I know this would be possible but no idea how to go about it.

I am wanting to install a distance laser on my farming planter with a remote readout in tractor cab.

I want to be able to measure the vertical distance between planter frame and ground level and calibrate readout to zero when planter feet are at ground line; and then when I lower planter into ground (the distance between ground level and planter frame will decrease) I want the readout to show difference in centimetre possibly to one decimal.

 

I’m thinking that ultrasonic sensors would be the best option, similar to the way vehicles have reverse warnings. Modules are available at low cost designed to work with Arduino and Raspberry Pi processors. I’ve seen them quoted as being able to measure distances between 2 cm and 400 cm

Given the unevenness of the ground I doubt that 1 mm resolution really has much meaning but 1 cm should be possible

 

Welcome to AAC.

I am assuming the variation in distance of any given cm² of area beneath the planter is greater than 1mm, and even possibly 1cm—or more. This means trying to bounce anything—light or sound—from the surface will result in confusing values and with 1mm resolution, extreme false precision.

I think I would approach this in two steps:

1. Probe the surface to determine the appropriate value for a meaningful average height above the surface.

In a pure surmise, I imagine this step involving lowering some sort of flat probe of an appropriate surface area, instrumented with a pressure sensor.​

​

The probe would be lowered until the pressure caused by its contact with the ground indicates a first contact, then lowered until it reaches a pressure indicating the probe has compressed the soil to the point of uniform distance from the planter frame.​

​

Useful calibration might require several test spots—for this to be useful you have to have some idea of the characteristics of the (I assume tilled) field and the soil. What we are trying to do is eliminate the “false” variations cause by surface disturbance that can’t be used to understand the actual effective depth of the planter when in operation.​

2. Use this average height instead of measuring for each implantation.

This should provide a consistent planting depth with an accuracy dependent on the consistency of the field surface and soil compaction. This is almost certainly much more than 1mm and may be a large percentage of the intended planting depth rendering it an imaginary exercise in “precision planting”.​

Alternatively, this could be replaced with some sort of conductivity test that would calibrate a sensor on the part of the planter that actually penetrates the soil. Instead of concerning yourself with the distance from the soil, you would be measuring the actual depth into sufficiently compact soil you have penetrated.

This method depends on the consistency of the soil’s characteristics (in this case both density and water content). Part of what I am (possibly erroneously) assuming is that it is more important for the planting to be in soil of a certain density than a certain distance from the planter—and that in truth, the distance from the bottom of the planter frame is already just a proxy for this.

This method, might be more successful using pressure than conductivity since (more surmise) the pressure from penetrating soil of density n is going to be the same even if it appears to be varying from the visual soil tops.

 

Welcome to AAC.

I am assuming the variation in distance of any given cm² of area beneath the planter is greater than 1mm, and even possibly 1cm—or more. This means trying to bounce anything—light or sound—from the surface will result in confusing values and with 1mm resolution, extreme false precision.

I think I would approach this in two steps:

1. Probe the surface to determine the appropriate value for a meaningful average height above the surface.

In a pure surmise, I imagine this step involving lowering some sort of flat probe of an appropriate surface area, instrumented with a pressure sensor.​

​

The probe would be lowered until the pressure caused by its contact with the ground indicates a first contact, then lowered until it reaches a pressure indicating the probe has compressed the soil to the point of uniform distance from the planter frame.​

​

Useful calibration might require several test spots—for this to be useful you have to have some idea of the characteristics of the (I assume tilled) field and the soil. What we are trying to do is eliminate the “false” variations cause by surface disturbance that can’t be used to understand the actual effective depth of the planter when in operation.​

2. Use this average height instead of measuring for each implantation.

This should provide a consistent planting depth with an accuracy dependent on the consistency of the field surface and soil compaction. This is almost certainly much more than 1mm and may be a large percentage of the intended planting depth rendering it an imaginary exercise in “precision planting”.​

Alternatively, this could be replaced with some sort of conductivity test that would calibrate a sensor on the part of the planter that actually penetrates the soil. Instead of concerning yourself with the distance from the soil, you would be measuring the actual depth into sufficiently compact soil you have penetrated.

This method depends on the consistency of the soil’s characteristics (in this case both density and water content). Part of what I am (possibly erroneously) assuming is that it is more important for the planting to be in soil of a certain density than a certain distance from the planter—and that in truth, the distance from the bottom of the planter frame is already just a proxy for this.

This method, might be more successful using pressure than conductivity since (more surmise) the pressure from penetrating soil of density n is going to be the same even if it appears to be varying from the visual soil tops.

Thankyou for your reply.. yes you are correct the reason for this exercise is to try and plant the seeds at the appropriate depth to plant into moisture but not too deep; we have variable soil types which compact differently as you've mentioned and setting up the planter using height blocks on the lift rams gives up to a 100mm variance when planting in the softer to tighter soils. I will consider your probe idea but unsure how that would work when traveling at 6.5-8km/h, I have also considered just going old school and using a floating land wheel with a height stick but since there is so much technology available now thought is worth a shot. I have looked into the ultrasonic sensor which looks like it may be better suited for this application than laser as it is a very dusty environment and non reflective surface the laser would struggle. As you mentioned I am aiming just to get an average reading at a single point on plough frame, it doesn't have to be highly precise it is more to get a bit of an idea when adjusting height when traveling over different soil types (up to 6 soil changes per run) rather than just guessing how deep it is or getting out and digging in the soil to keep checking i am hitting the moisture.

 

different type of distance measurement are available.

for contact measurement encoder or potentiometer etc can be used. this allows for high resolution. different mounting methods can make this easy to install (like string encoder).

for contactless options one could use ultrasound. it is low cost but target area need to be large. also for best results one should average results and compensate for temeperature. resolution is normally in the cm range but it could be better too.

the other option is laser distance. the advantage is small target area. this makes it suitable to look at moving part of mechanism. tut this can be a problem too if there is a single speck or reed blocking the view. low end lasers normally get you resolution in the cm range. better ones can do fraction of a mm but will cost a pretty penny.

so if the idea is to use laser, you probably want to keep it safe and clean, preferably way up above ground level so that kicked up dust and dirt do not cause a problem.

if you are looking for a laser and want off the shelf product that is rugged, has very large lens (inch diameter), distance resolution of 2-3mm, long range (10m), and uses visible light (so you can see the spot it looks at), i would consider an industrial product like O1D100 from IfmEfector. should be some $200 a piece.