Does anyone know where you can find a cheap downward-facing optical flow sensor for measuring odometry on a general-purpose mobile robot?

I've read a few stories of people using hacked optical mice, but these don't usually work well since the lenses are designed to be used within a few millimeters of a very flat surface.

The paper Outdoor Downward-facing Optical Flow Odometry with Commodity Sensors uses this technique in an outdoor domain by using multiple optical mouse sensors fitted with custom lenses to work on varying terrain. However, I can't find anyone who's selling these sensors.

I've used OpenCV's optical flow code to effectively function as an optical mouse sensor using a commodity webcam. Has anyone tried this approach on a mobile robot, or are aware of any pitfalls? Are there alternative solutions?

Servo test code that might do what you want to do.

Thanks. That's actually very helpful.

Is there anyway to convert a String instance (not a character array!)

Why are you NOT using a char array? Do you really need the crutch?

Why are you? I like making my life simpler, not more difficult. Do you really want to worry about buffer overflows? People really need to ditch C and join the 21st century. Object orientation is here to stay.

It does, which returns a long.

Does it? It's not listed at http://arduino.cc/en/Reference/StringObject

What would be a better source of documentation?

Is there anyway to convert a String instance (not a character array!) directly to an unsigned integer? All the examples I've found use functions like atoi() which require a character array...which seems to defeat the point of using the String class if I still have to convert it back to a character array every time I need to parse it.

You're missing the fact that the pin number on the AVR is not the Arduino pin number.

In fact, if you look carefully at the schematic you posted, AVR pin 26 (PB7) is connected to both Arduino pin 13 and IC7A, the buffer for the LED.

Thanks. Yeah, I missed that. I didn't realize the pin number used in the code was different from the actual chip pins.

I'm playing around with an Arduino Mega 2560 (SainSmart manufacture), and I'm confused by a disparity between the schematic and the standard example "Blink" program.

The schematic indicates the built-in LED is on PB7/pin 26. However, the Blink example uses pin 13.

I've confirmed the LED is indeed on pin 13, but changing the pin number and re-uploading the Blink program, confirming it doesn't blink, reverting it to pin 13, re-uploading, and confirming it blinks. This is frustrating, because now I can't trust the schematic for predicting which pins I should use.

Why does the actual device have a different pinout than the official schematic? Is SainSmart mis-wiring their version of the board or am I missing something?

I'm trying to design a standalone Arduino Mega + Lipo device, but I'm finding this difficult as nearly all Lipo batteries (and Lipo riders) only handle 3.7V input and provide 5V regulated output, while the Arduino's onboard regulator requires 7V input to give the AVR it's regulated 5V.

If I wanted to use a Lipo rider that provided a 5V regulated ouput (e.g. this), how difficult would it be to bypass the 5V regulator on the Arduino Mega?

I'd like to simply wire two lipo riders in series for an ideal 7V supply, but all the advice I've heard recommends against that due to concerns with charging difficulty.

If you really want it quick, wouldn't it be both simpler and preferable to accept a data stream over USB rather than poll a buffer?  That way you minimise the operations and ensure the information is coming as fast as the Arduiono can send it.

You can use "if no change do next" conditions to determine what is sent.

Yes, of course. I wasn't sure if this was possible. Thanks.

What's the best way to program an arduino so its sensors can be quickly polled over USB?

I have a small project with a few dozen on/off contact sensors and a half-dozen analog sensors that I want to be able to quickly relay value changes to a "host" computer. It's a mobile platform, so I'd like the system to be as close to real-time as possible.

My thinking is to use a pull-method by adding any sensor that's changed since the last polling to a special buffer, and when the host polls the arduino, send it the most recent values in the buffer and then clear it.

Is there a more efficient push-method, where the arduino can notify the host of sensor changes?

Yes, you'll probably want to look at a high-current mosfet transisitor, like those used to drive motors. You could wire the extra supply to a mosfet's source, and then wire an arduino pin to the mosfet's gate to turn it "on" and "off".

You could try wiring that together yourself, but if you're unfamiliar with soldering custom electronics, I would suggest you look at one of the high-power motor control arduino shields.

No, I want to use my arduino to power a 12V converter which convertes to 220V if possible WITHOUT anything like a battery and just need to turn on/off it.

By "use my arduino to power" do you mean using your arduino's regulated power supply, or using the output of one of the arduino's pins to feed into the 12V converter? Is your arduino connected to a battery or a wall source?

If you're just looking for a way to power a 12V device using a 5V battery, I think you're looking for a 5V to 12V step up converter.

Can you wire the "load" outputs on two single-cell lipo chargers (e.g. this or this or this) in series, to get a larger voltage that's still safe and easy to recharge?

I understand the dangers of wiring and charging the lipo batteries themselves in series. If the cells become unbalanced, then one of the cells could potentially explode or burst into flame. This is probably why so few online stores sell multi-cell chargers for embedded applications...

However, is there still a danger will when it's chargers, and not the batteries, that are wired in series? Shouldn't the voltage regulators on these chargers, and the separate charging circuitry, effectively balance the cells when charging and discharging?

This question is related to an earlier question.

Thanks CrossRoads and DuaneB.