slightly OT, need some electronic circuit help

[Shane Hathaway]

On 10/08/2012 11:57 AM, Michael Torrie wrote:
> On 10/08/2012 11:36 AM, Hugh Clark wrote:
>> Perhaps I don't fully understand the problem, but couldn't you use an
>> H-bridge to control the motor (only needing 1 DC power supply) and an ADC
>> on the Arduino to measure the position?  The code in the Arduino would
>> provide the basic feedback loop allowing you to set rough ADC values from
>> the pot for your 3 positions.
>
> Of course. I said all that before[1].  Digital circuits are nice, but
> nothing beats the reliability of a simple analog circuit.  I found some
> good info on op-amps, how they work, unipolar circuits, and exactly what
> the different resistance values give you.  My application is in a very
> rough environment (dirt, dust, vibration, and extreme temperatures).
> The simpler the circuit the better.  Arduino is way overkill for this
> application.

The large current requirement (10A) and the need for a middle position 
make the circuit interesting and difficult to achieve using low cost 
analog components.  An analog H bridge would work well if you only 
needed 2 positions.  You can't dump that much current through an 
ordinary op amp.  (Audio amplifiers use big, expensive op amps that 
easily surpass the cost of an Arduino.)  PWM is the usual solution for 
handling that much current.

However, can you achieve the middle position using a simple mechanical 
spring?  That would allow you to use a very simple H bridge.

It would help a lot to understand the application better.  What kind of 
resting position do you want?  When the power is lost, do you want it to 
revert somewhere, or hold its position firmly/loosely?

Shane