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1276  Using Arduino / General Electronics / Re: Panelizing EAGLE files? on: December 07, 2012, 09:46:44 pm
You can edit the .cam file with a text editor. I'd go through an explanation of how to add another layer (section) but it's pretty self-explanatory.
1277  Using Arduino / Motors, Mechanics, and Power / Re: Motor choice and coupling on: December 07, 2012, 10:59:42 am
This dispenser looks like it will work if you turn the handle back and forth and not necessarily in a continuous rotation. Assuming that's true then an RC servo would be perfect for it; the servo could be mounted on the side of the dispenser with a couple pull rods on the top/bottom of the handle.
1278  Using Arduino / LEDs and Multiplexing / Re: Require assistance with LED Hula Hoop wiring, Seeeduino film, info inside... on: December 06, 2012, 03:52:41 am
shiftOut is software SPI. Simpler to use IMHO.

Any pins can be used with shiftOut.
1279  Using Arduino / General Electronics / Re: How to calculate torque rating for motors? on: December 05, 2012, 09:50:10 pm
It will take very little power to drive the robot on a flat surface, so you need to concern yourself with the maximum thrust you will get. This will be either how much mass you can PUSH with your robot or how steep an INCLINE you can climb.

I'd make a minor nitpick here: with a tracked/skidsteer robot there's a lot more friction to deal with when you're turning. Extremely hard to calculate how much power that requires though, especially with surfaces of varying friction.
1280  Using Arduino / General Electronics / Re: How to calculate torque rating for motors? on: December 05, 2012, 01:28:42 am
You may want to re-think having a motor per wheel with tank treads; if the motors aren't perfectly synced and moving at the -exact- same speed, you will throw the tread (and/or cause problems for the motors/gear-train). Instead, use only a single motor per tread (just like tanks and bulldozers do).

The Rover 5 has four wheel motors and no issues there. I'm a little suspicious how that affects overall battery efficiency though with twice as much gear friction.

The Rover 5 weighs 2.5lbs without batteries so probably a good starting point for you, zharvey. Each motor is 18 watts (7.2V * 2.5A) so as long as you can match that wattage at the RPM you need you should get a good 'bot running.
1281  Using Arduino / LEDs and Multiplexing / Re: Require assistance with LED Hula Hoop wiring, Seeeduino film, info inside... on: December 02, 2012, 11:41:12 am
When you connect batteries through the "BAT" plug the maximum power you can draw from them is 150ma (page 5 of the PDF). This will be much too little to power your LED strip. What you'll probably want to do is use one of your three batteries to power the film and the other two, in parallel, to power the LED strip.

To do this you'd connect the two batteries to 5V/GND on the LED strip. Then also add a ground wire between GND on the strip and the film (the strip and LEDs need to agree on a 0V reference).

1282  Using Arduino / LEDs and Multiplexing / Re: Require assistance with LED Hula Hoop wiring, Seeeduino film, info inside... on: December 01, 2012, 11:59:12 am
Sorry, I misunderstood your question. I'm only familiar with using a sleep timer and just assumed you'd be checking the buttons every X seconds to see if it's time to wake up.

http://arduino.cc/playground/Learning/ArduinoSleepCode

You can use pin D2 or D3 for this which is shown in the I2C block on the film.
1283  Community / Bar Sport / Re: Christmas List on: December 01, 2012, 02:04:07 am
I guess the hardest part is becoming a professor in the first place.

It's not that hard, you just have to fail in the real world.

 smiley-twist
1284  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.
1285  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.
1286  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.
1287  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.
1288  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.
1289  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.
1290  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.
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