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Author Topic: Viability: Day visible Led + solar powered + zigbee  (Read 1084 times)
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Hello. I am completely newby to this forum, so I hope that my explanation is clear enough.

I am considering to build a project that consist in several devices. Each one should have these characteristics:

- led signal that must be visible either by day or night from 100m / 300ft. Light will be on for 5 seconds and then off for one minute (more or less).
- solar powered with battery bakup in order to work throughout the day
- zigbee or other wireless communication in order to alter the sequence  in which the different led signals turn on and off, duration of the cycle, and monitor device status. Each device will be 100m apart from other.

There also should be a central node in order to gather data from the led signal nodes and send it via gsm/gprs.

- Is it technically feasible to build the system?
- Will solar panels + battery be able to keep the system alive and running?

Any help / advice / recommendation would be really welcomed.
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- Is it technically feasible to build the system?
Yes.

Quote
- Will solar panels + battery be able to keep the system alive and running?
If you choose the right ones, yes.

Quote
Any help / advice / recommendation would be really welcomed.
Clarify your requirements. Are these devices going to be 100 meters apart in a line? How many of them? Bi-directional communication or uni-directional? How much data will be sent? How often? Can the XBees sleep to reduce power consumption?
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Thank you very much for your help. I am relieved to hear that the system is feasible.

Te devices will be placed 100 m apart in a line along the edge of the entry path of a farm. Total length of the road is 800-1000m, so there will be 8 to 10 led/xbee units plus the central node at the house to control them.

I have considered communication to be bidirectional:
- central unit to led nodes: Change/reverse pattern, speed, and synchronize all units. Guests walking along the path should see a light traveling from one node to the next along the path.
- led nodes to central unit: monitoring possible failures, low battery...

So, xbee communication can have very low rates: for instance 1 status message each hour, and 1 synchronization message each hour or each day if RTCs are in the different units are stable enough. In order to save power and allow smaller and cheaper batteries and solar panels the system should be sleeping as much as possible. Since there are many led nodes, each price reduction will be multiplied several times. It is a hobby project and it should not cost a fortune.

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You will need to size the solar panels to cope with the worst case daylight conditions. If this project is going to be in use all year round then the solar panels may end up needing to be quite big. If you can avoid the need for daylight visible LEDs and avoid running them all day, you would reduce the power requirements (and resulting costs) quite significantly.

I recommend that you design in an easy way to replace or recharge the batteries (perhaps by taking a 12V car battery out to your device and plugging it in for a few hours) in case your solar charging system isn't up to the job.

You will need to weather-proof everything, and from my point of view the hardware seems likely to take a lot more effort than the software.

If the intent is to guide pedestrians then perhaps you'd want to reduce the flash interval and length so that they aren't left in the dark for so long.

You may be able to reduce the hardware costs and complexity considerably by having more light units, so that they are close enough together to make use of cheap radio transceivers such as the nRF24L01. This would enable you to do the timing/scheduling centrally so that only one unit would need an RTC, and no units would need a zigBee.

Assuming you need a user interface of some sort, you would need to provide the master node with your RTC, GSM interface or whatever other method you wanted to use to access these. If it's GSM then of course you will need to maintain a GSM service too. The easier approach would be to connect an Arduino with radio transceiver to a laptop and stand next to them while you reconfigure the master node by text commands.
« Last Edit: January 23, 2013, 08:37:45 am by PeterH » Logged

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so there will be 8 to 10 led/xbee units plus the central node at the house to control them.
The series 2 models act as either end devices, routers, or coordinators. There can only be one coordinator per network, no more and no less. There is no particular advantage of a device being an end device over being a router.

So, every node, except the coordinator should be a router, meaning that each one can send data and can forward data from other nodes farther away.

The cheaper radios don't do routing, and getting one of them to transmit up to a kilometer is a non-starter.
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