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Step 4Making it a nightlight
Enough with simple blinking! We want it to work at night, and stay off during the day!
Alright, let's do it.
We need a few more components for this step:
- A photoresistor (sometimes also called an optoresistor)
- An NPN transistor (most any will do. I can't even read the label on the one I picked, but I was able to determine it's NPN)
- A resistor
A photoresistor is simply a resistor that changes it's value depending on how much light is applied. In a bighter setting, the resistance will be lower, while in the dark, the resistance will be higher. For the photoresistor I have on hand, the daylight resistance is about 500Ω, while the resistance in darkness is nearly 60kΩ, quite a large difference!
A transistor is a current-driven device, whcih meand that in order for it to operate correctly, a certain amount of current must be applied. For this project, nearly any general purpose NPN transistor will do. Some will work better than others, depending on the amount of current required to drive the transistor, but if you find an NPN, you should be good to go.
In transistors, there are three pins: the Base, emitter and collector. With an NPN transistor, the base pin must be made more positice than the emitter in order for the transistor to work.
The general idea here is that we want to use the resistance of the photoresistor to adjust how much current is allowed to flow through the LEDs. Because we don't know the exact current required for our Transistor, and because you may be using a different photoresistor than me, the value of your resistor in this step (R4 in the picture below), may be different than mine. This is where experimentation comes in. 16k was just about perfect for me, but your circuit may require a different value.
If you look at the schematic, you'll see that as the resistance value of the photoresistor changes, so too does the current through the base pin.
In dark conditions, the value of resistance is very high, so most of the current coming from V+ on the 555 Timer (V+ is the positive voltage) goes both directly to the base of the transistor, making it operational, and to the LEDs.
In lighter conditions, the lowered value of resistance in the photoresistor allows much of that current to go from V+ on the timer directly to DIS. Because of this, there's not enough current to drive the transistor and the LEDs, so you don't see any blinking lights.
Next we'll see the circuit in action!
Alright, let's do it.
We need a few more components for this step:
- A photoresistor (sometimes also called an optoresistor)
- An NPN transistor (most any will do. I can't even read the label on the one I picked, but I was able to determine it's NPN)
- A resistor
A photoresistor is simply a resistor that changes it's value depending on how much light is applied. In a bighter setting, the resistance will be lower, while in the dark, the resistance will be higher. For the photoresistor I have on hand, the daylight resistance is about 500Ω, while the resistance in darkness is nearly 60kΩ, quite a large difference!
A transistor is a current-driven device, whcih meand that in order for it to operate correctly, a certain amount of current must be applied. For this project, nearly any general purpose NPN transistor will do. Some will work better than others, depending on the amount of current required to drive the transistor, but if you find an NPN, you should be good to go.
In transistors, there are three pins: the Base, emitter and collector. With an NPN transistor, the base pin must be made more positice than the emitter in order for the transistor to work.
The general idea here is that we want to use the resistance of the photoresistor to adjust how much current is allowed to flow through the LEDs. Because we don't know the exact current required for our Transistor, and because you may be using a different photoresistor than me, the value of your resistor in this step (R4 in the picture below), may be different than mine. This is where experimentation comes in. 16k was just about perfect for me, but your circuit may require a different value.
If you look at the schematic, you'll see that as the resistance value of the photoresistor changes, so too does the current through the base pin.
In dark conditions, the value of resistance is very high, so most of the current coming from V+ on the 555 Timer (V+ is the positive voltage) goes both directly to the base of the transistor, making it operational, and to the LEDs.
In lighter conditions, the lowered value of resistance in the photoresistor allows much of that current to go from V+ on the timer directly to DIS. Because of this, there's not enough current to drive the transistor and the LEDs, so you don't see any blinking lights.
Next we'll see the circuit in action!
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