I have had experience with LiPos and salt water and it was not great.  If the terminals on the LiPos get submerged in the salt water you can get extremely rapid discharge and the accompanying fire/explosion. 

As a fellow reloader who has looked into digital scales and wonder why they are so much?  I have thought about buying load cells and trying to implement a digital scale using Arduino or some other MCU to read the cell and display the results.  Load cells are available through Mouser, DigiKey and others, but buying them one at a time will kill your budget.  Once you have the load cells you are going to need to get an instrumentation amplifier chip or make one up using two high quality Op Amps.  Depending upon the dynamic range required you will be probably need better resolution on the analog to digital convertor than the one on Arduino so you will have to do the analysis to see if you need a 12-,14-,16- bit ADC or higher resolution.  One channel of the ACD can probably be used to read a high-accuracy temperature sensor so you can make adjustments to calibration based upon temperature.

Once you have the pieces together that you paid through the nose through as you bought them in low quantities you then have to do the PCB design to get a low drift scale.  Some designers of digital scales say low drift and load cell cannot be used in the same sentence.

This is how I solved the problem I bought a tuned balance beam scale from a guy called Scot Parker, search 6mmBR.com for his contact info if you desire.  I can see needle movement on the scale from one granulae of powder and more importantly it is repeatable.  I have my scales on a piece of 4 inch thick 2 foot x 3 foot piece of granite to help isolate it from ambient vibrations.  I have reloaded for over 35 years and have taken a lot of time over the years thinking about these things.

Maybe this helps, maybe it doesn't but this is how I do it and a little background on load cells.

wade

John I'd like you to meet Google and Google I would like you to meet Google.

I googled "laser range finder using camera" and found this as the first hit https://sites.google.com/site/todddanko/home/webcam_laser_ranger

I guess my response started out a little smart -aXX'ed but as I have told a lot of younger engineers "If it were not for google I would have to know something"  Google and an inquisitive mind may be the most powerful tool available.  Google even spells things correctly for me.

wade

There are equations that give you very accurate values for the azimuthal and elevation angles for the location of the sun based on your location and time, if you have these you can just point the solar panel in that direction.  An analysis would need to be made to see if the time from an RTC would be accurate enough.  A GPS could be used if the RTC drifts too much, doubtful but a possibility, and the GPS would also alleviate the need for you to enter your latitude and longitude.

Just my two cents and I overcharged,

wade

I think the hardest part of building a laser range finder (LRF) is the sensor that picks up the reflected beam off of the target, with modern MCUs the timing is not much of a problem.  The signal reflected back by the target is very small and that is what makes the laser difficult to detect.  Most commercial LRFs use an avalanche http://en.wikipedia.org/wiki/Avalanche_photodiode photodiode (APD) as the detector.  Here http://www.edmundoptics.com/electro-optics/detector-components/avalanche-photodiodes/2646 is a price list of APDs from one of the larger optics vendors and you can see that they are not cheap, manufactures get a huge break when bought in production volumes.

Another option hobbyists have used is to use a visible laser and view the reflection by a video camera and process the imagery and do the geometry to determine the range. I am not at all well versed in this method but I believe it has been posted on this forum.

Not trying to discourage anyone, maybe there are other methods,

wade

I forgot to add that this needs to be a portable system that is easy and quick to set up, if this was to be a fixed permanent system the laser would be a great idea.  After doing some work in optical comms I am surprised I did not think of it in an early go around.

Thanks

wade

I am looking at building a system to measure time of arrival of a bullet at a target and would like timing resolution of .1 millisecond where there is a distance between the base station (Arduino UNO) and the microphone picking up the bullet's passage.  There is no network or wiring of any kind between the base station and the downrange microphone so either I need an RF system that can transmit a pulse to the RF receiver at the base station when the bullet arrives, or a means such as a GPS unit at each end to synch the clocks up for reducing the effects of drift. The GPS solution would also require an RF solution, to transmit the number of cycles since the last PPS.  I have implemented an XBee system on another project and I would probably use this for the GPS solution if I had to go that route.  The distances are up to a mile.

I would prefer the first type of solution as I would not have to have a GPS unit at each end just outputting its PPS to synch the clocks.  Does anyone know of a low-cost RF-based method of transmitting and receiving the pulse, think of it as a switch opening or closing.

The mic unit has an amp and signal conditioning that outputs a TTL pulse a noise load enough to be a bullet is heard.

Thanks

wade

With a better picture and/or schematic and source code it is difficult to help.

wade

Conformal coating with the lead wires attached will probably get you 98% of the way towards waterproofing.  I agree with the last poster that use wired comms instead of the XBee, I like XBee's but in any situation where wires are easy I will use wired comms a lot less complexity and headaches.

You probably want to look in PID algorithms for controlling the rudder correction, I doubt you need a full-up Kalman filtering approaching with only one sensor and what I imagine is a pretty flat solution space.

Free advice and overpriced at that,

wade

I recommend either Iteadstudio.com or Seeedstudio.com, I have had jobs done nicely at both places.

wade

Control of the focus mechanism is probably not a problem if the message protocol is available from Tamron.  Are you looking at automated focus control where the Arduino MCU does the image processing necessary to focus the camera, if this is the path you want to go you will probably find Arduino does not have narly enough processing power.  Controlling the focus as you look at an image generated from the camera say with a potentiometer is doable as your eyes do the image processing.

wade

Most of the affordable IR sources both lasers and LEDs are in the near infrared and regular glass/plastic works fine as a lens.  I guess the targte could be made up of an array of photodiode or phototransitor of the size you want and make sure the spot size of the laser is large enough to bridge the gaps in the target array.

Alternatively, defocus the laser until you get a spot size equal to one-half the target size and use one photo-diode or -transistor.  I like this method better.

Be careful on the power of the laser as IR can easily cause permanent eye damage.  Saftey is another reason the second method may be better because a large spot size will have a lower power density than the same laser focused tightly and thus less apt to cause eye damage.

Tritemeo,

What is the IC called out it seems you have labeled as an LM2961 but I have a hard time finding a datasheet or even a chip with that designation, can you help me out?

Thanks

wade

You mentioned you were supplying 5 V to the XBee, you should probably put a regulator to take that down to 3.3 V as that is what XBees like.

Given the app I assume the object you would like to know whether you are in proximity or not is the ground and you can use radars for this but a quite an expense in money, weight, size and power all being critically scarce resources on UAVs, if you really need this look at laser range finders.  Another ground avoidance technique is to load DTED aps on board and use a baro altimeter for ground avoidance. 

If you are trying to measure proximity to objects in the same plane (geometric) as you a different system is needed as you approach speed, reaction time and awareness distance are all related.  This is true also for ground avoidance but your approach speed in most cases is far less.

I worked on a UAV that is deployed and a lot of people have tried to work the same problem as you.