I've come up with an idea to make a seeking device:
one rf transmitter transmits 10 different signals with 10 different voltages being supplied (in sequence).
one receiver interprets the received data and lights up the corresponding leds meaning that the closer you get to the transmitter more leds will light up
Problems:
i'm really really new to this electronics thing so its very hard to go from concept to device.
the transmitter gets its maximum range at 12v and the arduino works at 5v (and it isnt possible to use pwm for serial?)
Possible solutions:
i'm willing to learn...hopefully someone is willing to teach
2.1 my first guess was to use a serial controlled digital pot but have had a hard time finding the best one. The ones i find only work up to 5v
2.2 using 10 different pins to transmit with different transistor/resistor combinations in each (is that even possible? seems unnecesserally complicated to me vs the digipot solution)
2.3 ok...this one is just to demonstrate how basic my electronics knowledge is: if nothing else works i'm willing to try connecting a servo to a physical potentiometer! ;D hopefully it doesnt get to that!
Sorry this won't work as the signal received in practice will not vary nicely and proportionally with distance.
What will happen is that there will be reflections of all the surfaces of your room causing the signal strength to be not proportional to your distance.
This technique can be used in multiple mesh network devices but here you are taking an average of several transmitters. An this works at frequencies of a few GHz. I think the transmitter you are thinking of uses about 400MHz.
Anyway basically you don't change the transmit power but you monitor the AGC (automatic gain control) voltage from the receiver.
hummm...not totally convinced it won't work. Let me try and explain better:
This is to be used in an open field (one tree here and there but mostly open field) so the reflection issue might not apply.
The receiver is walked around by a human if that matters so accuracy isnt critical: just 10 steps of closer/farther to the goal indicated by the number of leds. Humans are better interpreting those ocasional randomly blinking leds i hope.
The transmitter is 315Mhz and the applied voltage can go from 2v to 12v for a range of 0-150m. So the concept is:
Voltage apllied Message Distance (supposed)
2 A 1m
3 B 5m
4 C 10m
5 D 20m
6 E 40m
7 F 60m
8 G 85m
9 H 95m
10 I 115m
11 J 135m
12 K 150m
The idea is to do that sequence every 2 seconds+- so the receiver would only light one led at 150m and all 10 led next to the transmitter.
As i said accuracy is not a problem. I just dont know how to make that work. Like what components/circuit to use.
Can someone help me with that so i can prove myself wrong?
basically you don't change the transmit power but you monitor the AGC (automatic gain control) voltage from the receiver
You´re suggesting doing on the other end right? The way i conceived it seemed theoretically easier. Can you elaborate on the AGC control solution? Thanks for the reply.
It would be easier for you if you chose a system where the receiver had a relative signal strength indication (RSSI) output. This provides an indication of the received signal strength and you may be able to use this to determine distance if nothing is causing signal reflections.
I don't think there is an RSSI output on the sparkfun 315mhz module although there may be an signal on the smd receiver chip if you can get at it.
many of the 2.4mhz systems provide RSSI information, although thee devices are more expensive than the one you were looking at.
I am a radio ham and have been involved in fox hunts for many years. These are where a radio transmitter hides and people try to find him by taking radio bearings. When you are close it it is very difficult to get a directional bearing even in the open air. This is due to two facts, first it is impossible to get a fully isotropic antenna (that means not directional one) therefore the angle you hold the aerial at has a strong effect on the signal received. Second as you close in you get the effect of nulls and peaks as you pass through intrigal number of wavelengths away from the transmitter. At the frequencies you are looking at this wavelength is about one and a half meters.
Thirdly (no on expects the Spanish Inquisition) you have the soggy mass of water that is a human getting in the way and attenuating the signal.
Turning the voltage down on a transmitter is the easy bit if you want to do it. You just use a variable voltage regulator and feed a varying signal into it. This can be derived from the PWM output passed through a low pass filter (capacitor).
he way i conceived it seemed theoretically easier.
Not really measuring the signal strength at the receiver is easer, plus the transmit power will not increase linearly with voltage.
Yes, I did mean Ghz. And at that wavelength I do think it would be interesting to playing with the RSSI signal as a rough distance detector. But as mike says, it will be affected by the type of antenna and proximity of the user.