@Fredo We used an analogread on the sensor board output pins. You can find an Arduino example code for the analogread function through this link.
Is it possible to buy these boards pre-made so I can throw into a project with the code?
@Michael We unfortunately don’t offer the generator and sensor boards. You can send the gerber files to any PCB manufacturer to produce it and assemble the components based on the provided BOM.
I have a ~11 years old Robomow RL-1000 still working fine. Have not found out what signal is being sent by the charging/perimeter station and don’t have access to an oscilloscope, anyone knows the signal type?
Could the sensor in this blog sense the signal from the charging/perimeter station?
If so, I would not need to build the generator, only the sensor. The total length of the wire is by the way ~150 meters.
Hi Thomas,
Unfortunately, the Robomow RL-1000 signal generator is a closed product design. We don’t know what type of signal and at which frequency is being sent from the generator into the perimeter wire. It would, most likely, be a specific signal that will only be detected by the sensors on the Robomow, therefore, it won’t work with the sensor discussed in this blog article.
Hi Brahim,
Could the circuits be tuned to provide sub-millimetre accuracy? I would like to use this for alignment of mechanical components to a stretched conductor acting as a reference.
Thanks!
@Deemoss Unfortunately, this circuit is not intended to be used for precise (sub-millimeter accuracy) positioning. The sensor-generator setup will provide a rough idea if the robot (sensors) gets too close/far from the perimeter cable.
Hi Brahim,
thanks for this brilliant post, I really appreciate it! 
One question: you stated that the perimeter wire may not be longer than 100 feet, right? Could you please short describe what would have to be done that the sender is able to power a longer wire?
Best regards,
Michael
@Michael Thank you for your nice feedback, glad that you like the post.
The perimeter wire we used to test the generator circuit was 100’ long. This doesn’t mean that the wire can’t be longer.
From the datasheet of the NE555, the maximum recommended current output of the chip is 200mA. Therefore, with a VCC of 12V, the maximum power output would be 2.4 Watt.
So theoretically, the total output resistance should be less than 60 Ohms. There is an output resistance of 47 Ohms in the generator circuit, so it leaves 13 Ohms for the loop wire resistance.
A 22 AWG wire gauge is rated for 16.14 Ohms of resistance per 1000ft, therefore, the maximum theoretical length of the perimeter wire, would be approximately 805’.
Hi Brahim
Just like Michael I really appreciate this post and i’ve a question on perimeter wire length.
If I was to increase the cross sectional area of the perimeter wire, therefore reducing the resistance of the wire, would I be able to run it over an even longer distance than 805’?
Kind Regards and thank you
Dave
@David Thank you.
Theoretically, yes but the square wave signal might be distorted at a certain length of the cable. This would be caused due to the self inductance which is caused by the magnetic field generated by the wire. In AC, the current switches its direction back and forth causing a changing field. This changing field reacts with the electrons in the wire opposing the current flow. This opposition is called inductive reactance and acts as resistance. Inductive reactance increases with the frequency of the square wave and the inductance of the wire by this formula : Xl = 2πf*L.
Where L is the self inductance of a wire and is dependent on its length and radius. It can be calculated using this tool/formula
Therefore, longer the wire, more the self inductance will be important and more this will have an effect on the generator signal.
Hi, any news on the Generator Board 3D and sensor brb in the shop ???
@tore The Generator and Sensor boards should be available next week. We’ll add the link to the product as soon as it’s live on RobotShop.
Hi, I have built the circuits on bread boards and testing with the analog read on my Arduino but am only getting a small change in values when the coil is 1mm from the loop. I get a low value of 56 and a high of about 200
I am hoping to use your design as an electronic finish line in a electronic billy cart timing system I am working on so I was hoping to get a high level with the coil 10cm from the loop. Should I be able to get a better result in a bread board?
@Aaaron Did you verify the frequency of the generator’s output square wave ? This frequency can be varied by the potentiometer and should be as close as possible to 34 Khz to match the tank circuit’s resonance frequency. You can monitor the generator’s frequency by using an oscilloscope, probing one end of the perimeter wire cable (while the other end of the cable is connected to the generator circuit output) and connecting the oscilloscope probe’s ground to the generator’s GND. You can keep the coil at a fixed distance from the loop cable while varying the generator frequency potentiometer to obtain the best results. Also, please note that the coil should be oriented correctly. As indicated in the post, the inductors longitudinal axis should be perpendicular to the perimeter wire.
Also, for better results, the generator’s power supply voltage should be between 12V-15V with at least 500mA amperage.
I think I have a bad 22nF capacitor. It only measures 16nF
I am powering the generator with a 12v lead acid battery.
The shops are all closed for a long weekend now so I will have to wait and get a replacement capacitor on Tuesday and try again.
Good news. The RobotShop Perimeter Wire Generator and Sensor Soldering Kit is now available.
Hello, I have question. Is it possible modulate signal this way? I will have more perimeter wires in earth.
Each perimeter wire will have unique signal or encode some digital ID
Robotic lawn mower will know path_ONE/wire_ID1 I am up to hill wire_ID2 i am cutting grass downhill
and Robot logic is then simple : Find perimeter wire decode path_ID and rotate right way and go to end of PATH then find next perimeter wire and decode ID rotate to right direction and again cut until is end of path …etc…
Any idea how to do that?
@Jepster This might be possible by using multiple generators with different output square wave frequencies as the frequency can be easily varied with the onboard potentiometer (about 32KHz to 44KHz). You will also have to use multiple sensor boards on the robot with different inductors/capacitors values knowing that the frequency of each tank circuit should match the frequency of its generator board.
For example :
- wire_ID1 loop cable will be connected to generator board #1 that has an output wave frequency of 34KHz. wire_ID1 will be detected by sensor board #1 that has a tank circuit with two inductors of 1mH and two capacitors of 22nF (corresponding to a resonance frequency of approximately 34KHz)
- wire_ID2 loop cable will be connected to generator board #2 that has an output wave frequency of 37.5KHz. wire_ID2 will be detected by sensor board #2 that has a tank circuit with two inductors of 1mH and two capacitors of 18nF (corresponding to a resonance frequency of approximately 37.5KHz)
And so on…
You will also have to think on how you will mount the sensor boards and the inductors on the robot as you will have a lot of inductors. Assuming you have 4 different areas, therefore you will need 4 generator boards + 4 sensor boards with 8 inductors (if each sensor board has two inductros).
Hi, really excited to see this kit can now be bought from you, that’ll make a big difference, I expect I’ll be ordering very soon! One question - how would you use this, either as it is, or modified, to allow the robot to follow the wire back to the base station for charging? I’ve seen some designs that allow the robot mower to know which direction to follow along the wire, but wasn’t sure if it was possible with this or not.