Hi All,

Sorry if this is the wrong place to post this question.

I'm working on a design for a system that needs to transmit a basic binary ON/OFF signal to a receiver ~200 m away in an outdoor environment. I'm looking for any assistance with the selection of the RF transmitter/receiver. At the moment everything is in conceptual phase and I haven't decided on a processing platform either, although there is very little processing required (basic combinational logic and timing).

Ideally, I would like to find an all-in-one device that can perform both the processing and handle the transmission/reception but if they are separate components that is also fine. Does anyone have any suggestions on devices or tips on how to approach the above requirements?

Many thanks,
Shaun

 

you could check out the lora feathers from adafruit. Long range 433mhz band packet radios with a bunch of forum support.
https://www.adafruit.com/product/3179 I think sparkfun has a line as well. Thats where I would start.

 

Welcome to AAC.

Is this a homework assignment?

 

you could check out the lora feathers from adafruit. Long range 433mhz band packet radios with a bunch of forum support.
https://www.adafruit.com/product/3179 I think sparkfun has a line as well. Thats where I would start.

Hi @jiggermole,

Thank you for your input. The Adafruit module does look promising.

 

Welcome to AAC.

Is this a homework assignment?

Hi @Ya’akov,

No, this is not a homework assignment. I just don't have the relevant RF exposure and would like to narrow down my options for component selection/costing.

 

Hi @Ya’akov,

No, this is not a homework assignment. I just don't have the relevant RF exposure and would like to narrow down my options for component selection/costing.

OK, since you show yourself as "student" this was important to ask due to AAC rules.

As far as your problem goes...

It would be exceedingly helpful to get an idea of the application. After all, this is part of your notional solution, not the problem. You may be prematurely considering it, and since you don't have experience you can help those of us who do by laying out the application so we have some context.

There are many directions you could go with this. In the absence of more information it is really difficult to give good advice.

 

OK, since you show yourself as "student" this was important to ask due to AAC rules.

As far as your problem goes...

It would be exceedingly helpful to get an idea of the application. After all, this is part of your notional solution, not the problem. You may be prematurely considering it, and since you don't have experience you can help those of us who do by laying out the application so we have some context.

There are many directions you could go with this. In the absence of more information it is really difficult to give good advice.

Thanks for pointing that out. I made my account many moons ago and haven't updated it.

The system is intended to prevent the collision of overloaded trucks with low hanging obstacles. I'm looking to use infrared beams for vehicle detection as well as to get an indication on whether the maximum height clearance is being exceeded. If the height clearance is exceeded then a signal needs to be sent down the road to activate a boom gate. So with that stated, reliability and error prevention is critical.

I hope this clears up the missing context.

 

So with that stated, reliability and error prevention is critical.

Lucky you were prompted to give us this information. This completely changes the way I and others would respond. For me, it means I will not make any suggestions because I am not qualified to make recommendations that are critical to the safety of persons or property.

Hopefully you will get good advice from some people here who are.

 

Thanks for pointing that out. I made my account many moons ago and haven't updated it.

The system is intended to prevent the collision of overloaded trucks with low hanging obstacles. I'm looking to use infrared beams for vehicle detection as well as to get an indication on whether the maximum height clearance is being exceeded. If the height clearance is exceeded then a signal needs to be sent down the road to activate a boom gate. So with that stated, reliability and error prevention is critical.

I hope this clears up the missing context.

It helps a great deal.

Using wireless like for health and safety related devices is never ideal. It's not that it can't be done, but it does require attention to the application's special needs. Here are a few things that generally need to be considered.

Redundancy
Redundancy might built in to a device you could buy complete, but one way to use less expensive hardware is to use more than one instance. Redundancy can be summed up as eliminating single points of failure. The important question in evaluating a solution is "what part, if it failed, would prevent operation of a critical function".

Also keep in mind that a signal prevented by co-channel interference would be a failure as well. Since you can't control the traffic on the ISM (Industrial Scientific & Medical) band, where you will most likely be operating, redundancy might be one ways to address this.

So, in your case, you might end up with two transmitters (possibly on two different non-interfering bands), and two matching receivers. Or, you might use two pairs on a band (e.g.: 2.4GHz) where spread spectrum operation allows them to run simultaneously without interfering.

Regulatory Compliance
There are many modules readily available from typical online sources that could not be legally operated in the US (as well as some not legal in Europe, etc.). These shared bands are increasingly important and the regulations are intended to keep them operational for the community of users, so this has standalone importance.

But, even if you are a scofflaw, if you are creating a commercial product you will encounter a requirement for compliance testing. This is an extensive and detailed process and unless your device complies with all regulations, it will fail. Even if you are just a system integrator, if you sell your product you must be in compliance. The more successful you are at selling the larger your exposure and the fines for non-compliance, particularly if you become a source of interference, can be quite large.

If you are a neophyte to this area, you might be surprised to learn that just replacing an antenna on a device might run you afoul of the regulators. Devices receive certification as complete systems. In the ISM band, this includes the antenna and transmission line. In some cases there is leeway to change out an antenna with one of the same type and specification. In others, anything you might do to try to improve performance using an alternative antenna might be prohibited.

Every legal device will have an FCC ID. This can be used to find out what the conditions of certification were.

Antenna
As mentioned above, depending on your choice of device you may or may not be able to use a different antenna. The FCC and other national regulators use some version of ERP (Effective Radiated Power) when determining the maximum output of a device. This comprises the output from the PA (Power Amplifier) of the transmitter, the losses in the transmission line, and the gain of the antenna.

There may also be limits on transmission line length and antenna height above average terrain depending on the band and agency. All of these things must be considered when deciding on an antenna.

The gain of an antenna is an important specification. Antennas are passive devices so speaking about gain can be confusing. In the case of an antenna, gain refers to how much of the signal is radiated in the desired direction, or plane. Omnidirectional gain antennas are designed to focus on a certain takeoff angle. This means they will radiate most energy at an upward (good for HF band, ionospheric propagation) or a downward one (such as a mobile cell site, or a public, building mounted WiFi AP).

But for point-to-point links, like you want, directional or beam antennas are the right choice. Typical directional arrays such as the Yagi-Uda and corner relfector offer gain figures of 10dB+. Beamwidth is a major influencer of this figure, and it is proportional the number of passive radiators (called directors) in an array like the Yogi-Uda antenna.

Gain antennas offer the chance to stay within ERP regulations while make far more efficient use of the power. In a fixed, point to point link both sides can use these antennas, where permitted. But, one strategy for avoiding deviating from the permitted configuration for a given device is to use the suppled omnidirectional antenna on the transmitter and a gain antenna, possibly in conjunction with an amplifier, on the reciever, where the regulations have nothing to say.

Supervision
If this is a critical safety function, supervision may be necessary. This means that the sensor side is polled regularly by, or provides a heartbeat signal to, the controller side. If this system detects a failure, if can switch to a backup system or throw an alarm, or both—or even shut the system down if that's appropriate.

Supervision can be very simple, but it makes the system a lot safer even if all it does is warn the operator something is wrong.

Closed Loop Operation
If transceivers are used on both ends, it is possible to ensure the signal was received and, if not, to resend it. This allows the sensor to keep trying until it "knows" the controller got the message. Sometimes this is very important, particularly on marginal links. This is allied to the supervision idea.

These are some of the things to think about. More information about the distance, available power sources, location (national) and potential growth requirements for the signaling* are needed to start talking about bands of operation and specific devices. The choice to the wireless strategy could have a large influence on how many workarounds end up being incorporated and how well the system will scale.

*While I see that you said "simple binary" it is my experience that once something is in place, people suddenly find new functions they "need" from it. If you don't consider this link a datalink, I fear you will find yourself doing goofy things to add features until you have to scrap and replace it. Much of this feature creep can be anticipated if the problem space is well characterized. Considering other functions that might be demanded of the system can often lead to a choice no more, or very little more, expensive than the bare-bones option and providing that space for growth when the time comes.

 

You Tube has many videos of trucks hitting overhead obstructions, mostly on tunnels under train tracks.
They have huge and brightly flashing warning signs but the truck drivers ignore them.
Truck drivers will probably disable the radio warning system in this thread since it will probably produce false warnings and a lot of radio interference noise.

 

It helps a great deal.

Using wireless like for health and safety related devices is never ideal. It's not that it can't be done, but it does require attention to the application's special needs. Here are a few things that generally need to be considered.

Redundancy
Redundancy might built in to a device you could buy complete, but one way to use less expensive hardware is to use more than one instance. Redundancy can be summed up as eliminating single points of failure. The important question in evaluating a solution is "what part, if it failed, would prevent operation of a critical function".

Also keep in mind that a signal prevented by co-channel interference would be a failure as well. Since you can't control the traffic on the ISM (Industrial Scientific & Medical) band, where you will most likely be operating, redundancy might be one ways to address this.

So, in your case, you might end up with two transmitters (possibly on two different non-interfering bands), and two matching receivers. Or, you might use two pairs on a band (e.g.: 2.4GHz) where spread spectrum operation allows them to run simultaneously without interfering.

Regulatory Compliance
There are many modules readily available from typical online sources that could not be legally operated in the US (as well as some not legal in Europe, etc.). These shared bands are increasingly important and the regulations are intended to keep them operational for the community of users, so this has standalone importance.

But, even if you are a scofflaw, if you are creating a commercial product you will encounter a requirement for compliance testing. This is an extensive and detailed process and unless your device complies with all regulations, it will fail. Even if you are just a system integrator, if you sell your product you must be in compliance. The more successful you are at selling the larger your exposure and the fines for non-compliance, particularly if you become a source of interference, can be quite large.

If you are a neophyte to this area, you might be surprised to learn that just replacing an antenna on a device might run you afoul of the regulators. Devices receive certification as complete systems. In the ISM band, this includes the antenna and transmission line. In some cases there is leeway to change out an antenna with one of the same type and specification. In others, anything you might do to try to improve performance using an alternative antenna might be prohibited.

Every legal device will have an FCC ID. This can be used to find out what the conditions of certification were.

Antenna
As mentioned above, depending on your choice of device you may or may not be able to use a different antenna. The FCC and other national regulators use some version of ERP (Effective Radiated Power) when determining the maximum output of a device. This comprises the output from the PA (Power Amplifier) of the transmitter, the losses in the transmission line, and the gain of the antenna.

There may also be limits on transmission line length and antenna height above average terrain depending on the band and agency. All of these things must be considered when deciding on an antenna.

The gain of an antenna is an important specification. Antennas are passive devices so speaking about gain can be confusing. In the case of an antenna, gain refers to how much of the signal is radiated in the desired direction, or plane. Omnidirectional gain antennas are designed to focus on a certain takeoff angle. This means they will radiate most energy at an upward (good for HF band, ionospheric propagation) or a downward one (such as a mobile cell site, or a public, building mounted WiFi AP).

But for point-to-point links, like you want, directional or beam antennas are the right choice. Typical directional arrays such as the Yagi-Uda and corner relfector offer gain figures of 10dB+. Beamwidth is a major influencer of this figure, and it is proportional the number of passive radiators (called directors) in an array like the Yogi-Uda antenna.

Gain antennas offer the chance to stay within ERP regulations while make far more efficient use of the power. In a fixed, point to point link both sides can use these antennas, where permitted. But, one strategy for avoiding deviating from the permitted configuration for a given device is to use the suppled omnidirectional antenna on the transmitter and a gain antenna, possibly in conjunction with an amplifier, on the reciever, where the regulations have nothing to say.

Supervision
If this is a critical safety function, supervision may be necessary. This means that the sensor side is polled regularly by, or provides a heartbeat signal to, the controller side. If this system detects a failure, if can switch to a backup system or throw an alarm, or both—or even shut the system down if that's appropriate.

Supervision can be very simple, but it makes the system a lot safer even if all it does is warn the operator something is wrong.

Closed Loop Operation
If transceivers are used on both ends, it is possible to ensure the signal was received and, if not, to resend it. This allows the sensor to keep trying until it "knows" the controller got the message. Sometimes this is very important, particularly on marginal links. This is allied to the supervision idea.

These are some of the things to think about. More information about the distance, available power sources, location (national) and potential growth requirements for the signaling* are needed to start talking about bands of operation and specific devices. The choice to the wireless strategy could have a large influence on how many workarounds end up being incorporated and how well the system will scale.

*While I see that you said "simple binary" it is my experience that once something is in place, people suddenly find new functions they "need" from it. If you don't consider this link a datalink, I fear you will find yourself doing goofy things to add features until you have to scrap and replace it. Much of this feature creep can be anticipated if the problem space is well characterized. Considering other functions that might be demanded of the system can often lead to a choice no more, or very little more, expensive than the bare-bones option and providing that space for growth when the time comes.

Hi @Ya’akov ,

Thank you for your detailed response and the insight you have provided.

I will definitely be looking to add redundant power supplies / communications along with closed-loop supervision to make sure both end points are alive and talking/responding. What you say about the "simple binary" approach is absolutely true and i'm sure there are additional features that will need to be implemented down the line, so I will make sure to approach it from a data transfer perspective.

Do you have any insights on how the end-points might typically communicate? For instance, lets say I would like to use the 868 MHz ISM band. Can one just buy modules with antenna connections (uFL/SMA) and use existing 3rd party libraries to handle the transmit/receive? I suppose this is hardware dependent but i'm unsure about the interfacing of the embedded hardware with the antennae.

 

For instance, lets say I would like to use the 868 MHz ISM band. Can one just buy modules with antenna connections (uFL/SMA) and use existing 3rd party libraries to handle the transmit/receive?

Thats exactly what some of the boards you'll see on adafruit and sparkfun do. It will be an arduino with a radio module and use existing libraries to handle the communication. At least the ones that use the 433 and 900mhz radio modules. I've only done a little work with RF in these bands and thats what I started on.
WiFi/Bluetooth ones can either be the same, or the chip is smart enough where the controller with the stack is the one you program as well.
I'm beginner, at best, with this stuff. There are folks on here with a lot more experience with RF, and I defer to their suggestions before mine to be sure.

 

Hi @Ya’akov ,

Thank you for your detailed response and the insight you have provided.

I will definitely be looking to add redundant power supplies / communications along with closed-loop supervision to make sure both end points are alive and talking/responding. What you say about the "simple binary" approach is absolutely true and i'm sure there are additional features that will need to be implemented down the line, so I will make sure to approach it from a data transfer perspective.

Do you have any insights on how the end-points might typically communicate? For instance, lets say I would like to use the 868 MHz ISM band. Can one just buy modules with antenna connections (uFL/SMA) and use existing 3rd party libraries to handle the transmit/receive? I suppose this is hardware dependent but i'm unsure about the interfacing of the embedded hardware with the antennae.

Yes, you can buy MCU development boards with integrated radios, or standalone radio modules. The choice is a matter of what you would like to do. Lately, LoRa is an excellent option for working with integrated radios, and while you don't need to extreme distance abilities of LoRa, the parameters can be adjusted to up the data rate (it depends on the low data rate for maximum link budget) to optimize it for your use.

LoRa is good because if you end up with a network of these things (and you easily could), it will work very well in a mesh configuration. On the other hand, a protocol like ESPNow, running at 2.4GHz is also attractive due to its fast and connectionless nature with very low overhead since it isn't doing WIFi. A bit of design thought might help you decide.

LoRa will be more expensive than ESPNow, but if you really only have a single point-to-point it doesn't matter, and if you end up discovering you are expected to include a previously undisclosed location a mile down the road, it has a fighting chance.

 

I would choose here the good tested stable values, however them are 1000x more capable. But the main criterion I see here is price plus effort. So, take the Nordic NRF24L and everything will work for the sure. With good chance may get it for 99 cents per piece. With less luck may try the link below. Already soldered!! Contains everything You need including antenna, only the software and Arduino must be added.

https://www.ebay.com/itm/285145026909?hash=item4263f7d15d:g:VoEAAOSwlTRj6fBt&amdata=enc:AQAIAAAAwPHeJZ62c8MtPJNnwvwy4bLUO4OiW5Ibax0g8lIqTtJx7IAeP4cRt142j1HeZ9UWeYS48auYIf3bulyWCfzFPqEuTGpHPAEDmmE7hB0CGeL+XvcvuC+fhHooOn7GAmTSa3pRrkfjsWbN8r4KA0s32AvDRO7eo0+RWmRXoLm9/bNMKOV/VsG2QISVSfd79Mn0eAeJdlmqwV3kYNMGBi2YARuPew4z1Gwftv25OzyC+zUOwQbiQUv48GFONzjkOpx17A==|tkp:Bk9SR-aWk7qzYg

 

I would choose here the good tested stable values, however them are 1000x more capable. But the main criterion I see here is price plus effort. So, take the Nordic NRF24L and everything will work for the sure. With good chance may get it for 99 cents per piece. With less luck may try the link below. Already soldered!! Contains everything You need including antenna, only the software and Arduino must be added.

https://www.ebay.com/itm/285145026909?hash=item4263f7d15d:g:VoEAAOSwlTRj6fBt&amdata=enc:AQAIAAAAwPHeJZ62c8MtPJNnwvwy4bLUO4OiW5Ibax0g8lIqTtJx7IAeP4cRt142j1HeZ9UWeYS48auYIf3bulyWCfzFPqEuTGpHPAEDmmE7hB0CGeL+XvcvuC+fhHooOn7GAmTSa3pRrkfjsWbN8r4KA0s32AvDRO7eo0+RWmRXoLm9/bNMKOV/VsG2QISVSfd79Mn0eAeJdlmqwV3kYNMGBi2YARuPew4z1Gwftv25OzyC+zUOwQbiQUv48GFONzjkOpx17A==|tkp:Bk9SR-aWk7qzYg

The Nordic radios are very good. The nRF24L01+LNA+PA would be a good choice if you weren’t going to go with something integrated, and if there was no chance of needing a mesh network.

I don’t know that it would be my first choice for this application. Range when using random modules and supplied antennas is frequently a problem. It’s not the Nordic chip, it’s the implementation and antenna (often they might as well be a wet sock for the quality of the match they offer).