bridge lights - a physical bridge

I would like to build a circuit to light a physical bridge built over a small stream in my back yard.

I need two strings of 20 LEDs each, to line the sides of the bridge so that people don't fall off in the dark.

I want it to be battery powered, and I want it to turn on 4 hours a night, and then shut off. Light detectors won't work in this location.

The LEDs don't need to be very bright.

It would be better if I didn't need to replace the battery every week.

Can anyone help me with this ?

There are many unknowns in your request. The first thing I would say for an application such as this I would go for rechargeable batteries - they should be good for 500 charge/discharge cycles and it would be nice to have them charge up via solar cells placed in a suitable location (on a tree?). For simplicity I would use a battery powered alarm clock to start your 4 hour timer. they are very reliable and cheap.
You don't say what sort of LEDs you are intending to use at what spacing. I suggest that you use Google and look at trade adverts for "garden lighting" until you can work out the wattage of the LEDs.
Frank

Since you have running water, it would be practical to make a paddlewheel, to turn a generator, to power your led's.

The generator can be a small motor. However if it were to run 24/7, it would probably wear out the bearings. So you might want a way to physically block it from operating outside of the 4 hours you specify.

Such a project would need the mindset of an inventor, to build it and test it and troubleshoot it, over a period of time.

Or...

Since this is similar to solar-powered garden lights, you might want to look into that technology.

BradtheRad said:

Since you have running water, it would be practical to make a paddlewheel, to turn a generator, to power your led's.

The generator can be a small motor. However if it were to run 24/7, it would probably wear out the bearings. So you might want a way to physically block it from operating outside of the 4 hours you specify.

Such a project would need the mindset of an inventor, to build it and test it and troubleshoot it, over a period of time.

Or...

Since this is similar to solar-powered garden lights, you might want to look into that technology.

Click to expand...

thanks for the reply.

this is way outside of the scope I have in mind.

the water is neither deep enough nor fast enough to work as you imagine it to be.

I am looking for a solid state solution, not a mechanical one.

thanks for the idea, though.

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chuckey said:

There are many unknowns in your request. The first thing I would say for an application such as this I would go for rechargeable batteries - they should be good for 500 charge/discharge cycles and it would be nice to have them charge up via solar cells placed in a suitable location (on a tree?). For simplicity I would use a battery powered alarm clock to start your 4 hour timer. they are very reliable and cheap.
You don't say what sort of LEDs you are intending to use at what spacing. I suggest that you use Google and look at trade adverts for "garden lighting" until you can work out the wattage of the LEDs.
Frank

Click to expand...

thanks for the reply.

re LEDs and spacing, I need 20 LEDs in each of 2 strings - 40 LEDs total. They can be normal, not superbrite. Each LED in a string will be spaced about a foot apart, and the bridge measures 3 feet wide. What else do you need to know about them ?

re power, I can use a solar panel up in a tree to recharge.

re timer, I was hoping to use an IC for that purpose. I need the timer to keep the LEDs on 4 hours each night.

I understand that there are variables to getting this worked out, but I need guidance to fix the values.

I think that I have laid out the application clearly.

I spent some time Googling information on computing LED power and voltage values, power source wattage and watt hours, and now I am more confused than ever.

I have done electronic circuit projects such as sound effect devices, but it always involved components and layouts that were already specified. Handy with a soldering iron, not so much with working out projects like this.

Let's say that I want to work with red LEDs (which I understand have the lowest voltage drop), and that I want to connect them in parallel (so that I don't need crazy voltage to get them to light up). The calculators I've seen online indicate that the current limiting resistor would be a very low value, which seems good to me, since very little voltage is wasted. Of course, like everything else, there is a tradeoff somewhere here. I just don't know what it is, yet.

So I need to know what combination of batteries, of what voltage, and connected in what way, will give me the four hour window I want, and how long, in total hours, I can expect the LEDs to remain lit, given that the batteries are fully charged.

Any more details needed, please advise.

I really don't want to use garden lighting, since that requires either an outlet or solar chargers which are built right into the devices. That won't work here since the bridge area is completely overhung with tree branches. I cannot cut the branches down.

i would go for a 12V battery. As low wattage LEDs are 2.1V @20mA, i would use 5 in a string 5 X 2.1 = 10.5V, so you have to drop 12-10.5 = 1.5V at 20 mA so the resistor will be 1.5/.02 = 75 ohms (68?). So you need 8 strings.
Now for your timer, use a chip number 4060 ( **broken link removed**) or similar for the 4 hour timer. if you use this sort of circuit for your 24 hour timer, it will work but the problems of getting the 24 hour delay exactly 24 hours will be very difficult, that why i said use an alarm clock! One solution might be to use a crystal oscillator and divide it down (making your own alarm clock?) such as :- https://www.brighthubengineering.co...83-build-an-illuminated-hi-end-digital-clock/
Frank

Taking Chuckey's recommendation as a springboard, here is a simulation.



I assume you want the led's to light at dusk, so I put a photosensor and schmitt trigger as the input.

I drew 'black boxes' to represent the complicated functions.

To illustrate what goes on in the 4060 counter IC, I used a separate pulse generator and frequency divider.

You would tap from the divide-by-2048 pin (give or take), and adjust the oscillator to yield a 7 second timed output.
That will give you 14,336 seconds (4 hours) of 'On' time for the led's.