Hi all,

Need to transmit a simple rising edge signal over a distance of around 2km wirelessly. Zigbee doesn't have the range, neither does wifi or bluetooth. Looked at GSM but looks complicated. It's basically to show when a soapbox has crossed the finish line of a course to give a 'go' signal back at the top of the course. RF maybe, but what and how? Any ideas?

 

Isn't that what smart phones are for?

 

What is the time accuracy needed for sending the signal?
Does the receiver need to know precisely when the car crosses the finish line?

 

The 'go' signal just sets a traffic light signal to green back at the start of the course to tell the next kart to go so timing accuracy not critical. Needs to be automated though so smart phone not really suitable.

 

What about LoRa?
https://www.semtech.com/lora/what-is-lora

Can achieve some impressive ranges, obviously dependent on terrain, obstructions etc.
https://www.mesh-net.co.uk/lora-line-sight-range-test/

 

You might try an inexpensive remote relay control such as this.
You would have to hack into the transmitter to get at one of the buttons, if you want it to automatically respond to a signal from the finish line.