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11956  Using Arduino / General Electronics / New switching regulator on it's way on: January 27, 2011, 11:50:13 pm
I couldn't pass on this little gem. Specs look pretty good. I will let you guys know what I think about it once it arrives and I have a chance to play with it. I mostly wanted something to experminate with my 'bandgap' A/D auto-calibration function and needed a way to vary Vcc power to my Arduino board by small repeatable increments. Linear voltage regulators are so 1980s  smiley-grin

 http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220648404910&ssPageName=STRK:MEWNX:IT


Lefty
11957  Using Arduino / Sensors / Re: sensors affecting one another on: January 27, 2011, 10:12:25 pm
Perhaps if you could post links to datasheets for those two sensors we might gain more insite to what might be the problem.

Lefty
11958  Using Arduino / Motors, Mechanics, and Power / Re: Looking for an electrically actuated water valve on: January 27, 2011, 10:08:11 pm
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if your dunnies are the same as ours

Is that what ya all call your crappers?  smiley

Lefty
11959  Using Arduino / Programming Questions / Re: Servo Control on: January 27, 2011, 10:00:43 pm
Quote
Thanks! It was the detach that needed more time, doh!

Your welcome.

It's really not the detach command that needs the delay, but rather the servoPan.write(pos); command needs delay after starting, to allow the servo to actually reach the new postion commanded.


Lefty

11960  Community / Website and Forum / [SOLVED] Can I attach pics into my post? on: January 27, 2011, 09:55:23 pm
I tried via the Additional Options below the test window, but got back:

Quote
The attachments upload directory is not writable. Your attachment or avatar cannot be saved.


It's a .jpg file of 45K length.

Lefty
11961  Using Arduino / Programming Questions / Re: Servo Control on: January 27, 2011, 09:38:38 pm
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Either way shouldn't the software be able to attach as needed? I saw a example somewhere but doesn't work for me. There isn't much more to the code.


Of course it would better if you posted your full sketch, my bet is that your is not allowing the servo time to reach it's new position before it performs the detach command. Servos don't move as fast as code does.  smiley

As an experiment, try adding a delay(2000) command just before you detach command and see if that doesn't tell you whats going on.
Lefty
11962  Using Arduino / Programming Questions / Re: Servo Control on: January 27, 2011, 09:24:39 pm
Quote
They do stay in position when they are off.

In the overall context of servo usage, a servo is designed to be powered continuously and have a continuous ppm control signal applied. If a servo is powered off by removing it's Vcc voltage, or by detaching in software thus removing command pulses, the servo loses all ability to respond to external mechanical forces that may be trying to move it from it's present position. As long as it has power and control signals it can generate maximum torque to overcome mechanical forces that might be trying to move the output wheel. So un-powered or detached it only offers mechanical torque resistance equal to it's internal gear train friction, higher then that and it will move to a un-commanded position.

Easy test, take a unpowered servo and grab and turn it's output wheel, does it turn? Now power the servo up and give it a fixed continuous position command. Now try and turn the output wheel. Different, no?

So in many applications where there is little mechanical force working against the servo then you can unpower when not needing a change of position. I think the average current draw of a servo a rest with no external mechanical forces is around 7ma, but that of course varies on size and design of your specific servo.

That make sense?

Lefty
11963  Using Arduino / Project Guidance / Re: Mult-Directional Rrotary Encoder w Push Button on: January 27, 2011, 09:14:54 pm
Well if you just want your basic mechanical encoder with push button monentary switch, E-bay has several:

http://shop.ebay.com/?_from=R40&_trksid=m570&_nkw=Rotary+Encoder+Switch+

Keep in mind that because their mechanical contacts and not optical or magnetic, you code will have to 'debounce' both the two encoder channels and the switch contacts. These little beasties do like to bounce their contacts.

Lefty
11964  Using Arduino / Motors, Mechanics, and Power / Re: Looking for an electrically actuated water valve on: January 27, 2011, 08:46:58 pm

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(also, yea, I realized after the fact that ball valves are either on or off, been a while since I had a hydraulics class)

No, a ball valve can be used to throttle flow anywhere from full off to full on and anywhere in between, just by the position of the handle/ball. A ball valve's main claim to fame is that it can be made to allow full flow restricted by only the piping size and line pressure. That is a 1/4" ball valve has a full 1/4" hole in the ball and therefore allows full potential flow in 1/4" piping systems. They tend to be the more expensive style of valve per size because of the precision machining required to make the ball and seat. Not sure if plastic ball values are common and if they carry a price premium also.

Lefty
11965  Using Arduino / Motors, Mechanics, and Power / Re: Logic Level MOSFET Question on: January 27, 2011, 08:38:12 pm

So many replies I think you might have a problem focusing on any given solution. Why don't you just
put off the mosfet for the moment, in that unless you have or willing to obtain a logic level mosfet
you will just be making your project more complex then it needs to be to just run your motor.

Here is the classic drawing from the Arduino playground that can be used with solenoids or motors
up to 4 amp loads using a common TIP120 NPN power transistor:

http://arduino.cc/playground/uploads/Learning/solenoid_driver.pdf

You would just wire your motor as a replacement of the solenoid L1 in the drawing.
I would use the 1k ohm base series resistor. Note that you can either turn the motor on and off
using digitalWrite() commands, or you can run the motor at variable speeds from 0-100% using
analogWrite() commands. Same circuit supports both modes of operation, you just have to
pick an output pin number that supports pwm commands if you wish that option.

Lefty
11966  Using Arduino / Programming Questions / Re: Standard Servo to Continuous Servo on: January 27, 2011, 08:21:23 pm
One other thing to keep in mind when converting a servo to continous rotation. You lose the ablility to have the motor stop at a specifc place. Your Arduino will have no feedback mechanism to determine where the servo wheel is while it's rotating or where it might stop when you issue a PWM value that stops all rotation.

Lefty
11967  Using Arduino / Motors, Mechanics, and Power / Re: Logic Level MOSFET Question on: January 27, 2011, 11:03:00 am
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Can someone explain:
VGS(th) Gate Threshold Voltage 2.0 ––– 4.0 V where VDS = VGS, ID = 250μA

According to above, I need to input 10v at gate? If this is so, how would I do that using the digital pin of arduino?

Vgs(th) is the gate voltage where the device just starts to conduct, perhaps just a few millamps. If you are using
the mosfet in a switching mode, on or off only, then you need a gate voltage that fully saturates the device on, 10vdc for your device. That of course can not be provided by directly from an Arduino output pin. You can however wire up a normal npn transistor as a switching device and switch your +12vdc battery voltage to the gate of the mosfet, but that is adding a lot of extra components and you might just be better off using just a NPN power transistor alone to switch the motor on and off via the arduino.

The series resistor between the output pin and a mosfet gate is not required by the mosfet, it will work without one, however it can be a protection device for the arduino output pin to prevent drawing too much current from the pin while trying to charge up or discharge the gate capacitance. It really depends on the specific mosfet being used as to how much gate capacitance it has and the maximum output pin current is available. All the logic level mosfets I worked with worked fine without a series gate resistor, however those recommending them have a valid point in using them. There is no reason to 'compute' this resistor, anything from 200-1k ohm should protect the output pin and still allow fast enough switching speed for your motor.

Last point, once a mosfet is fully turned on (saturated) the switched load determines how much current will flow using standard ohms law formula.

Lefty
11968  Community / Bar Sport / Re: Above the Gods on: January 27, 2011, 10:43:15 am

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I must say that great as those people were I wonder if they are above the Gods?

Only among the geeks of the world. And I don't think they come with personal lightning bolts.

Lefty
11969  Community / Bar Sport / Re: RBBB's are more expensive now, NOOOOOOOOOOO on: January 27, 2011, 10:40:44 am
Well he also has a buy it now price about $1 higher.

http://cgi.ebay.com/Anarduino-Arduino-Clone-ATmega328-Kit-NEW-/170595595809?pt=LH_DefaultDomain_0&hash=item27b84a3621

Lefty
11970  Community / Website and Forum / Re: BUG REPORT: On post of comment returns to forum, not to thread on: January 27, 2011, 10:35:01 am
I have noticed that also, and don't like it at all. This would be a good one to fix.

Lefty
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