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1  Using Arduino / General Electronics / Re: fun projects involving TV tuner antenna on: July 17, 2014, 05:57:15 pm
Maybe pirate radio? Is that possible on these things?
2  Using Arduino / General Electronics / fun projects involving TV tuner antenna on: July 17, 2014, 04:58:05 pm
I recently got a hold of one of those old rabbit ear antennas with the circular antenna on it as well. I was wondering if there are any fun projects I can hack it into?
3  Using Arduino / Motors, Mechanics, and Power / Re: Where to buy (or how to make) a small locking mechanism for a jewely box? on: July 09, 2014, 03:37:23 pm
How strong do you need it to be ?
Not extremel strong, i suppose just strong enough so the box doesn't open and close willy-nilly. I am not extremely concerned about intruders, just strong enough not to break easily.

One option would be to find a solenoid,  where the moving part sticks out when it is unpowered,   and pulls in when it is energised.
This seems like it would take up a lot of space in the box and also consume a lot of power. Can you link to someone explaining using this.

Another option would be to get a servo which rotates a component into a slot which prevents the device opening.
This is an idea i had, but i am not sure how exactly i would implement it, also i dont know how strong these servos are and if they would make a lot of noise. Are there any demonstrations of this?

Another option would be to get one of the tiny devices where a motor turns a screw which pushes a fixed nut along the screw and use that to propel a locking rod.
I am having a really hard time picturing this. What do you mean by "turns a screw which pushes a fixed nut along the scrrew and use that to propel a locking rod"? What is a locking rod? How does this work?

The difficulty then is to arrange things so that any physical load caused by someone trying to crowbar the lid open,  doesn't get transmitted to,   and destroy,  the delicate operating mechanism.   
I am not extremely concerned about this, it isnt supposed to be a lock-box replacement, more of a cute gesture with a nifty twist for my girlfriend.

Look at this video. 

https://www.youtube.com/watch?v=CZ8WRDVgKrk

There is a bunch more,  like this.   You can build such a gadget  and then propel it with a servo or stepper motor.

This is super cool! But making one of these seems over complicated for what i am trying to do, i feel as though there are much simpler solutions. But thanks for sharing this, it is really neat!
4  Using Arduino / Motors, Mechanics, and Power / Where to buy (or how to make) a small locking mechanism for a jewely box? on: July 09, 2014, 02:54:29 pm
I want to make a project where an RFID tag locks and unlocks a small (maybe 8"x5"x5" jewelry box.
I have figured out how to make an RFID reader accept or reject a tag and have ordered the RFID reader. Now i need to work on the locking mechanism.
I was thinking that the arduino will drive a small motor that turns a lock open or closed, but i can seem to find any locks online that are small (like made for jewelry boxes) and can be driven with a motor.
Any help on buying or making a locking mechanism would be greatly appreciated!
5  Using Arduino / Sensors / Re: RFID Box Locker/Unlocker on: July 09, 2014, 11:52:07 am
Quote
Now i just need to find decent libraries for this board and learn how to program it... Apparently the documentation for this particular board is sub par.

I'm confused. Earlier you said:

Quote
.... the code i have written for my Mifare rc5222 shield?

I must have missed something.

I meant to say, hypothetically, if i write code that works on my mifare rc522 and then im done with the project and need to transfer it to a permanent space using a standalone arduino and a non-shield RFID reader/writer, how do i know my code will still work if i don't use the same reader/writer?

I answered my own question through some more research, and the answer is that it simply won't work ( i believe) as each RFID reader/writer chip uses a different protocol for sending/receiving data i believe. Correct me if i am incorrect.
6  Using Arduino / Sensors / Re: RFID Box Locker/Unlocker on: July 09, 2014, 12:24:43 am
My mistake! You didn't say, and I didn't ask and I should have. I assumed 125kHz RFID tags. Forget that link.

You did mean Mifare RC522, correct? Hard to beat $5.20 each. On Amazon with free shipping, or at Electrodragon (never ordered from them):

http://www.electrodragon.com/product/mifare-rc522-rfid-card-readerdetector-ic-card/

That card uses the NXP MFRC522 chip:

http://www.nxp.com/documents/data_sheet/MFRC522.pdf

http://www.nxp.com/products/interface_and_connectivity/nfc_contactless_reader_ics/series/MFRC522.html

The chip alone is available from Digikey for over $6 each, not dropping appreciably until you get into the thousands. Cheaper just to source the board above.

http://www.digikey.com/product-search/en?mpart=MFRC52202HN1%2C151&vendor=568

Thanks!

Now i just need to find decent libraries for this board and learn how to program it... Apparently the documentation for this particular board is sub par.
7  Using Arduino / Project Guidance / Mifare RC522 RFID reader/writer library and tutorials? on: July 08, 2014, 10:32:00 pm
I am new to android and am planning out my first real project: A box that unlocks when you put a specific RFID tag near.

I made the mistake of ordering an RFID reader/writer without looking up documentation on it before hand. The one i ordered is the Mifare RC522 on ebay here. It is on its way but i currently am looking up libraries and tutorials for it and finding that there is not very good documentation on it. But luckily i am not the only one to try and use this RFID reader/writer.

I have found plenty of posts on this forums on the RC522 but all the threads seem to end without any resolution how to get the thing up and running. This is the most useful one i have found.

I have found a page that links to a library for it which even includes examples (albeit not very extensive, it doesnt even have  a "write to card" example). I have found an updated version of these libraries, see the edits.

I was wondering if this is the commonly used library for it and if anyone has any experience with it or programming the RC522 (with any library in general).

EDIT: After looking some more i have also found a library titled MFRC522.h and MRFC522.cpp that seems to be created by the same person that made the RFID.h and RFID.cpp from the library i linked above (the one from electrodragon). I dont know which to use, but im seeing videos of each... which one is newer/updated more recently? which one is better?
Double Edit: After some more research i have found that the MFRC522.cpp and .h are updated versions that have more features and less bugs. The owner changed the name to specify that it was more specific to the RC522.

8  Using Arduino / Project Guidance / Re: Arduino RFID lock using new Uno and MFRC522 on: July 08, 2014, 09:43:26 pm
Hello!

I just ordered a Mifare RC522 RFID Reader/writer, i didn't realize how poorly the documentation/libraries on this were. I have found some github pages that have the entire library, like the one here. But it makes no sense to me (it is long and hard to read, and also in chinese partly.

Is the RFID_master.zip library the same as this one? Or is it different? And does it work properly on the RC522?

I was wondering if you managed to get this reader to work and if so would you be kind enough to give me a simple tutorial  on the basics of reading/writing RFID tags?

Thanks a ton!
9  Using Arduino / Sensors / Re: RFID Box Locker/Unlocker on: July 08, 2014, 07:55:30 pm
Sure, the EM-18 or the ID-12 module, but they aren't cheap. Or there is even a circuit for an RFID reader you can build yourself using a couple of sections of a quad LM324 Op Amp and a few more parts. You'll have to do some work building it and wind a coil, but should be pretty cheap. The LM358 is a dual Op Amp version of the LM324. Let me look that up, it is here on the Arduino.cc site:

http://playground.arduino.cc/Main/DIYRFIDReader

I would not be surprised if this weren't essentially the same as above but with the 2nd IC being an interface chip:

http://www.amazon.com/Asiawill%C2%AE-125Khz-Reader-Control-Arduino/dp/B00HFX9NSA/ref=sr_1_21?ie=UTF8&qid=1404857328&sr=8-21&keywords=rfid+reader+125khz

No, it can't read two at once. You'd have to have the tags separated by at least a short distance, and kind of sweep them past the reader. Otherwise, either the closest will only be read, or neither will be read as they interfere with each other. Passive tags don't have any anti-collision in them.


I am a little confused because that page you links walks through creating your own RFID reader/writer, but then how do i know it will be compatible with the code i have written for my Mifare rc5222 shield?
10  Using Arduino / Sensors / Re: RFID Box Locker/Unlocker on: July 08, 2014, 01:47:27 pm
The Arduino is really just a breakout board for an Atmel AVR microcontroller, that includes a few things to make it simpler to use. A USB to serial TTL chip, voltage regulator, clock crystal, reset button.

Several use the '328, you can buy them with the Arduino bootloader already installed and connect a USB to serial TTL temporarily to program it.

There are a lot of places to buy RFID interfaces suited to Arduinos. DX.com, Seeedstudio.com, Sparkfun.com, Amazon.com, etc.

Have you searched for "rfid arduino"? There are a lot of projects out there. Some better than others.

after some research i have answered a lot of my questions, except one still lingers. Just as you can make a standalone or "breadboard" arduino to control the project once i am finished with it for good, how do i connect an RFID reader/writer without using up the shield? Just as the arduino is basically a breakout board for the Atmel AVR isn't the RFID arduino shield just a breakout for an RFID reader/writer? Do they also make chips that can be connected to standalone arduinos so i dont have to use up the shield?

Another question that i have is whether or not its possible to detect two separate RFID tags at the same time? Lets say i wanted to make a box that only opens if two different tags are present near the lock on the box at the same time, is that possible? Or will i run into an issue where the arduino identifies one and then when trying to read the other it accidentally reads the first one again?
11  Using Arduino / Sensors / RFID Box Locker/Unlocker on: July 07, 2014, 06:30:55 pm
I am relatively new to arduino and i want to build a box that has a lock on it that unlocks from within when an RFID tag is placed near it. This box would not be very large and the lock wouldn't be super heavy duty (think something sort of like a lock you keep on a diary).

I have never worked with RFID before but i assume it is the correct thing to use for this (i dont know much about near field communication, and bluetooth requires a lot more coding i think that for what is necessary).

I don't exactly know how to get started though, what would i have to buy to get the arduino to work with RFIDs? And how do i get the arduino to interface with a lock? Where is a good place to buy parts for RFID stuff and instructions/tutorials on assembly?

One question i have is, when my project is finished, do i have to give up an arduino to keep the project? I hear there is a way to burn the program onto a chip and somehow connect its outputs so that instead of using up an arduino ever time you finish a project and want to keep it you just have to buy a chip (or a chip and some other components) and solder those together and burn the device. Is there any articles i can read on how to do this? And how would i connect the RFID stuff to this chip?
12  Using Arduino / Motors, Mechanics, and Power / Re: Driving two or three stepper motors? on: July 02, 2014, 08:30:09 pm
Stay away from the ULN2003, it is worse than the L298 in that regard. Both are linear H bridge (ie, you control current by controlling voltage), slow, and hot. And they require that you provide 1-2-3-4 drive signals, whereas chips like the A4988 are chopper drivers that only require Step and Direction signals.

Chopper driver means it is a switch mode current regulator. So using a much higher voltage to drive it means current in each coil ramps up more quickly, which means more torque at higher speed.

With the ULN2003 or L298, current ramps up slowly and so torque drops off drastically with speed.

Thanks for the info!

Can anyone recommend me some good drivers? The EasyDriver and BigEasyDriver are kind of expensive... Or is that normal for good stepper drivers that only require Step and Direction like these
13  Using Arduino / Motors, Mechanics, and Power / Re: Driving two or three stepper motors? on: July 02, 2014, 05:14:30 pm
By probably not, he means probably not...

Steppers are by their nature a start stop thing. Microstepping can help reduce that. I've not found small steppers to be very loud unless you have problems with mechanical resonance. And if you do find resonances, you'll want to fix them because they often cause problems like missed steps and artifacts in cut surfaces.

I was asking because my statment was I hope they are less noisy, and he responded with probably not making me think they would be very noisy. But I thought he may have confused my statement with I hope mine aren't as noisy, in which probably not would mean "they probably won't be as noisy"

I think I just need to get into the fray and buy some motors and try them out.

Can someone explain why the uln2003 driver (which a lot of these cheap steppers on eBay come with, requires so many more input pins than the easy driver I see on sptocusee, Is it much more complicates to use or should I stay away from it like the L298
14  Using Arduino / Motors, Mechanics, and Power / Re: Driving two or three stepper motors? on: July 02, 2014, 04:03:48 pm
If you want a stepping motor to run at the fastest speed you have to ramp up the pulse or step frequency. If you don't, and try to run fast from a standing start it will miss steps or not move at all. The same is true for stopping, stop the pulses dead and it will over shoot by a few steps. This will throw off the positional accuracy of the motor.
Got it, so I I should probably use accelstepper to avoid over/under stepping.

Quote
i hope my stepper motors are much more silent.
Probably not, although motor noise depends on the speed it is running and if it hits any mechanical resonances of what it is connected to.

By "probably not" do you mean my steppers will be noisy?
15  Using Arduino / Motors, Mechanics, and Power / Re: Driving two or three stepper motors? on: July 02, 2014, 01:17:45 pm
You should produce a brief low high low pulse to cause a step. The duration high needs to be only 10 microseconds or so.

Yes the drivers have the electronics to supply current to the motors.

The L298 is a h-bridge that is really intended for regular DC motors and has no ability to limit current or to move the motor in microsteps.

You vary the speed by varying the time between step pulses.

The following code shows (in a very simple way) how to control a motor. It probably needs a lot of modification to make it into anything more than a demo.

Instead of writing this sort of code yourself you could use the AccelStepper library - especially if you need an easy way to accelerate and decelerate your motors.

Code:
// testing a stepper motor with a Pololu A4988 driver board or equivalent
// on an Uno the onboard led will flash with each step
// as posted on Arduino Forum at http://forum.arduino.cc/index.php?topic=208905.0

byte directionPin = 9;
byte stepPin = 8;
int numberOfSteps = 100;
byte ledPin = 13;
int pulseWidthMicros = 20;  // microseconds
int millisbetweenSteps = 25; // milliseconds


void setup()
{

  Serial.begin(9600);
  Serial.println("Starting StepperTest");
  digitalWrite(ledPin, LOW);
  
  delay(2000);

  pinMode(directionPin, OUTPUT);
  pinMode(stepPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  
 
  digitalWrite(directionPin, HIGH);
  for(int n = 0; n < numberOfSteps; n++) {
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(pulseWidthMicros);
    digitalWrite(stepPin, LOW);
    
    delay(millisbetweenSteps);
    
    digitalWrite(ledPin, !digitalRead(ledPin));
  }
  
  delay(3000);
  

  digitalWrite(directionPin, LOW);
  for(int n = 0; n < numberOfSteps; n++) {
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(pulseWidthMicros);
    digitalWrite(stepPin, LOW);
    
    delay(millisbetweenSteps);
    
    digitalWrite(ledPin, !digitalRead(ledPin));
  }
  
}

void loop()
{

}

...R

Thanks so much for this information!

What is the AccelStepper library? Why would i use it to accelerate and decelerate my motors rather than just stepping or not stepping? It seems to me like it has impulsive movement that doesn't require acceleration.


BTW that gantry in the video doesn't have stepper motors, its using small gear motors
and encoders - ie its driven by servo motors.

I thought it looked funny, anyway the concept and design i want is very similar.

 It is also very very loud, i hope my stepper motors are much more silent.  What determines how loud the stepper motors are? Are higher holding torque motors typically much louder? I would like to reduce the noise of the motors as much as possible.
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