Hi guys! I just signed up here, im a total noob but with big plans.
So my idea is to make a automated cutting height for my combine harvester, its a Claas Mega combine from 1996, it has its own Autocontour system, but it doesnt work, costs a big chunk to get it back and running, i tought about making my own.
So basically, the hydraulics are controlled by solenoid valves 12V, i tought about making a steel plate on springs witch will slide and copy the terrain(because without the steel plate grass and straw will interfere with the sensor), than the ultrasonic sensor will read the distance from the steel plate.
Optimal cutting height would be about 15cm, so if the distance between the steel plate sliding on the ground is bigger than 18, the arduino pushes 12v to solenoid for cylinders to go down to distance 15cm, but if the distance is 12cm or less, it gives 12v to solenoid for cylinders to go up back to 15cm. I hope you will understand my idea.
I need to know, what board to use, how to make that board to give 12v signal to solenoids and e.t.c also i need a man to write me a code (i will pay ofcourse) I NEED A GUY WHO WILL HELP ME TO GET TROUGH THIS 
Have you factored in the ultrasonic noise generated by the environment you are operating in? What will the ultrasonic bounce off of in your design? Soil? the grass or grain stems? Don't you think this should be tested before you continue the design?
It will bounce off from the steel plate
Combine while working generates a lot of noise, but not high pitched ones, like whistle and etc, just a lot of decibels.
WE are discussing ultrasonic sound! Any sliding action means friction, means lots of ultrasonic generation. Testing before implementing is necessary.
What about using a potentiometer to read the angle on the plates. Get something like a ride height sensor for a vehicles, they are often used in diy agricultural machine control. The automatic header height controller on my combine uses the lift cylinder pressure to detect the down pressure on the headers tires to adjust height.
This isn’t really that straight forward as you need to compensate for abnormal terrain. Say for example the plate drops into a rut, then you will crash your very expensive header into the ground.
You might find a bit more useful information over on the AgOpenGPS Forum
You need to close the loop and sense where your actuator is as well. Just a simple TOO HI/TOO LO will chatter and oscillate. Linear magnetic sensor on a shock absorber connected to the ski will give better, more reliable signal than sonar. It also replaces the springs, simplifying the mechanism. Magnetic sensor will not clog with dust or give "jumpy" readings as the sonar ones do.
Sonar is sensitive to material and angle.
Is ultrasonic so wise around big noisy machinery (noise, including inaudible sounds caused by the moving parts could easily saturate any ultrasonic signalling). Some sort of optical ranging (assuming it can be shielded from dust/dirt/grain) or magnetic sensing might work better. Or have a height measurement wheel on the end of a lever and measure the angle of the lever at a fixed pivot.
I would consider a RADAR module. Here is alink to get you started. RADAR is used in the automotive arena so there are some rugged devices available and surprise they work on 12V.
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