Hi Guys,
I looking for a sensor to put onto a motorized trolley in a greenhouse. I need to be able to sense the end of the row and stop the trolley. I currently an Arduino as the controller and everything is working well with respect to this side of the project. Currently there is a micro switch on the trolley to stop it, but this is very mechanically and prone to problem due to the rails that the trolley uses.
The greenhouse floor is white and I was wondering if there is a sensor with will sense a black line paint on the floor in each of the row. I see that the IR robot sensor would be suitable except the distance between the trolley and the ground is about 200-300 mm and the robot IR sensor do not work for this distance.
There are about 100 rows in the green house and any solution would need to cost effective and easy to implement in each of the rows.
Excellent question. Generally, I’d say that the IR sensor with a mount to position it more closely to the strip would be the way to go. Although, another option may be to place an item on top of the greenhouse floor, that when used with an ultrasonic sensor (I’d recommend using a running average within an array to filter the output) could be used to detect the end using a simple function written on your arduino. I’ve linked a suitable sensor below that you should be able to use in this project.
Great question. The sensor that I’ve linked is a stock standard, personally for a weatherproof sensor with a better quality I’d recommend an item such as that which I’ve linked below for your project. It’s weatherproof/waterproof and has a 0.25 m to 4.5 m range in air.
Have a great day!
P.S. This is a great tutorial for how to get setup using sensors such as this.
What about a reflective sensor. I could put some reflective tape on the floor of the green house. With the distance measuring method we are a little concerned about trip hazards
That sounds like a great idea, the only issue that I can see is that the ambient light in the room may make it more difficult to calibrate the sensors properly, but that should still be a viable option. I’d also recommend still having the micro switch included as a backup in case there’s any failures. All the best with your project! Make sure to let us know if you’d like to add this to the projects section too for a potential store credit too, I’ve attached the link below.
Excellent question, that’s going to be highly dependant on the lighting in the area. If you can set up a light to shine upward toward the trolley (or have one mounted to the trolley with a reflective surface underneath) and use a light sensor you should be able to use the following sensor to be able to detect the end of the row.
What about a hall effect sensor and a magnet on the floor. The sensor could easily be mounted inside a sealed plastic box for IP rating (waterproofing). Depending on the magnet, hall effects can have quite a long range.
Hi Adam
There are a vast array of sensors out there. Mechanical, optical (through beam and reflective), magnetic, proximity and so on. Each type having its own pros and cons. Also some can be quite expensive. You don’t say how you are stopping the trolley. Are you signally your controlling device (Arduino ?) or is this a limit switch.
If you don’t have limit switches you should seriously consider doing so. If your trolley is any size you could cause some serious damage if it happens to get away or out of control. Limit switches are not just micro switches but units built to do this job. Usually are sealed and come with several actuating methods. They should also be divorced from (ie not connected to) controlling electronics but physically cut supply to the motor. They are usually change over (NO, COM, NC) and to counteract motor overrun arranged a diode to be switched across the motor to bring this to an instant stop. Also a diode across COM to NC to allow reverse voltage to be applied to the motor to reverse it off the limit situation when this contact is open circuit.
You also don’t indicate how the trolley is driven. Motor and supply (battery??) on the trolley, cable, motor on trolley with supply separate and some pick up arrangement. If motor and supply are co-sited on the trolley limit switch wiring would be fairly straightforward. If not there would be a fair bit of wiring involved but I don’t think there is any way around it.
The reason for keeping limit switches as a hard mechanical switch off is that if control electronics malfunction or power switching semiconductors fail this often is in the short circuit situation and any motor is likely to run full speed irrespective what the controlling arrangement is telling it to do. Usually some form of disaster.
Let us all know how you get on
Cheers Bob
