Show Posts
Pages: 1 ... 700 701 [702] 703 704 ... 1169
10516  Using Arduino / Installation & Troubleshooting / Re: External power supply usage? on: May 24, 2011, 08:46:18 pm
Alright, I'm using an UNO. The reset thing just has to do with the fact that I'm keeping time without an RTC. If there's a power failure setting the time again is no big deal, but I'd rather not have to set the time every single time i hook up my laptop.

There is no problem with having external power and USB power on at the same time. The boards that have an auto-voltage selector circuit will always utilize external power if it's avalible, that is it has priority over usb power. However having your arduino board reset or not is more a function of the PC software you are using and if it activates the DTR signal or not. Most arduino boards these days have the auto-reset on DTR function so if it's important that your running sketch is not reset then you might consider disabling that function and only enabling it when needing to upload a new sketch.

Lefty
10517  Using Arduino / Project Guidance / Re: Measuring Mains Voltage on: May 24, 2011, 08:26:14 pm
Quote
what's wrong with a voltage divider?

One part I don't like about using a voltage divider for directly measurement with an Arduino is that one then must have a common ground connection from the arduino to the AC neutral. Also be aware that if you want to read an analyze the AC waveform directly with an arduino, you are going to need some op-amp conditioning to offset the voltage so that it is all within a 0 to +5vdc range, the arduino cannot handle the negative portion of a AC signal.

As far as if it's intrinsicly safe to deal with direct connections to household AC power or not, it's all about the knowledge and experience level of the person asking the question. The typical snarky response around here is that if you (not aimed at you personally, just posters at random) have to ask, you most likely shouldn't be fooling with it.

You should understand that there are a awful lot of very young user that post such kinds of questions or seek help dealing with AC power. We normally have no idea what their actual age or experience level is, so it's pretty understandable that many of us discourage practices like direct wiring to AC power circuits. It's not a reflection on you, but rather a general feeling of responsibility to encourage safe practices for posters new to the world of electronics.

Lefty
10518  Using Arduino / Project Guidance / Re: get the arduino to push the button on: May 24, 2011, 08:08:48 pm
thanks for the help! Lefty, do you know a good schematic anywhere for wiring up that relay? I would still use a tip120 or some sort of transistor, no? does this circuit look good? http://www.flickr.com/photos/anachrocomputer/3242387876/in/photostream/
it's good to know that i can drive the relay with the arduino...having three wall worts for one video would be a little ridiculous...


That circuit (using a transistor to switch the relay) would work fine. However that relay I linked for you only consumes 10ma of current, so an arduino output pin can drive it directly without a transistor if you desired. If you do wish to not use a transistor then just wire one side of the relay coil to an output pin and the other side of the coil to ground. You should still use a diode like shown in the circuit, but wire the diode right across the relay coil terminals with the anode side of the diode wired to the grounded side of the relay. The two relay contact terminals of course just wire directly across the switch contacts you are controlling.

Lefty
10519  Topics / Science and Measurement / Re: can't get full range from 4mA-20mA sensor on: May 24, 2011, 08:03:09 pm
Well that wiring plan looks OK to me. Do you have a link to the sensors datasheet? Possible things you can try to troubleshoot:

Measure the current in the loop when you apply 100% humity to the sensor. If it doesn't reach 20ma, and the sensor is not at fault, then you need to either increase the loop voltage or lower the resistor value until you can reach a 20ma = 100% condition. Most loop powered sensors are designed to work with a 24vdc loop voltage and below that there are resistrictions on the total amount of loop resistance allowed (wire length + sensing resistor).

Lefty

10520  Topics / Science and Measurement / Re: can't get full range from 4mA-20mA sensor on: May 24, 2011, 05:18:33 pm
Can you draw out the complete circuit being used including the loop supply power supply and how it's wired to the arduino?

Lefty

10521  Development / Other Software Development / Re: idea for physics.h library on: May 24, 2011, 05:10:25 pm
Here is a great little free windows GUI conversion utilites that might be useful for checking out many conversion functions you might create:

http://joshmadison.com/convert-for-windows/

Lefty
10522  Using Arduino / Project Guidance / Re: get the arduino to push the button on: May 24, 2011, 05:00:57 pm
Hello,
I hope this is a simple question...
I am a visual artist and I embed digital photo frames to play videos in my sculptures. The problem is, is that no digital photo frames that I can find play video right away on start up...you always have to press a series of buttons to get the video going.
What I did in the past is just soldered onto the buttons and extended them so that you didn't have to reach into the sculpture to press the button and get the video going. But I'd like to use an Arduino to send a signal to the button to press it. So say I need to press one button, wait a few seconds and press it again, is this is simple as making a digitalOut and setting it to HIGH, delaying, set it to LOW, then setting it to HIGH and LOW again? Would it be even easier(cheaper) to just program a smaller AVR chip to do this, if I really wanted a bare bones setup? There's probably some stuff with voltage that I don't understand so anything you can help me with is much appreciated!
Thanks so much for any feedback!



Yes it is conceptually as simple as that. However because of possible voltage differences and unknown circuit details for the digital frame device, it's often simpler to have the arduino turn small relays on and off with digital commands and wire the relay contacts across the devices' switches. That way there is no need to know the voltage, current value or polarity of the frames button circuits. One relay for each switch you have to control. Here is an example of a small +5vdc relay that an arduino output pin can drive directly. http://www.allelectronics.com/make-a-store/item/RLY-541/5-VDC-SPST-N.O.-DIP-REED-RELAY/1.html
One should wire a reversed biased diode across each relay coil for transient protection.

Lefty
10523  Using Arduino / General Electronics / Re: Can I connect 22 20mA LEDs each though a 150 resistor then each to a Digital pin on: May 24, 2011, 04:49:45 pm

Will here is the gory details of current limits from the datasheet:

Quote
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
ATmega1281/2561:
1.)The sum of all IOL, for ports A0-A7, G2, C4-C7 should not exceed 100 mA.
2.)The sum of all IOL, for ports C0-C3, G0-G1, D0-D7 should not exceed 100 mA.
3.)The sum of all IOL, for ports G3-G5, B0-B7, E0-E7 should not exceed 100 mA.
4.)The sum of all IOL, for ports F0-F7 should not exceed 100 mA.
ATmega640/1280/2560:
1.)The sum of all IOL, for ports J0-J7, A0-A7, G2 should not exceed 200 mA.
2.)The sum of all IOL, for ports C0-C7, G0-G1, D0-D7, L0-L7 should not exceed 200 mA.
3.)The sum of all IOL, for ports G3-G4, B0-B7, H0-B7 should not exceed 200 mA.
4.)The sum of all IOL, for ports E0-E7, G5 should not exceed 100 mA.
5.)The sum of all IOL, for ports F0-F7, K0-K7 should not exceed 100 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
ATmega1281/2561:
1)The sum of all IOH, for ports A0-A7, G2, C4-C7 should not exceed 100 mA.
2)The sum of all IOH, for ports C0-C3, G0-G1, D0-D7 should not exceed 100 mA.
3)The sum of all IOH, for ports G3-G5, B0-B7, E0-E7 should not exceed 100 mA.
4)The sum of all IOH, for ports F0-F7 should not exceed 100 mA.
ATmega640/1280/2560:
1)The sum of all IOH, for ports J0-J7, G2, A0-A7 should not exceed 200 mA.
2)The sum of all IOH, for ports C0-C7, G0-G1, D0-D7, L0-L7 should not exceed 200 mA.


Lefty
10524  Using Arduino / General Electronics / Re: Converting Arduino PWM to Xbee Analog Input on: May 24, 2011, 02:18:06 pm
could you explain what exactly you want to do? Why wouldn't it be sufficient just to send values through the xbee?

markbee

It may be that the Xbee is a 3.3vdc device and not able to handle 5vdc signals?

Lefty
10525  Using Arduino / Project Guidance / Re: Measuring Mains Voltage on: May 24, 2011, 02:07:25 pm
Quote
My first problem is measuring mains voltage.  I have split phase 220 which means I have 110 at the plug for the freezer.

First it's important to understand what you really have avalible at your dryer outlet. Most dryers are 220vac and have a three wire plug, two hots (L1 & L2) and a safety ground, no neutral wire. You can only get (or measure) a 120vac circuit if you have the neutral wire along with either or both hot wires (L1 or L2). So only if you have a four wire dryer plug would you have the neutral wire avalible. The ground wire should never be used to allow continuous current to flow. It's designed, by code, to pass only fault currents and should not be part of a permanent measurement circuit.

So tell us what kind of circuit (3 wire or 4 wire) you actually working with and what you wish to measure. As far as voltage monitoring of any AC circuit, I would favor a transformer coupling to a lower safer voltage.

Lefty
 
10526  Using Arduino / General Electronics / Re: LM317 Help on: May 24, 2011, 12:29:29 pm
Depends what you declare "ground" to be.

Correct, we would need to know if he is using the PC supply for any other loads, or desires to.

Lefty
10527  Using Arduino / General Electronics / Re: LM317 Help on: May 24, 2011, 12:23:26 pm
Quote
Any idea on how I would get more than 12V with a PC PSU?
I assume PC supplies still have -12V outputs.
-12 to +12 is 24 volts.

Not really usable that way in a common grounded system.

Lefty
10528  Using Arduino / General Electronics / Re: Converting Arduino PWM to Xbee Analog Input on: May 24, 2011, 12:19:08 pm
Quote
I need to do RC filtering between Arduino's PWM pins and Xbee Analog input pins, otherwise the Xbee pins will be burned due to voltage mismatch.

A low pass filter will convert an arduino pwm signal to a constant analog voltage in the range of 0-5vdc depending on the duty cycle value of the pwm signal. This would not prevent 'burned due to voltage mismatch' if the Xbee cannot handle a max of 5vdc input voltage. So you may be mixing up two different requirements. Do you require a constant analog dc voltage or are you concerned about what max voltage a Xbee can safely handle? A low pass filter won't solve that latter concern by itself.

Lefty


10529  Community / Bar Sport / Re: Would anyone be interested in how to make a <$100 11*11*11 Bi-color LedCUBE? on: May 24, 2011, 12:06:07 pm
An LED cube project can be a very rewarding and challenging project. Don't underestimate the amount of labor one will require, esp for the larger cube sizes. I scratch built and programmed  a 5x5x5 blue led cube and found it quite challenging. Recommend diffused leds for best visual effect.

Lefty
10530  Using Arduino / General Electronics / Re: LM317 Help on: May 24, 2011, 12:00:55 pm
Quote
The input voltage will be 12V from a PC PSU, will the LM317 be able to give 12V output?

No, the chip has a regulator drop out voltage specification. It's dependent on how much current is being drawn from the regulator and is about 2 volts at 1 amp drop, so plan on around a 10vdc max output for the regulator if being supplied with +12vdc.

 Also be sure to add series current limiting resistors going to the base of those switching transistors.

Lefty

Pages: 1 ... 700 701 [702] 703 704 ... 1169