Automatic Street Lighting project

Hi All,

I am currently working on a project for which need some guidance. Just to make sure I am on the right track.

The project details

I did a prototype on a breadboard with an ATMEGA8 chip ( i had an old board and frankly wanted to keep my arduino uno away from 240V supply). Anyhoo moving forward, Cricuit is simple attaching an LDR to one of the input pins of arduino, reading it and when the light is low turning on a relay which is further driving a 100W bulb and vice versa. Everything is working dandy. I need to make this as economical as possible, so using a cheap atmega8 chip with ldr and relay ( 6v simple operational one). My design includes keeping atmega8 and relay at the base of the Street Light Pole while the LDR circuit or sensor will remain above the Street Light bulb ( to prevent any light seeping in and turning off the ldr). I will be connecting them with simple cables. Power to circuit will be provided via transformer/adaptor and the main street light circuit will be controlled via relay. Per resources available to me everything can be done within 5-6$ budget , which is good.

So well , feedback plz how does this sound?
Anything I can do to improve the design . I have seen circuits which does not include any atmega chip just controlled using npn transistors, which one is a better design ?
Are there any drawbacks of this ( i.e. using LDR to control light ).

thanks for your help.

Using an Arduino to read the LDR and switch the relay is convenient and easy, but involves some relatively expensive hardware. Much cheaper, simpler and more reliable solutions would be achievable just using analog electronic circuits to apply a threshold to the LDR reading and turn the lamp on and off. Since you mention economy I guess you may be looking for wide scale deployment and the unit cost will be important. In that case I would have thought the analog approach would beat the Arduino approach by a huge margin. In fact you can already buy lamp holders with this capability build in, for less than the cost of an Arduino (I have a couple of them). Is it actually economically sensible to build your own?

Hi Thanks for the reply. Actually it has to be an add on rather then new bulbs/fitting etc as cost will increase with any new purchase. As far as buying circuit and experimenting with it ,I haven't found anything that is ready to use to fit the requirement , once that are available like from L&T , GE etc are pretty expensive.

You could save a buck or two by using an ATtiny instead of ATMEGA8. The ATtiny85 would work easily, but the ATtiny13 would be slightly less expensive. If you really wanted cheap, you could use an ATtiny10.

dr_watson:
Hi Thanks for the reply. Actually it has to be an add on rather then new bulbs/fitting etc as cost will increase with any new purchase. As far as buying circuit and experimenting with it ,I haven't found anything that is ready to use to fit the requirement , once that are available like from L&T , GE etc are pretty expensive.

What's your budget per unit, and how many of them do you envisage producing? You seem to be describing street lighting systems but 100W is obviously not sufficient for that and the sort of approach you're describing does not seem remotely feasible for that sort of thing. Is this to control some private security lights, or something? In that case, don't you just need a single controller, probably timer-based?