Lighting driver unit: traffic lights

dl324

Joined Mar 30, 2015
16,989
Welcome to AAC!

As this is schoolwork, you need to post your solution to part 2 and your attempted solution to part 3.
 

Thread Starter

Letho

Joined Mar 8, 2024
5
I decided to go back to school and finish my degree and woah this is what I found. I am only responsible for subsystem 3. For now im trying to find out how to interact with the other subsystems. Im not sure if my thinking is correct here. This is a block diagram of what I have so far.
 

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Jerry-Hat-Trick

Joined Aug 31, 2022
574
Congratulations for being picked to do the most difficult subsystem! Initially I wouldn’t worry too much about interfacing with subsystem 2, there will be inputs you can process from that. And it looks like you’ll have a 5V supply from subsystem 1.

Breaking the project down, you need a way to sense the ambient light level and to have an output which changes state at a given level with some hysteresis, you need to control the brightness of a mains incandescent bulb with a triac and a way to get 60% brightness.

Google search those three and have a go at posting your findings. There are actually threads on this site that will help you!
 

Thread Starter

Letho

Joined Mar 8, 2024
5
So what I’ve found so far is I should connect the input of the light sensor to the power supply and connect the output to an optocoupler which is connected to a triac plus a diac to switch from dc to ac. The voltage from the sensor as soon as the sensor detects ambient light should allow max voltage to lamps and the voltage at no light detected should allow 60% of the voltage through a diode clipper. Am i in the right direction. And also how do i set the hysteresis ??
 

Jerry-Hat-Trick

Joined Aug 31, 2022
574
Let’s focus on the light sensor, what component options are there, and how would you connect it using the 5V supply? Also, how would you process the signal to get an output which swings from rail to rail at a selectable brightness with hysteresis?
 

Thread Starter

Letho

Joined Mar 8, 2024
5
I am using a basic ldr in series with a resistor connected to a comparator. The ldr is connected through a wire with the positive terminal of sub1
 

Jerry-Hat-Trick

Joined Aug 31, 2022
574
I am using a basic ldr in series with a resistor connected to a comparator. The ldr is connected through a wire with the positive terminal of sub1
Okay, how about posting a neatly drawn schematic, photo of pencil sketch is fine, showing how you would connect a potentiometer to vary the high/low LDR voltage and how you would achieve hysteresis and how you would vary the hysteresis window? Ideally, show suitable component values based on a specific LDR
 

Thread Starter

Letho

Joined Mar 8, 2024
5
If i use R3 as a potentiometer I can vary the ldr voltage. And i can change the husterisis window by changing the ratio of R1/R2. Am i in the right direction?? I haven’t been able to choose an a specific ldr yet
 

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Sorry, but this is not right.

Maybe you should google how comparators work. Basically, there are two inputs, plus and minus. When the positive input is a higher voltage than the negative input the output swings to the positive supply rail, and vice versa. So you need to have the LDR in series with a resistor as potential divider betwen the positive and negative (ground) supply rails with the centre point connected to one compartor input with a potential divider whose centre point goes to the other input. The output will swing between the supply rails when the plus/minus inputs cross over. Adding hysteresis requires the addition of another (feedback) resistor - google how that works, I can't do it for you. And you really should start by selecting a suitable LDR and a suitable comparator, so you can select suitable resistor values.

Forgive me for saying, but this is very basic electronics and I would recommend you have a serious discussion with the project mentor who should not be expecting you to start working on anything mains voltage related if you are struggling at this stage.
 
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