scenario:
"Sensor" arduino has 3 sensor values of interest.
"Master" arduino needs to ping the sensor and retrieve the 3 sensor values and also calculate the distance to the sensor.
This will be a "line of sight" distance ranging from 30 feet to 150 feet. Measurement resolution of +- 1% should be sufficient and would get within 3 inches at 30 feet and 18 inches at 150 feet. I could even go as loose as 2% resolution.
For the sensor data, Bluetooth class 1 is probably an option, but it is way overkill in power required, cost and functionality. Even XBee would seem to be overkill.
I'm thinking more of a garage door opener than a true network, but I would "mate" the two arduinos to minimize interference with similar devices.
For the distance measurement, would it make sense to use ultrasonic on both ends and measure the "echo" time? I thought of using echo time of an RF signal, but the speed of light thing makes it hard to get nanosecond measurements on an Arduino (light travels roughly 1 foot per nanosecond).
To give you and idea of frequency... Once a day or on demand, (say once every 5 minutes over the course of an hour), the "master" would ping the "sensor" 5-10 times over a span of 2-5 seconds to ensure stability of readings and distance measurement. So around a total of 200 pings per day.
Bottom line: I need a cheap RF network and a 30-150 foot range finder between two arduinos... how would you solve this?
The cheap RF network is easy -- you can buy them. However, the 30-150 ft, 1% electronic distance measurement is extremely difficult, if not impossible, on a hobbyist budget. The topic comes up every few days on this forum, so you might look through the discussions to see why.
electronic distance measurement is extremely difficult, if not impossible
Sounds like a commercial opportunity (LOL) !!!!
3 inches resolution is 7.62cm = 0.0762m, and radio waves travel at approx 300,000,000 m per sec.
So that would mean that the OP has to resolve the ping time delay to 254 pico seconds by my maths !!
(clock freq would need to be just under 4GHz)
Bottom line: I need a cheap RF network and a 30-150 foot range finder between two arduinos...
how would you solve this?
I wouldn't .And niether will you. If you can get a hunting rifle laser range finder with computer output it would be doable but without that , forget it. IF you can get a military grade or surveying grade distance sensor with computer output it shouldn't be a problem, but it won't be cheap either. I suggest you choose another project because your chance of getting this to work without the above is slim to nil.
It's not going to happen. Ultrasonic is out of the question. I shouldn't have to explain why. (ie: for $120 you can get 10 meters range. )
Thought I would ask since you guys know a bit more than me
.
I had hoped that since both ends of the measurement are arduino based, that some technique would emerge that makes it possible (hence the ultra-sonic thought since it would be one arduino responding to another arduinos ping with its own response ping instead of a simple rebound off an unknown object)
.
And I'm not opposed to building a specialized device to do this with a much faster CPU to get to the nano-second for radio-echo timing, but I obviously was wanting to avoid that.
.
Thanks for the thoughts and chime in if you think of something else.
If you're still talking abiut ultrasonic then you didn't pay attention. Ultrasonic has a maximum range of 10 meters , which is 120 feet short. Survey equipment has more than enough range as well as do the sniper range finders used by the military but they don't have
computer output. If you can find a laser version of a Tape measuring device but with computer output that would work. The one I found uses Windows app to display the distance which won't work for you. If you liook you might find what you need, or not.
(LOL) !!!!