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1501  Using Arduino / Project Guidance / Re: Recharging batteries ... in series. on: January 10, 2013, 04:08:18 pm
I can't simply tie one battery's negative pole to the next one's positive pole because when the charging circuit kicks in, current will flow all over the place between them.  It just won't work.

That's not really true. When was the last time you charged a car battery (which has 6 cells) with a charger with 7 battery clamps?

Assuming that the battery is manufactured properly the cells should have an equal resistance between them and should charge evenly. When cells do NOT have an equal resistance or state of charge then cells with a lower voltage should charge more quickly than a cell with a higher voltage. Everything should stay in equilibrium -- although it may require longer charge times / trickle charging to do so.

Yes I do understand that it is typical with lithium polymer batteries to control the charge in each cell individually. It's just a matter the economics of the situation where a more complex / more expensive charger makes sense.
1502  Using Arduino / Project Guidance / Re: Self Leveling Deck on: January 10, 2013, 05:41:58 am
If you get your hands dirty and dig into the Multiwii code you'll find that it can be used as a camera stabilizer (set the multicopter type as "GIMBAL") for just about any board with a 3 axis accelerometer and gyroscope. As an example, this cheap multicopter board with an ITG3205 and BMA180 should be supported.
1503  Using Arduino / Sensors / Re: using an interrupt to get rpm on: January 10, 2013, 03:37:26 am
Well you're right about it being broken smiley-wink. For starters, you're never updating Input within loop().

You shouldn't be updating your RPM measurement every 20 counts. You're trying to smooth out the readings for the current RPM but you should leave that work to the PID library. If you're having problems with your optical sensing then you need to fix that or you will never get reliable control.

I would suggest that you simplify by setting Input to the time (milliseconds) between interrupts. Also adjust the value read from analogRead(setpointPin) to units that are equivalent to the milliseconds you want per revolution. Remember that the PID library tries to match the value of Input to Setpoint and the units for each variable must be equivalent.

It would also be helpful to know what range of speeds (what RPM will be typical) you're trying to achieve.
1504  Using Arduino / Motors, Mechanics, and Power / Re: Controlling and powering a heating element, thermometer, and screen. on: January 10, 2013, 02:19:52 am
You should have at least two bulbs for redundancy. Sometimes one burns out! I found that two 30W bulbs for the ~3 cubic foot incubator I built was plenty to keep the heat up, but then if it's not you can always add larger bulbs. The shell of my incubator was a plywood cabinet with 1/2" of extruded foam insulation board.

Something I would suggest watching out for is humidity control. I continually found it very difficult to keep my humidity up and if I were to rebuild my cabinet I would add some type of misting system to do that. Assuming you're building an egg incubator, especially during the hatching stage if the humidity is not high enough the chicks will get stuck in their shells.

You'll also want to add in some air circulation to keep the heat even in your incubator. Small, computer fans will do that nicely.
1505  Using Arduino / Motors, Mechanics, and Power / Re: Powering My Servo on: January 10, 2013, 01:08:34 am
With just one or two small servos like you have it's not a risk of "frying" the Uno but rather causing power fluctuations on the board that will upset the microprocessor and cause it to reset. You won't wreck anything but you might get unreliable operation.

The servo's signal pin will use a very insignificant amount of current and is not a concern.
1506  Using Arduino / Motors, Mechanics, and Power / Re: Servo and Motor Driver incompatibility on: January 10, 2013, 12:38:07 am
This sounds like a code problem. Did you include the Servo library in your code? On a non-Mega Arduino that will disable PWM on pins 9 and 10.
1507  Using Arduino / LEDs and Multiplexing / Re: Aquarium LEDS controlled with Brushless ESC From RC on: January 09, 2013, 03:55:38 pm
Using an ESC or motor driver is an unstable method with no failsafe; as soon as you teeter a little bit over the current limit of the LED you'll blow the LED. Just don't do it.
1508  Using Arduino / General Electronics / Re: Arduino UNO and low cost humidity sensors on: January 09, 2013, 01:51:46 pm
Good tutorial:
1509  Using Arduino / Project Guidance / Re: Battery Type on: January 09, 2013, 11:31:16 am
What I was looking at was the below link and thinking just dropping the voltage via a resistor.

Use a "BEC" (also called "UBEC") as Erni suggested. Definitely do not use a resistor.

The battery pack you have linked is rated at 50C meaning it can discharge 50 times its capacity (in short bursts) or 250 amps. This is way over the amperage you'd need; you can save a little money by finding one with a lower C rating.
1510  Using Arduino / LEDs and Multiplexing / Re: LEDs without the use of current limiting resistors on: January 08, 2013, 05:36:00 pm
As an aside, this is easily my favorite thread of the new year.

Not one mention of Sparkfun's place in all of this yet (OP's example was written by a Sparkfun employee).

Sparkfun did sell a no-resistor-multiplexed-led display, their 7 segment serial display. They updated it. Spot the difference smiley-wink
1511  Using Arduino / Project Guidance / Re: Battery Type on: January 08, 2013, 03:46:18 pm
What are you using now for a battery pack (link to the product?) and what is your goal for your next battery pack? I assume you're looking for more run time; detail as to how much run time you have now and how much you want is the question.
1512  Using Arduino / Microcontrollers / Re: programming attiny 85 error on: January 07, 2013, 01:44:51 pm
Pins 7, 8, and 9 output the status of ArduinoISP; use a ~500R resistor and an LED and they will flash based on the ISP status. Pin 9 is the heartbeat LED and will pulsate so you know ArduinoISP is running; that will verify that your caps are working to disable the reset.
1513  Community / Local Groups / Re: NE Iowa/SE MN/Westren WI or Des Monies IA? on: January 06, 2013, 11:04:40 pm

Liudr, what do the AX-man stores stock? Just a lot of electronic stuff?
1514  Community / Bar Sport / Re: I bought a battery on: January 06, 2013, 10:48:07 pm
Roughly you charge lead acid batteries at a rate no more than 1/10th their capacity for optimum lifetime. So your 30Ah battery would be charged at 3A. But the charge rate is not as important as avoiding discharging or 50% or leaving it sit off a charger for months at a time.

It's also worth noting that a sealed battery is charged to a different float voltage than a flooded (car) battery. Your charger offers no ability to choose the battery type; a slightly more expensive charger would.

Good reading for a similarly sized AGM battery showing how discharge level/rate affects battery life.
1515  Using Arduino / Sensors / Re: Sensing the impact of a projectile on: January 06, 2013, 09:42:39 pm
My main worry is to limit the signal going to the arduino.
With the microswitch it is easy: look for at break in the circuit.
But with the piezo, I'm afraid that I'll fry the pin with the generated voltage.

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