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Good choice. Zigbee would be perfect, and you can poll at any time for the status.
You may need some microcontroller knowledge to use this however (I'm only familiar
with the Jennic modules - maybe there are some that require less 'interfacing'?).
I think you're saying that you want an indication that the transmitter is ok.
You could achieve that by connecting a battery directly to the transmitter. The transmitter has three pins - GND, +ve and INPUT.
Connect a 555 circuit to the INPUT pin. See **broken link removed**for a circuit. You want to use the 'astable' circuit on that page. This circuit generates pulses.
Now the circuit is continuously sending RF pulses, so you know that the transmitter is ok.
You could get a resistor (lets call it R3) and place it in parallel with R1 in that astable circuit.
Your detection wire would form part of this new resistor connection.
It will change the frequency of the pulses. If the wire breaks, then effectively R3 becomes
disconnected, and the frequency changes.
So, you have an indication that the transmitter is ok (if the transmitter fails, you will
get no pulses), and you have an indication that the wire is ok (if the wire fails, you will
get a different rate of pulses).
The thing you need to concern yourself with is power consumption; are the screens intended to last for hours or days or weeks?
If you're transmitting pulses rapidly, then the battery will not last long.
You may wish to transmit (say) a short train of pulses every 60 seconds, or every 5 minutes.
That is a more sophisticated circuit. At least the simple 555 and transmitter circuit is a 'proof-of-concept'.
The more sophisticated circuit would need to be designed to consume less power when it is not
transmitting, and transmit less frequently.
The screens are intended to last around 6 months or so. The wearing is so less that it is purposeful to check their status weekly or twice in every week. Also, since it is desired to embedd a small battery to supply the power, please suggest which battery should be used?
Further, the link to the circuit leads to an empty page. Please post another link. Thanks
The simple tx/rx circuit is only good for a proof-of-concept (maybe good enough for your project), and you would not
be able to use it with multiple screens.
For that, the circuit and software is more complicated, and you'd need to use something like Zigbee which can identify
individual nodes. This needs some software written on a small microcontroller (search for AVR or PIC), which would
connect to the Zigbee modules, which are transceivers.
You'd use a zigbee module on each screen, and one for monitoring all of the screens.
Now you can get some development kits which come with instructions, but they are a little expensive - Jennic has
a dev kit with I think 4 modules, but it is about 300dollars from memory.
Individually, a zigbee module is low cost - maybe 20 dollars or far less in qty.
You could buy individual modules and a low cost microcontroller development board (for another 20 dollars).
There is some learning curve, but as a mech eng student I'm sure you'll pick it up relatively quickly.
I think by brainstorming you could find different ways to achieve what you want, but unfortunately you may need to do that based on your knowledge of these screens. For example, if they are inserted in a specific holder, then there could be contacts on the holder to allow you to put all the embedded wires in (say) series, so that you get a single indication if any of the screens are faulty, and then rely on just a single transmitter.
In general, if you have a problem of identifying via radio one of multiple nodes, then Zigbee is possibly one of the more low-cost methods of doing it. Lower cost would be to use the simple tx modules from ebay that I mentioned, but the communication is one-way, and you could only identify them if they transmitted at different times, with (say) a different pulse rate, or an encoded value. That may be possible if they are designed to transmit at a random period.
Since you don't need such a frequent update, them the simple module method would work, if you wish to have a transmitter in each screen. In that case, use a simple microcontroller (e.g. a small AVR/PIC) to transmit a code at a pseudo-random time (e.g. approximately daily) using the tx module, so that it is unlikely to clash with any of the other screens.
If the receiver doesn't get a response from any of the screens for a couple of days, then you know that the screen is faulty.
In single quantities, a small AVR is a couple of dollars, plus a few for the tx module.
If you want to get started with AVR microcontrollers, use a guide such as**broken link removed**. (Or use a PIC, it really doesn't matter).
Your transmitter INPUT pin would be connected to one of the microcontroller pins, and the code you write would pulse the INPUT pin so that the transmitter
turns on.
At the receiver end, you'd use a receiver module, and connect the OUTPUT of the receiver to a microcontroller.
I think by brainstorming you could find different ways to achieve what you want, but unfortunately you may need to do that based on your knowledge of these screens. For example, if they are inserted in a specific holder, then there could be contacts on the holder to allow you to put all the embedded wires in (say) series, so that you get a single indication if any of the screens are faulty, and then rely on just a single transmitter.
In general, if you have a problem of identifying via radio one of multiple nodes, then Zigbee is possibly one of the more low-cost methods of doing it. Lower cost would be to use the simple tx modules from ebay that I mentioned, but the communication is one-way, and you could only identify them if they transmitted at different times, with (say) a different pulse rate, or an encoded value. That may be possible if they are designed to transmit at a random period.
Since you don't need such a frequent update, them the simple module method would work, if you wish to have a transmitter in each screen. In that case, use a simple microcontroller (e.g. a small AVR/PIC) to transmit a code at a pseudo-random time (e.g. approximately daily) using the tx module, so that it is unlikely to clash with any of the other screens.
If the receiver doesn't get a response from any of the screens for a couple of days, then you know that the screen is faulty.
In single quantities, a small AVR is a couple of dollars, plus a few for the tx module.
If you want to get started with AVR microcontrollers, use a guide such as**broken link removed**. (Or use a PIC, it really doesn't matter).
Your transmitter INPUT pin would be connected to one of the microcontroller pins, and the code you write would pulse the INPUT pin so that the transmitter
turns on.
At the receiver end, you'd use a receiver module, and connect the OUTPUT of the receiver to a microcontroller.
Thanks for the help all the while!
Having read all this, could you please formulate a step by step procedure on how to install the whole thing. Wherever learning or programming is required, please mention that. After reading all the above posts, I have got a bit confused on which equipments to proceed with. It would certainly be a great help to get a proper action plan. Thanks again.
The guide I mentioned has complete step-by-step on writing code and programming it, including screenshots.
However as tpetar mentioned, there is a cost in time, effort, and number of modules needed! if you want to have a separate
transmitter per screen.
This is something I can't really help with, you need to figure out if you really need a transmitter per screen, or if you can
somehow (e.g. contacts on the screen holders as I mentioned) to have all screens sharing a single transmitter.
Regarding transmitters and receivers, zigbee are great, but there will be a learning curve on this - not particularly high for
a uni student, but it depends on how much time/effort you put in.
The simpler (non-zigbee) transmitters/receivers have less of a learning curve, but if you want a transmitter per screen then
you'd need to make them transmit after a random interval like I mentioned possibly. Or maybe you can devise a different
scheme based on your knowledge of how the system will get used in practise.
If you're a mech-eng student, maybe a proof-of-concept on the electronics side is sufficient, and in that case maybe a
single simple transmitter and receiver is sufficient, if you are just demonstrating a single screen.
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