• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

positioning system using tones

Status
Not open for further replies.

PlaneMad

New Member
This is part of a small college project that im doing where i plan to make a simpsystem which will tell passengers inside a train what station is coming up next.

So heres how i thought it would work (the emphasis of the project is on simplicity)

Each station transmits different tone frequencies using fm. So station1 has 1KHz, station2 has 2Khz. (same carrier but different mod frequency)

In the train the tone is demodulated from the carrier and fed to a frequency voltage convertor. So now each time it passes through a station , we get a particular voltage, say 1V for station1 and 2V for station2 etc. I plan to use a total of 8 different tones, so 8 different voltage levels.

This dc voltage is converted into a digital code using a adc chip, after which it will be fed to a 3:8 decoder and light up an LED status board for the corresponding station.

I want to know if this is practicall possible to implement. we already have a tuned fm tx/rx system where we can demodulate the tone that was transmitted. im stuck at the fvc section. initially i tried building a circuit using the xr4151 ic but that didnt work. after some googling ive found that you have another simpler ic lm2917 which im planning to use. will that do the job?

im still an elec newb, so be soft on me.
thanks :)
 

Sceadwian

Banned
Sure, but you'd have to broadcast at a very low power to avoid the stations overlapping, but still be high enough to have reliable detection. Are you trying to do this with all analog/discrete components or are you willing to do something digital? Instead of transmitting tones you could use the RF to transmit location information to a micro controller. The radio should pick up the strongest station nearby. It could also be used to transmit time or 'running late' information or whatever else you want. Sorry to recommend something completly different than your current setup, but I'm a big fan of throwing micro controllers at projects, because they tend to open up a lot of possibilities.
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
This is 21st century, not the 1960's - simply use microcontrollers to send an individual digital code for each station - it could even send a complete text string that the train displays.
 

PlaneMad

New Member
haha yea, its the 21st century, but we want to do a some basic circuit learning and do something useful while at it. like i said, the emphasis is on simplicity/cost and not on practical feasability.

it will be demonstrated in the lab, so noise/ station overlapping wont be a problem. we simply plan to switch off the transmitter, change the mod freq and switch it back on to simulate the next station.

I need to get this done within a few days, and in theory looks simple enough, but im sure there might be a few design challenges in getting the whole thing to work smoothly. for starters, im not too sure about the fvc part. can i just pluck the Minimum Component Tachometer circuit in the lm2917 datasheet and expect it to give the desired output? what kind of an output voltage range do i need to drive the dac and the decoder?
 
Last edited:

user_88

Member
As far as converting from integer volt signals to LEDs, you might take a look at the LM 3914.
LM3914 - Dot/Bar Display Driver

At the of the page, there is an application circuit which almost does what you describe.
I am not completely certain, but you might be able to adjust the reference resistors ... R1/R2 ... maybe use a potentiometer, and get the circuit to work with 8 voltage intervals of one volt.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Such systems are designed to syncronise before any data is sent - check my PIC tutorials, which have both IR and Radio examples - either of which could easily do your application.
 

PlaneMad

New Member
As far as converting from integer volt signals to LEDs, you might take a look at the LM 3914.
LM3914 - Dot/Bar Display Driver

At the of the page, there is an application circuit which almost does what you describe.
I am not completely certain, but you might be able to adjust the reference resistors ... R1/R2 ... maybe use a potentiometer, and get the circuit to work with 8 voltage intervals of one volt.
awesome. so i basically need to do the frequency voltage conversion to finish it up :)

and one more thing is that the output needs to stay fixed at the last position whenever there is no input (between stations). some sort of latch?
 

user_88

Member
. some sort of latch?
good point .... have to look around for a suitable 'latch'.

Also a good idea to breadboard the proposed circuit and see what actually happens ......

I may have found a suitable track and hold circuit .... an old reference book.
If at some point you want to try it out .... send a message ... I will have to draw a rough diagram.
 
Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading

 
Top