Automatic & manual Headlights alarm circuit with LDR

[csordo]

I'm having a little trouble trying to modify this circuit I found online to make it work with a LDR (simulated with potentiometer), I almost got it working the way I want it. OK... here is the scenerio:

1. Turn on the engine in the car (switch S2) turns on the motor (LED2)

2. As the sun goes down and gets darker, the LDR (potentiometer) automatically turns on Headlights (LED1)

3. we can optionally turn on manually the headlights with switch (S1)

4. If we turn off the car and forget to turn off the headlights manually, the alarm (buzzer) sounds.

The only problem is that if the potentiometer is active (dark or night) and we do not turn off the lights manually, it also turns on the LED2 (motor). This would means that if is dark outside, the car would turn on... which is obviously a big problem.

[Fernando_D]

Hi,

What I see is that even though S2 is open the current is finding a path through S1. How does the original circuit look like?

Regards,

[csordo]

The only difference from the original circuit is the portentiometer. I placed the potentiometer to simulate a Light dependent resistor (LDR). If you take out the potentiometer, then you will have the original circuit. It almost works the way I want it to, but like I explain before "If it dark outside the LDR will be activated, plus I forgot to turn off the switch S1 off manually, the LDR will turn on the motor (LED2) as I said before a big problem. 

Thanks for your help

[Fernando_D]

Hello,

As I mentioned, in this scenario the current is finding a path to LED2. So here is my suggestion: use a diode to block the current.

Furthermore, with this configuration the alarm also goes off to alert the user that the headlights are on. Note that I decreased the values of R4 and R6 so that they can activate the LEDs. Also, the 1N4001 is a common diode, but you should do further research to see if there are better options.

I also attached the circuit, hope this helps.

[csordo]

It finally works... thank you. I had explored other options and I've been told it can be done with a 741 op amp, but I want it to do it with the most basic and the least amount of components as possible. It is for a school project; where the requierement was to use limited resources.