If you just want three images side by side they can be positioned just as you would position three letters or boxes, no need for minipage wrappers etc. I also added p to your optional argument as not having it makes it more likely the float will go to the end of the document.

\begin{figure}[htp]

\centering
\includegraphics[width=.3\textwidth]{i/houghtrain.png}\hfill
\includegraphics[width=.3\textwidth]{i/houghframe.png}\hfill
\includegraphics[width=.3\textwidth]{i/houghspace.png}

\caption{default}
\label{fig:figure3}

\end{figure}


3 images side by side
An LED embedded in a small translucent item (say half the size of a pack of cards) that would flash on briefly if the object was disturbed or tipped over.
I immediately responded that a piezoelectric sensor/generator inside the object wired to an LED would do it.
However, when I tried to demonstrate this concept using a piezo buzzer I liberated from an old phone, I could only get the LED to register a dim blip when I smashed the piezo buzzer with a blunt object.
How would I ensure that a piezo sensor/generator would actually light up the LED adequately without the application of blunt force trauma.
As I mentioned, space would be an issue so no large parts, breadboards, or really complex circuitry.
I'm just trying to figure out the easiest and smallest way to accomplish this simple task.
Thanks a lot for any help you can give me!
