automatic dimming nightlight - circuit board assembly
Material: jumper printed circuit board IC1: 741 op amp IC2: 741 op amp terminal connector R1: 1 m Ω R2: 5 k Ω variable R3: 2. 2kΩ R4: 3.
3 m ω C1: 2200 f 10 V C2: 2200 f 10 V D1: 1N4001 D2: D3: D4: 3.
5 v LED S1: SPST locking switch S2: instant switch plastic item box T1: 6 V 400 mA DC power supply some glue and heat shrink tube may also be helpful.
Tool: drill soldering iron wire cutting machine pliers screw driver this is the circuit I designed for this project.
To power this project I am using a 6 v 400 mA DC power supply. Its open-
Circuit Voltage (no load)
About 10 V is measured with volt meter.
The load running voltage of this project is about 9. 5V.
The circuit can be divided into two parts: timer circuit and dimming circuit.
The timer is made from a 741 op amp connected as a comparator.
It compares the voltage on the capacitor with the reference voltage set by R2 and r3.
C1 is charged to the supply voltage when S2 is pressed.
C1 then gradually discharges through r1.
As long as the voltage at both ends of C1 is greater than the reference voltage, the output of the op amp is high (about 8. 7V).
Keep C2 charged.
When the voltage at both ends of C1 falls below the reference voltage, the output of the op amp becomes low (about 1. 9V).
This may take 0-
45 minutes depending on how the variable resistor is set.
When this happens, C2 starts to discharge slowly through r4.
This starts the dimming cycle.
The second 741 op amp is wired as a unit gain amplifier.
Output mirror voltage on c2.
When the voltage at both ends of C2 goes down, the output voltage and LEDs also darken.
LEDs take about 45 minutes from full light to full dark.
Pressing the button at any time resets the entire cycle.
The SPST slide switch turns the power on and off.
The duration of the light to be lit at full brightness and the time to darken can be modified by changing the values of R1, C1, R4, and c2.
By changing the ratio of the resistance to the capacitor, you can change the speed at which the capacitor is discharged.
For a reasonable estimate of how the capacitor will discharge, you can use the formula Vc = Vo * e (-t/RC).
Testing your circuit on the breadboard before welding can help solve the error.
Then, if the bread plate prototype works, weld it to the circuit board.
I am using a printed circuit board that is laid out like a breadboard.
So I don't need to change my layout.
I am stacking some parts to save space.
So it's important to make sure there are no shorts.
I used a PC jumper to connect the variable resistor, some of which were trimmed off.
For my light source, I am using three LEDs in series and their combined voltage is close to the supply voltage, so I give up adding resistors.
I tend to use a lot of heat shrink tubes to isolate my welding connections.
I found it helpful to avoid unwanted shorts.
Once you have built the circuit, find the right housing.
Then drill some holes for LEDs, switches, dial and power cord.
Trim your board so it will be as big as it must be.
This will be very helpful when it comes to installing everything in the housing.
Finally, the project is finished by loading all the components.
The last step is to make it look good.
You can add a diffuser or something to disperse the light if you want.
You can color the LEDs gel or just the liquid highlighter.
The final aesthetic detail depends on you.
I put my in the decorative lantern.