Hello again, dusk sensor project

Hi,
I posted on here a long time ago with my idea for a circuit I wanted to build, someone kindly pointed me to a couple of diagrams which I tried to build on breadboard but could not get to work, then I got side tracked and the idea was shelved for a while. I got all the parts from Maplin which was cheap except the breadboard.

I have now returned to trying to build this and would like some help if possible.
I am a complete novice as I have not done electronics since school so please treat me as a child.

My project is as follows:-
I want to have a bank of 12v 1.1w led bulbs powered from a car battery which is switched on at dusk, but the duration of the lights being adjustable due to seasonal requirements, Eg longer in the winter etc.
My thoughts were a dusk sensor, which when energised (eg goes dark) would power a timed on circuit which in turn would energise a relay. The timer would be adjustable via a pot. Hope that is the right word.
The circuits could also be powered via the 12v car battery.

Hope that makes sence.

I want to get this on a bread board and get it working before I take it across to strip board etc.
Any help would be great

Dickspanner

night detector

I did this about 20 years ago. It requires less than 4 square inches of board space and does a good job of ignoring interference, like passing car headlights. The timer chip is programmable with dip switches. The output is a light flasher with a 10% duty cycle...one tenth of a second per second if I remember correctly.

Anyway, it can give you ideas.

Wow, that looks fantastic, a lot more complicated than my previous attempts.

Here comes the first of probably many stupid questions in relation to the diagram,

I presume the triangles are 0v are these just to be connected together? Told you I know nothing about electronics.
What does your last statement mean about duty cycle?
Is there no relay required to switch the lights on and off?

I am good with AutoCAD so I will start to draw this circuit as I did with my last scheme to ensure I understand it and it will also allow me to make a compoanant list as well.

Thanks for the diagram and I will start my project again.

Dickspanner

It's a lot more complicated because it works. I spent a week researching light levels, designing, and building. The CDS (cadmium sulphide photocell) is peculiar to this design. It's the one I had laying around, and I have no idea what its part number is. Some Radio Shack junk from the '70's. You'll have to buy one and change the (3) 680 ohm resistors to suit the one you buy. Whatever resistance your photocell has at sunset is the value of the resistors.
The triangles are operational amplifiers. a quad of them in one package. The part number is on the lower left of the drawing.
Duty cycle means on-time compared to total time of a complete cycle. The light bulbs are fired with a 3 stage transistor amp. It's a lot more complicated (predictable, adjustable) than hobby level because it had to work in Las Vegas.

Hang on...I just figured out you were talking about the triangles that point downwards. Yeah, those are ground symbols.

How long of adjustable time ON

The posted circuit seems a little overkill but then that depends on duration of desired time ON
My first idea was just a simple dusk detector
LM741 Light Dark Sensor Circuit - Electronics
then perhaps a simple adjustable 555 but maybe not long enough time ON
A 555 connected to a 4017 for longer time but how long desired?

The "time on" for this configuration is 30 minutes. It's caused by the "clock" components (RC for the oscillator in the timer chip) and which pins are grounded. The inverter transistor also has something to do with timing. One good point is that it has been built, tested, and works for a living. No bugs. I forgot so much about this circuit, and didn't expect anyone to copy it verbatim, but you can look up LS 7210 to figure out how fast the clock runs and how many counts I programmed to get to 30 minutes.

ps, that 741 circuit will detect darkness, but it will change its mind every time a car shines headlights on it. My circuit requires 20 seconds or so of "night", then latches the sensor out when it starts counting. It will not restart until daylight happens and dusk happens again. One of the "advantages" of overkill is that every function can be changed by changing the value of a resistor, capacitor, or the grounded pins on the counter.

Ps, again...The LS 7210 chip provides the oscillator (555 function) and the counter (4017 function) in one package. I don't expect anyone else will want a 10% duty cycle, incandescent light bulb flasher, but it's all negotiable due to the overkill.

I am going to CAD up the design and post it back up for comment later.

I will go to Maplin this weekend and get all the parts to hopefully have a play to breadboard it.

Dickspanner

I might remember...I think this timer chip detects dusk, waits for some period of time, then turns on and flashes the lights for 30 minutes. That would explain why the inverter transistor is attached...it changes the time that is counted out because the "wait" time is different from the "on" time.

In answer to the question about a relay, this timer chip has its output connected to the 10% oscillator, which drives the current amplifier transistors, which power the 6.3 volt light bulbs. You can easily eliminate the 10% oscillator and 6.3 volt power stage, then add enough transistors to power a relay.

I pretty much optimized this circuit for low power consumption. That's why the 47k resistors are in the Wheatstone bridge section...to lower the current consumption during the 23+ hours that the lights are not on. They also provide a voltage reference at about 1/2 the supply voltage so the second and third op-amp have a voltage to compare things to.

It is not mandatory to use the 20 year old op-amp chip (LM346). I'm sure there are better op-amp chips available today. I am not sure the LS7210 is still available. You might have to use the 555 and 4017 route that MrDEB mentioned in order to be able to buy the parts you will need.