I am looking at building an ROV and was wondering whether I could use a Piezoelectric material to generate some energy. I was wondering how I would calculate the watts output by a piezoelectric material as a function of the pressure (so I can see how much energy it generates according to how deep the ROV is).

Fair enough I suppose, however here's another one: HUGE_VAL isn't defined http://www.cplusplus.com/reference/clibrary/cmath/HUGE_VAL/

I was trying to include a well known C library (LUA) in an Arduino project. I am having a lot of errors coming up from what I thought were standard defines, for example right now arduino is not recognising _IONBF, _IOFBF, _IOLBF, these are usually included in stdio.h (which I have included).

Is there something I'm missing here?

I am looking into making scripts for my Arduino that it could download and then run without restarting the Arduino. I have in the past used the LUA library for this task, however I am wandering whether even the Arduino Mega 2560 will be able to run it? Does anyone here have experience with scripting like this on the Arduino or a suggestion for a different approach?

Do you know the names of any?

I'm not entirely sure what you mean by that? However I am not referring to only software lockups, but also failures in the hardware itself (for example if I just came along and smashed the Arduino with a hammer I would want this other circuit to come into effect).

I would like a circuit to come into effect if my Arduino locks up. Is it possible to get a relay that relies on a constant output from the Arduino?

Fortunately does not require getting any data from the mega, just the alive check. I've been experimenting with some shields recently, and I've noticed that if I don't connect them correctly they 'hang', so while the microcontroller might still be ok it would need a reset to continue processing. I know ideally the bugs should be fixed in the code, and I will do this as best as I can, but it would be great if I could get the Uno to try resetting the Mega if it doesn't get an alive signal, and then waiting a fixed period before activating failsafe measures.

Is there anyway to reset the Mega from the Uno without getting a servo to actually press that little reset button?

I am looking for an efficient way to communicate between 2 arduino's (without using intermediaries such as XBee or IP).

I have 2 Arduino's at the moment (an Uno and a Mega), now I want the Uno to regularly check (1Hz) whether the Mega is still alive (ie, hasn't fried itself somehow), and if it is not alive execute some failsafe procedures.

I am building an airship similar to Blimpduino. I am aware most servo's only rotate 180 degrees however I was going to get around this by using a 2:1 pinion gear ratio (same way Blimpduino gets around it).

What I don't have is an axle that has a pinion gear on it that I can turn, in Blimpduino they use a Lego axle but I can't do that in mine because I have heavier motors and a greater length axle.

I am looking for the ability to control an axle with 2 electric motors either side of it. I have a servo to rotate it, however I am not sure how to mechanically link the 2, I would imagine the servo would have a pinion gear put on it that would drive a pinion gear on the axle, but does anyone know where to get axles with pinion gears already mounted on them?

OK so I still can't get this going,

Servo has signal connected to digital 9, positive connected to lab power supply, negative connected to lab power supply, and there is also a wire connecting the negative lab power supply terminal with the gnd in the arduino.

Yet no movement, I am following the Sweep tutorial (and the model is posted in the original post)

use pwm to keep the temperature a hair above the freezing point.

Problem is what if the ambient temperature is below freezing point? Wouldn't I need a colder surface than ambient to collect condensation in all cases? Also I would rather stay away from playing with temperature sensors and voltage regulators, seems like swatting a fly with a shotgun.

also, i think an ssr would not be the right tool for the job. a good logic level mosfet might be more appropriate for switching.

Why do you say that?

I am trying to build a dehumidifier for collecting water from air. The goal of this project is to produce at least 50ml of water in 8 hours under extreme and varying conditions, using < 10A of current and 12 V of DC power that is extremely durable.

The extreme conditions I speak of would be -60 degrees and 10% humidity, however I will really take what I can get (as I realise this may be quite a stretch).

So far I have got the following materials:
158W Peltier Element
Noctua NH4-D14
Arctic Silver Thermal Compound
Generic Lab Power Supply

I am looking for:
Solid State Relay for DC rated for 20A and 15V.

Putting this altogether and running it at 12V makes the surface of the Peltier go to -6 degrees. It quickly collects condensation however before it can run off into the collection vessel it freezes, even if it is hung upside down or sideways. So at the moment I am really looking for a way to prevent my water from freezing before it runs off.

Woud like to hear your thoughts.

So after some further research, it seems what I am looking for is a solid state relay. However all the ones I found are rated for AC, when I need to relay a DC circuit. Any ideas where to get one that works for a DC circuit?