Forgive my ignorance but I have never heard of "dry contact input" before - what does it mean?

...R

"Dry contacts" mean one is simply wiring to a set of switching contacts that contain no voltage from any other external source. A button switch is an example of a set of dry contacts, a relay is another example of having dry contacts available for the user to utilize in any way they want up to the electrical limits of the contact ratings.

Lefty

Well you need two pieces of information to estimate or calculate the duration from the battery. First is the mAH rating specification of your battery cell and second the current consumption drawn by your arduino. You do this second reading using your meter in it's current reading function (in series) not by reading the battery voltage with the meters voltage reading function.

Lefty

[what kind of resistor do i need?]

Looks like you have no current limiting resistor wired to the led. Once the applied voltage is at or above the Vf rating of the led it acts like a short circuit and will try and draw very high current which may then cause the voltage regulator to go into overcurrent protection mode.

Lefty

interesting. i didn't know that. what kind of resistor do i need? and will that fix everything? (if there's no other short circuits or any other problems not related to the schematics)

Depends on the Vf specification and the maximum continuous current rating for the led is. Given that information it's a simple ohm's law calculation to determine the proper size of the resistor required.

Lefty

greets

Can the Arduino interfere with the functioning of a circuit if you use the Arduino to measure voltage drops across switches (i.e. see if this or that switch is open/closed)? I have a device and I want to use an Arduino to detect open/closing of multiple switches. Also could shift registers be used to increase the amount of switch detectors?

If the maximum voltage across switch is 5.5vdc or less there is no problem reading it on a arduino as arduino input pins have very high input impedance so will have little or no effect on the signal. Whether to read it as a digital or analog voltage depends on the nature of the signal going through the switch. However for it to work there must be a common ground wire also run from the circuit to be measured to an arduino ground pin. You can't do it with just one wire.

Lefty

Looks like you have no current limiting resistor wired to the led. Once the applied voltage is at or above the Vf rating of the led it acts like a short circuit and will try and draw very high current which may then cause the voltage regulator to go into overcurrent protection mode.

Lefty

Time to kick the nasty habit of using linear regulator chips. Switching DC/DC regulators are just too cost effective, efficient, and versatile to not utilize these days.

http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Lefty

You can't use that external pull-down resistor on pin 0 because there is a de facto pull-up resistor already on pin 0 from the USB serial converter chip. If you wish to use a button on pin 0 just wire it from ground to pin 0 and a digitalRead LOW will mean the button is being pressed and a reading of HIGH will mean it's not being pressed. Pin 1 can use a pull-down resistor if you wish but it's simpler to just enable the internal pull-up resistor and wire the button between pin 1 and ground and have it return the same values as pin 0 would do.

Lefty

I might want to look into and research load cells or strain gauges, they are available in all sorts of ranges. They are rugged and accurate but do require good low level amplification as most are designed to be wired into a Wheatstone bridge circuit.

Lefty

E-bay junky here. 

Lefty

Hiya,
I have a Adafruit barometric pressure sensor:
http://adafruit.com/products/992
I wired a LCD up so that the sensor would print the readings onto the LCD. When I plug the 5 volts into the sensor the screen of the LCD goes dark and the arduino power light goes off. What is wrong? 

Sounds like some kind of short circuit caused by either a wiring error or a faulty module.

Lefty

We don't need any new steekin' rules. 

With that being said, instead of purchasing a larger dual output power supply that wont fit inside my device box could i run a second supply off of the AC power to run the arduino?

Yes
This power supply converts to 9VDC and is small enough to fit where my voltage regulator is. (wouldn't need it anymore)

Yes
Link is to the power supply: http://www.digikey.com/product-detail/en/VSK-S1-9U/102-2594-ND/3465374

i have attached the schematic of what the change would be.

I don't believe you can use your Uno external SRAM the way you want as the compiler will never treat it as SRAM available for directly reading and writing of variables and/or arrays. The mega1280/2560 chips do have internal hardware support for adding external SRAM and can have the compiler be able to access it directly, but perhaps only as heap memory?

Rugged Circuits is the only firm I know of that sells external SRAM modules that allows one to add such memory but again only for mega boards not 328P based boards. Here is a link that also has some example code to show you how it can make that memory available to the compiler code you write.

http://ruggedcircuits.com/html/megaram.html

Lefty

I looked up the data sheet on my power supply and even though there is 2 postive outputs and 2 negative outputs the data sheet says it only has One output.
Is that why i am seeing this problem when i have the grounds connected to the Arduinos common ground?

Yes, I'm pretty sure that is the root of your problem, that you require two "isolated" external voltage sources from your external power supply, one for the arduino source, and one for the sensor power source which uses the opposite polarity then the arduino. Also the method of wiring the output of the sensor is rather strange but if it works when you have the arduino powered by USB then it must be converting the negative voltage powered sensor such that the arduino ADC is still 'seeing' a positive variable analog voltage that it can correctly measure.

Lefty

[Is anyone else addicted to these mircorprocessors yet overwhelmed at the amount of info/ideas out there?]

I'm back and have another newb question.  I have found this program http://arduino.cc/forum/index.php/topic,14479.0.html and think it will work perfectly for my push button truck starter.  But I need "ledPin3" to come on after the "holdEvent" but I need "ledPin3" to go off after I release the button. 

Oh and I plan on changing the labels from what they are currently to ones that fit my application, ie..."ledPin3" will become "starter" but I just want to make it work first.  Thanks Scott Brown. 


Is anyone else addicted to these mircorprocessors yet overwhelmed at the amount of info/ideas out there? 

No. No one has ever stated that before in the history of this forum. 

Lefty