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1501  Using Arduino / Project Guidance / Re: PWM control of many LED's from arduino on: December 27, 2012, 02:30:59 am
Could I not just use a big resistor to current limit too the 3 x 1w LEDs, and chuck out the driver circuit?

Yes, but you don't want to. Looking at the "wide angle" bulb linked earlier, it's only driving the LED with 50% efficiency. A proper driver will do much better than that. Also, the high wattage resistors required are pretty expensive themselves, and then you also have the problem of them getting freakishly hot.

The drivers in your bulbs might have a PWM option that is not being used, but again only a look at the IC in question would provide the answer. At worst you could find a replacement driver for ~$2 that has a PWM option; drivers based on the PT4115 are pretty common.
1502  Using Arduino / Project Guidance / Re: Peltier-based dehumidifying cabinet on: December 27, 2012, 01:56:54 am
That FAQ and all of their technical specifications provide pretty much no detail as to thermal stress considerations, and if it were a big issue to be concerned about I would expect that they would list some specification as to the number of switching cycles it can handle. It also contradicts itself with its discussion of using mechanical relays by suggesting that the relay fails before the peltier junction does? After digging around with Google I'm not denying that PWM would be preferable, but I still can't find any decent numbers as to how much of a concern this is.

Stick with the K.I.S.S. principle. A peltier junction is ~$10, and if it does wind up failing too quickly then you can revisit how you're driving it. Drive it at a low voltage and tweak the voltage a bit until you get a reasonably low switching rate. You don't really need that much cooling; At 70F (room temperature) the dewpoint is only 50F for 50% humidity and that should be a much much lower power requirement than these devices are capable of.
1503  Using Arduino / Project Guidance / Re: Peltier-based dehumidifying cabinet on: December 26, 2012, 05:33:22 pm
So what you want to do is set the cold side of the peltier to the dewpoint so that you can collect the condensation and remove it from the cabinet.

You're going to attach some sort of aluminum plate/heat sink to each side of the peltier. The hot side will need a fan to turn on whenever the peltier is active. On the cold side you will also need a temperature probe of some type (e.g. LM35 or DS18B20) to measure the temperature of that side. Use the PID library to control the power on/off to the peltier (via relay or mosfet, preferably mosfet) to keep the dewpoint temperature of the cold side stable.

There's no PWM needed here, or putting it another way there's no reason why you'd need to switch the peltier on/off more than a couple times a second to keep a reasonably stable temperature.
1504  Using Arduino / Project Guidance / Re: Starting Materials on: December 26, 2012, 02:56:54 am
I would suggest first. They're inexpensive, ship quickly, and have a lot of good starter stuff.
1505  Using Arduino / Project Guidance / Re: PWM control of many LED's from arduino on: December 26, 2012, 02:54:36 am

Bulb #2 will take PWM fine because it's obviously using resistors for current control (low power LEDs; power input 5W but light output 2.5W). Bulb #1 and #3 are using high power LEDs and will have driver chips.

It shouldn't be possible to see flickering above 100Hz and at 60Hz any flickering should be barely noticeable (do you see flickering in a 20ma/5mm LED?). I still think your problem is just that you're making the driver angry.
1506  Using Arduino / Sensors / Re: E18-8MNK IR sensor connecting to Arduino on: December 25, 2012, 01:16:45 am
It's highly unlikely that these give an analog signal. Given no documentation, I would suggest:

Red: Connect to 5V
Black: Connect to GND
Yellow: Connect to any digital pin. The pin should show a change in state (high to low or low to high) when the beam is blocked.

Another example of these sensors:
1507  Using Arduino / Project Guidance / Re: PWM control of many LED's from arduino on: December 25, 2012, 01:05:46 am
If those bulbs have drivers in them you're probably making them angry by PWMing power to them. More detail as to exactly what bulb you're using and what is inside those bulbs would be warranted.

1508  Using Arduino / Sensors / Re: IMU offset from rotation axis. on: December 20, 2012, 08:56:01 am
You will only get an approximate yaw with either an accelerometer or gyro. Any error in the calculation of how much you've turned will continually compound and eventually you'll have no idea what direction you're facing.

You need either a magnetometer (electronic compass) to tell you what direction you're facing or GPS to tell you what direction you're moving.
1509  Using Arduino / Motors, Mechanics, and Power / Re: Relay Problem on: December 16, 2012, 12:30:21 am
I don't think you'll find any ready-made PCBs/shields with 240V relays, but Mouser/Newark/Digikey would all have large numbers of options.

In order to recommend a relay, we'd need to know what DC voltages you have available (are you powering your project with 5V, 9V, 12V?) and what side of the planet you're on (set your location in your profile). Here's a good example for one that would be easily wired up though:

General relay tutorial:
1510  Using Arduino / Motors, Mechanics, and Power / Re: 2 Stepper motors with drivers - Help on: December 16, 2012, 12:15:35 am
// initialize the stepper library on pins 8 through 11:
Stepper myStepper(stepsPerRevolution, 4,5,6,7,8,9,10,11);

You've left out quite a bit of detail, but this is no good for starters. You probably want:

Stepper myStepperX = Stepper(stepsPerRevolution,4,5,6,7); 
Stepper myStepperY = Stepper(stepsPerRevolution,8,9,10,11);
1511  Using Arduino / Motors, Mechanics, and Power / Re: Cheap chinese motor controller vs sabertooth, should I just get the sabertooth? on: December 16, 2012, 12:03:00 am
The Sabertooth you have linked offers regenerative braking, thermal overload protection, and a variety of control methods. The eBay driver is just a basic H bridge. It depends on what features you need.
1512  Using Arduino / General Electronics / Re: NEED HELP HOOKING UP A NEMA 17 STEPPER MOTOR on: December 14, 2012, 12:19:22 am allows up to 1A without a heatsink. And it's on sale.
1513  Using Arduino / General Electronics / Re: measuring battery voltage on: December 14, 2012, 12:16:53 am
As lefty just said, the impedance must be 10K or less. That means the first resistor must be 10K or less.

10K/4.7K is the best choice. That should result in a voltage reading of (14.4V * 4.7K / (10K + 4.7K)) 4.6V on your analog pin for a battery charged to 14.4V and the total resistance (10K + 4.7K = 14.7K) means you're leaking very little amperage (14.4V / 14.7K).
1514  Topics / Product Design / Re: Project designing guidance - wireless event tracking system on: December 13, 2012, 12:14:47 pm
I see no requirement for frequency hopping in what you've described. You just need to set up a communication protocol between your slaves and master so that you guarantee packet delivery when collisions occur, which is to say that any time a slave sends a message it should keep retransmitting until it receives a response from the master. An XBee, for example, can do this automatically.

As to what device to recommend depends on the transmission distance and how much data is being sent. And how much money you have smiley-wink
1515  Topics / Product Design / Re: How does one begin SMD soldering? on: December 13, 2012, 12:06:33 pm
A cheap solder might be the source of your problems as well; as you can see from Lakes' example it should be pretty straightforward. What are you using?
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