Circuit with Higher Voltage on: February 08, 2011, 03:59:41 am
Wow! You explained well! It's very silly of me, I forgot about the multimeter reading only the RMS. Since the smoothed dc is the peak, then that is the very reason.

Thank you mspguy!

Consider this topic solved. ^^
14  Using Arduino / Motors, Mechanics, and Power / Rectifier Circuit with Higher Voltage on: February 08, 2011, 03:17:37 am
Hi all!

Sorry if I'm in the wrong subforum. But this one includes Power. smiley

We have created a very very simple rectifier circuit, from AC mains to 15v DC. We have a transformer with center tap on its secondary winding of 18v. We measured the output voltage AC of this transformer, without connecting anything, and from the center tap to one 18v end measures 18.6V, from center tap to the other 18v end still measures 18.6v. We want to regulate the DC using 7815. This regulator has 2V drop-out, so it is fine we use full bridge rectifier. But initially, we used Full Wave Rectifier which uses the center-tap.

The output of the regulator is indeed 15v, but when we measured the voltage before the regulator: whopping 25V ! I don't know why this happened. So we modified the circuit and used Full Wave Rectifier which does not utilize the other 18v terminal.

Still, the output of regulator measures 15v, but the voltage before it now measures: 22V !

The regulator is functioning properly, but we don't want the regulator to drop large voltage that would contribute much to heating it.

Why is this happening? Anyone had the same experience? What should we do then?

Thanks in advance!
15  Using Arduino / Sensors / Re: Controlling Continuous Rotation Servo on: February 07, 2011, 12:09:07 pm
From where you get your position information?
  What do you mean by "position information"? If you are talking about the 45deg marks, I will put strips of white color around the wheel, every 45deg. This would then "reflect" on the sensor, which I can read thru the arduino. Do you think this will be just fine?

Any other alternatives to what I am considering? ^^
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