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1276  Using Arduino / General Electronics / Re: Constant current power supplies on: December 01, 2012, 01:23:10 am
The ones I have supply a constant 350ma until the load resistance drops enough to cause it to shut down.  On the high side, they max out at a little over 11V and don't go any higher.  Carefully hooking it to the VIN on an arduino (UNO), they seem to work fine.  The problems may come when the combination of arduino and other devices need more than the 350ma and the thing shuts down.

But isn't that an important issue? These LED drivers are sensitive to the load they're driving; too little load and they shut off, too much load and they shut off. Only under fairly specific circumstances would you have a circuit that could keep that constant load.
1277  Using Arduino / LEDs and Multiplexing / Re: Require assistance with LED Hula Hoop wiring, Seeeduino film, info inside... on: December 01, 2012, 01:10:42 am
For hardware SPI you need pin D11 (MOSI, aka "Master Out Slave In") which connects to "DI" ("Data In") on the LED strip and D13 (SCK "Serial ClocK") to connect to "CI" ("Clock In"). These are shown within the "SPI" block on the film. Yes, it's just like the Pro Mini -- the film uses a pin-compatible ATMega168.

Where you wire the switch, the LT/RT/DN/UP/CT pins, is non-critical. There's an open group on the film D5-D9 that would be fine.

The only way to be certain your chip is sleeping is by putting a multimeter on its power line and watching the current.
1278  Using Arduino / General Electronics / Re: Homemade button to test how hard it was hit on: November 29, 2012, 01:03:47 pm
Here's my take (see image below, which is a side view):

Three strips of spring steel ("shim stock" or "feeler gauge stock", etc) cantilevered with spacers between them. Piano key is attached to the top strip.

When the key is depressed contact will be made with the middle strip of metal (which is attached to a digital pin) registering a digital high. When the key is depressed farther both strips will contact the bottom strip and ground out registering a digital low. The time between the high and low is the velocity.

Of course there are resistances needed here -- ~5K between each middle strip and the Arduino and ~500R between the 5V and GND strip. The top strip should be pretty thick (for durability) and the middle strip should be very close to the top strip. You might want to put a bend in the middle strip near the end so it contacts the bottom strip (which could be a contact sheet for all the keys) more easily.
1279  Using Arduino / General Electronics / Re: Simple solar charging a standalone ATMega device on: November 29, 2012, 12:12:19 pm
The simplest way to prevent overcharge is to use a zener diode. The charged voltage for an NiMH cell is 1.4V, so you want a zener voltage of (1.4V * 4) = 5.6V to prevent overcharge. You can use multiple zeners in series to get the total voltage you need.

Generally speaking batteries should not be charged at a rate of more than 1/10th their capacity. For your 700mah cells that's 70ma, and you're charging at 90ma max. I figure that's close enough, and in practice you won't get that much current anyway.

An ATMega running at 5V should be fine pulling power, unregulated, directly from your batteries. However, you should use an analog pin to read the battery voltage and "sleep" your bot when the batteries run low. The Narcoleptic library makes this pretty simple, but Google can help you find other examples.

Finally, like Rob mentions, there are certainly more efficient ways of doing all this (google "MPPT" for starters). I'm going from the assumption that you're trying to keep it simple/cheap and the value of the components you have at risk is low.
1280  Using Arduino / Motors, Mechanics, and Power / Re: Power/ Motors on: November 29, 2012, 11:20:29 am
You probably won't "smoke" the Arduino, but due to the power hungry nature of the motors/servos you're most likely to cause power fluctuations that will cause the Arduino to reset or make your analog readings go nutty.

This mosfet tutorial shows how to connect external power for your motor/transistor. Assuming the external power is 5V then the servo can also take power from it; connect the red and black wires to the power source and the signal line (white or orange) stays connected to the Arduino.

There should always be a ground connection between the Arduino and any external power supply.
1281  Community / Bar Sport / Re: 8) - Batteries V Capacitors? Which will win? on: November 28, 2012, 11:13:20 pm
  I'm betting on batteries, unless they ever do release the hidden patent the energy companies are secretly sitting on for the FLUX capacitor, then it will be back to the future for sure.  smiley-wink

That was released a long time ago.
1282  Using Arduino / Project Guidance / Re: Live tracking weight changes on: November 28, 2012, 10:47:59 pm
Get a digital bathroom scale and disassemble/reassemble it enough until it fits your water cooler nicely. Then either hack into the onboard electronics (sometimes the amplified reading from the load cell is available) or replace those electronics with an instrumentation amp. If you need more then the 10bit accuracy provided by the Arduino's ADC then you'll also need a different ADC to go with it.
1283  Using Arduino / Motors, Mechanics, and Power / Re: Need to build 2 amp multi output (5s volts,12s volts) power supply on: November 27, 2012, 09:11:03 pm
You seem to be on a budget; any chance you could find an old computer power supply?
1284  Using Arduino / Motors, Mechanics, and Power / Re: Bi-directional tube motor with 4 Relay Module on: November 27, 2012, 09:02:33 pm
Yes, your relay wiring is as I described. I'm still not clear on those four motor wires though so I'm leaving that to your discretion; I'm assuming that it's some type of AC motor and I'm not knowledgeable enough in AC motors to offer advice that could blow up someone else's stuff smiley-wink

Your relay module should be fine for this task. The critical thing to look out for is the amperage of the relays (which, as an aside, don't care if it's AC or DC current so long as you stay under the limits printed on the relay). Your board shows 10A relays and that should be more than plenty for a motor lifting this light of a load. Also be aware that your relay board is capable of optical isolation -- without a jumper between the JD-VCC pin and VCC pin it's expected that you have a second 5V power supply providing power to JD-VCC and GND and the Arduino's GND pin is not connected. Again, the link to the wiki I posted above explains this.
1285  Using Arduino / Sensors / Re: Can anybody identify this sensor? on: November 27, 2012, 06:56:33 pm

Basically, rain on the windshield will cause some form of reflection of the IR light back to the sensor.

You would still need to do a lot of work in characterizing the intermittent nature of the reflections of raindrops vs. driving under a tree, bug on the windshield, etc.
1286  Using Arduino / Project Guidance / Re: How to execute a function for "t" time without delay + using external interrupt on: November 27, 2012, 09:27:27 am
Just FYI:

#include <Time.h>
#include <TimeAlarms.h>

void setup() {
  Serial.println("Waiting for command");
AlarmID_t temptimer;
void loop() {
  // this is where the "polling" occurs
      case '1':
      // start recording?
      temptimer = Alarm.timerRepeat(1, Tempfunct);
      case '2':
      // stop recording?
      Serial.println(" : unknown command!");

// function to be called
void Tempfunct() {
   // do whatever reading

This is perhaps kinda heavy for what you appear to be doing (should use the "blink without delay" method), but just wanted to followup.

Also, TimeAlarms.cpp needs to be updated for Arduino 1.0.

#include <WProgram.h>

#if ARDUINO >= 100
#include <Arduino.h>
#include <WProgram.h>
1287  Using Arduino / Motors, Mechanics, and Power / Re: Bi-directional tube motor with 4 Relay Module on: November 27, 2012, 08:50:02 am
I have no idea what a "tube motor" is so I'm assuming that you understand the pinout there and have the power connections right.

Looking at how you have your relays wired, you have the potential to create a short circuit if both relays are energized. That's not a good idea unless you're the type of person that never writes software bugs and never has a hardware failure.

The + from your main power should go to the common of the first relay, the NO output of that first relay to the common of the second relay, and then the NC and NO of that second relay should go to 3 and 4 of the motor. This way the first relay controls power on/off and the second relay controls direction.

Terry's wiki on relay boards does a great job explaining how to hook these things up.
1288  Using Arduino / Project Guidance / Re: Controlling the computers mouse on: November 27, 2012, 08:36:17 am
To do this you would want to write a program (on the PC) to listen for commands on the serial port from the Arduino and control the mouse. You would need to look into available libraries for this for whatever OS and whatever programming language you're using. The InterfacingWithSoftware page provides a large number of examples for various programming languages.

On the other hand, if you're just trying to build a sort of Arduino mouse then my answer stinks and you should follow HazardsMind's link. I'm assuming you still want to be able to communicate that analog reading to the PC.
1289  Using Arduino / Project Guidance / Re: How to execute a function for "t" time without delay + using external interrupt on: November 27, 2012, 08:25:09 am
Look in the example for the "TimeAlarms" addition in the []Time[/url] library.

You topic subject mentions "+ using external interrupt"; I assume you meant for the timing only or is there something else you were trying to accomplish?
1290  Using Arduino / Project Guidance / Re: Plug it in a Wall and Use Bluetooth to Move Mountains on: November 27, 2012, 08:11:23 am
Just explain exactly what it is you're trying to accomplish. Don't make it into some kind of mystery -- you're not going to get a good answer.
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