Instead of trying to measure the distance between them, how about a sensor on each mount, that has a zero position.  Then the "controller" will look at each sensor independently and decide of either one is off the zero mark, and how far pos/neg from it and then they could be adjusted back to any distance.
   
  Question is...how close do you need to be aligned?  An array of sensors....maybe hall effect or proximity could be used perhaps...spread every quarter inch or however close you would need them to be aligned to.


>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 17 February 2006 15:57
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Distance Measurement
>
>
>Tim N9PUZ wrote:
>
>>I'm researching options for measuring distances in a wet, outdoor
>>environment. The task is to measure the distance between two drive 
>>units on a boat. The drives both propel and steer the boat.
>>
>>Ideally I will end up with an indicator for the crew that sits at "0"
>>when the drives are a certain distance apart and will go positive or 
>>negative from center if the drives are misaligned. The boat has 
>>provisions for trimming the positions of each drive from the cockpit.
>>
>>I'm looking for options to consider to do the actual distance sensing.
>>Water will occasionally splash around the sensor locations and since 
>>the drives will be running there will be vibration. I do not know the 
>>exact target distance right now but it is approximately 7.5 feet. The 
>>drives have places where sensors, etc. could be mounted 
>starting about 
>>a foot behind the transom and out to about 5 feet or so on to the 
>>drive assemblies.
>>
>>Tim
>> 
>>
>That should be easy with ultrasonic sound. The pulse is sent, and the 
>echo tells distance.
>The sender/receiver modules are available commercially.



		
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