How to find a right RF module for a project?

[rushi121]

I am a product developer but not an electronics engineer. I am doing a cost analysis of a product idea for my company. The product will need something like this...

There will be two small portable devices (A and B) 1 meter apart (not in line of sight since A can be in pocket). Product A will keep pinging product B at regular intervals. When pinged, B will send response to A for that ping. A knows that B is still available.

Now, if we move B away from A (e.g. > 3 meters) and if A pings B and since B is out of range, A will not get response from B. In such case A will sound an alarm.

I know we can do device to device communication using RF modules. But I don't know which module or protocol to use for this.

My questions (Please answer considering that I am not prototyping but actual product for market):

• Which protocol and module to use?
• Can you point me to any module available in market that I can look into?
• Since A will be pining B at regular interval, will that module drain battery much? If yes, how much long will battery last approximately?
• Any existing product in market you can think of that does something similar (pinging at regular intervals)?
• Do I need a micro controller?

 

[berkeman]

I am a product developer but not an electronics engineer. I am doing a cost analysis of a product idea for my company. The product will need something like this...

There will be two small portable devices (A and B) 1 meter apart (not in line of sight since A can be in pocket). Product A will keep pinging product B at regular intervals. When pinged, B will send response to A for that ping. A knows that B is still available.

Now, if we move B away from A (e.g. > 3 meters) and if A pings B and since B is out of range, A will not get response from B. In such case A will sound an alarm.

I know we can do device to device communication using RF modules. But I don't know which module or protocol to use for this.

My questions (Please answer considering that I am not prototyping but actual product for market):

• Which protocol and module to use?
• Can you point me to any module available in market that I can look into?
• Since A will be pining B at regular interval, will that module drain battery much? If yes, how much long will battery last approximately?
• Any existing product in market you can think of that does something similar (pinging at regular intervals)?
• Do I need a micro controller?

Sounds like a good fit for Bluetooth Low Energy (BLE): https://en.wikipedia.org/wiki/Bluetooth_low_energy

 

[meBigGuy]

Number of issues:

1. What happens when other pingable devices are nearby
2. How precise do you want the distance
3. Do you want sender and receiver factory paired? Can they be re-paired to different devices?
4. Is there any significant data transfer beside the ping.

One issue with bluetooth is that the pairing process is never simple and can be problematic.

One of the big problems is designing a timed protocol ( synchronized timing windows) such that the devices know when to turn on to ping. If the receiver is on all the time that is way too much power.
You will definitely need a microcontroller based solution for a robust commercial solution. The controller can be in the RF chips (depends on what you really want to do)

Bluetooth may be overkill. More suitable might be the chips like those used in wireless mice.
Anyway, these guys build Bluetooth and very low power non-bluetooth and their sales/applications support should be able to help you decide.
http://www.nordicsemi.com/eng/Products/2.4GHz-RF

 

[Tolklein]

With RF anything over a few 100 millimetres you would be looking in the UHF range, and there are certifications that need to be considered depending on your target market countries.
This type of system is often used, in reverse I suppose, in mining environments where personal and small vehicles would carry transmitters, and larger mining vehicles would carry receivers with alarms to alert them when there are people about. They're generally marketed as "Collision avoidance systems"
In your case the person would carry the buzzer part and receiver, while I'm not very familiar with the electronics side of it, I think you may struggle to manufacture a pocket sized receiver, unless it has a little aerial sticking out.

 

[rushi121]

One of the big problems is designing a timed protocol ( synchronized timing windows) such that the devices know when to turn on to ping. If the receiver is on all the time that is way too much power.

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For timed protocol I will turn on and off pinging based on a switch. It won't be on most of the time. But I was thinking about how BLE Beacons work and they continuously ping and battery last from 6 months to 2 years. Can't we do something similar or are they something special?

 

[meBigGuy]

BLE can probably do what you want, but I don't know the subtleties of pairing, and I don't know know your real requirements in that regard.
You should talk to Nordic, then TI.

 

[meBigGuy]

This might be a good place to start.
https://www.nordicsemi.com/eng/Products/Bluetooth-Smart-Bluetooth-low-energy/nRF51822-Bluetooth-Smart-Beacon-Kit

But, be sure to understand the heck out of the pairing issues before you start.