Designing a 12 volt circuit to control a sub-fractional gear motor that will sense the presence of the motorized devise, close a relay that will activate the gearmotor to open a gate and then reverse the gearmotor to close the gate after the motorized vehicle has cleared the gate. The mechanical items are easily done but at 83 I have forgotten the little I picked up, low those many years ago, on types of prox. sensors and if there are any that would not be triggered by a pet. The sensor is going to have to be IP65 for outdoor use. The motor drive amperage is less than 2 amps. Plan is to use a 12 volt DC yard light power supply. Suggestions please.

 

What is this motorized device?
Underground "Loop Detector" comes to mind.
Depending on the size of said motorized device and the physical layout of the gate a Hall Effect sensor and a magnet installed on the device may be all that is needed.
More info please.

 

What is this motorized device?
Underground "Loop Detector" comes to mind.
Depending on the size of said motorized device and the physical layout of the gate a Hall Effect sensor and a magnet installed on the device may be all that is needed.
More info please.

The devise is a robotic lawn mower. In order to mow both the front and back yard it has to pass ( only once into the front yard and then back to the charging station. Planning a hanging gate that will raise and lower to allow the devise to pass between the fron and back yards. Thanks for your interest.

Jim

 

Does the mower use a buried wire for navigation?

 

Does the mower use a buried wire for navigation?

It is a new Kress that is GPS controlled

 

How fast will it move when approaching the gate?
Can it be programmed to stop at the gate and wait until it's opened or does the gate sensor need to be triggered before arriving at the gate?

 

How fast will it move when approaching the gate?
Can it be programmed to stop at the gate and wait until it's opened or does the gate sensor need to be triggered before arriving at the gate?

It has to remain moving. We will have to have the gate fully open when it arrives.

 

I'm thinking of trying a hall effect sensor?
How far from the gate do you estimate the sensor would need to be placed regarding speed of the mower and time to raise the gate?

 

I'm thinking of trying a hall effect sensor?
How far from the gate do you estimate the sensor would need to be placed regarding speed of the mower and time to raise the gate?

I can control the speed of the gate going up within reason. Let me get a little more information from the company tomorrow and I will get back to you. Thanks for your assistance.

Jim

 

I’ve used a laser pointer inside a 15mm pipe aimed at a a pipe opposite with an opto transistor several cm away from the mouth. Works fine in a shaded area. A processor to monitor for sudden changes to filter out changes in daylight. ATtiny85 should suffice

 

A Field disturbance sensor can respond to the presence of a device with an electric motor and some conductive framework. That will require, in this case, probably an aluminum foil mat for the mower to pass over, with the foil NOT GROUNDED, but connected to a sensitive amplifier similar to a voice operated switch.
The concept of operation being that the electric motor will radiate some electrical noise signal that can be amplified and used to trigger the relay.

 

A second option is photo-electric beam break sensor arranges so that the mower breaks the beam as it approached the gate from either side. That will allow one sensor instead of two and avoid needing additional logic. AND security alarm companies can provide sensors with a range of at least 50 feet, although I am thinking that 20feet would be quite enough.

 

It has to remain moving. We will have to have the gate fully open when it arrives.

Is there any form of communication with the mower while this is happening? I'm thinking that if the mower announces that it's heading home for a charge, the gate could open and then close when the mower reports itself docked.

It's going to be challenging to differentiate the mower from, say, a kid on a scooter. How serious a problem is it if the gate opens for the latter?

I wonder if the mower makes a unique sound that could be detected. Humans have a great vision system and if a human were sitting there controlling the gate, it would be simple. If the human is blind, the next easiest sense to use would be hearing.

It seems like the software is able to tell the owner exactly where the mower is. That means the mower transmits its location. Maybe you could just look for a signal at the appropriate frequency?

 

I already suggested a scheme that is workable.
The fact is that there is not nearly enough information provided, and apparently no interest in any other schemes.

 

I already suggested a scheme that is workable.
The fact is that there is not nearly enough information provided, and apparently no interest in any other schemes.

You think an un-grounded piece of foil laying on the ground is workable? I thought that was a thought experiment, not a practical solution.

 

Actually, the photo-electric beam-break scheme could be workable. AND, also, a sound sensing system would also be workable and probably much simpler because sensor positioning would not be so very critical.

 

a sound sensing system would also be workable

Only if you can readily differentiate the sound level during its normal operation to when it's approaching the gate.

 

Only if you can readily differentiate the sound level during its normal operation to when it's approaching the gate.

Certainly that is true. But my observation is that robotic electric mowers have a fairly unique sound frequency spectrum that should not be very difficult to differentiate from the rest of ambient noise.
Electric rotary mowers do have a particular sound characteristic, at least my electric rotary mowers do.

 

Electric rotary mowers do have a particular sound characteristic, at least my electric rotary mowers do.

For mine it's just the sound the rotating blade makes.

So how will you know when that sound is approaching the gate vs. when it's mowing?

 

The way to localize the source of a NEARBY sound is by amplitude and frequency. That implies an amplifier with an adjustable frequency response and "fairly low" distortion, driving an adjustable setpoint switch, and also a microphone that is weatherproof and fairly directional. None of those requirements are difficult, probably the hard part will be the weatherproof microphone. The adjustable frequency response will probably be as simple as an L-C tuned circuit set for the mower noise pitch. Rotary mowers do have a characteristic pitched noise. Sound operated switches have been around since 4-pin vacuum valves, so no problem there . Likewise, audio amplifiers with less than 1% distortion. It might even work to use aa PLL IC to detect the frequency. Probably there is a system already in the archives of this website forum.
AND it will work because as the mower approaches the gate the sound will be much louder, if the microphone is placed correctly, and is not excessively sensitive. THAT will be the most challenging part of the project. Plus the gate opening and closing.
For the actual circuit drawings, commercial rates would apply.