![]() ![]() Turning up slightly the timing control will turn the lights on for a few minutes before turning off again. The timer is activated as soon as the timing control is turned above 0V (zero volts). Adjust the 10K potentiometer to control how long the light stays on after dark. However, if you want the light to come on at dark, stay on for a while, then turn off before sunrise. And when the control is set to minimum, the relay turns on the light then off as soon as light returns (sunset to sunrise). The relay will turn on the light when the photoresistor is dark (covered). The CodeĪfter everything is connected according to the wiring diagram above, upload this code to your Arduino: const int photoResistor = A0 Īfter uploading and compiling the code, set the 10K potentiometer to the minimum. Since the relay can draw as much as 80 mA when energized, you could damage the Arduino if you drive the relay directly from it. Note: The relay has a built-in transistor to drive the relay coil as well as a diode across the winding to protect the transistor. Keep in mind that two identical photoresistors may have different resistance ranges. You can check the resistance of the photoresistor in low and high light levels with an ohm meter. The typical range of a photoresistor runs from about 3K ohms in high light levels to many Mega ohms in low light levels. As the light gets dimmer, the resistance increases. In bright light, a photoresistor has a lower resistance. ![]() Photoresistors or Light Dependent Resistors (LDR) are light sensing devices. To prevent back EMF, a diode needs to be placed in parallel with the coil. This induces a large reverse current in the coil, which can damage other components in the circuit. Back EMF happens when the electromagnetic field surrounding the coil collapses back into the coil. When working with inductive loads like relays, solenoids, motors, or stepper motors, it’s important to protect your circuit against back EMF. When the switch is closed, current flows through the coil and the electromagnetic field produced from the coil causes the high voltage terminal to switch to the normally open position: With no current flowing through the coil, the relay is in the normally closed position: Inside the relay is an electromagnetic coil that actuates a high voltage switch when there is current flowing through the circuit. They can be configured to switch AC line current to loads like fans, motors, and lights. ![]() To power the relay, we will use jumper wires to solder the VCC and ground connections to the provided pads on the ATtiny Device PCB.įinally, we can connect the middle pin on the header with one of the Arduino pins and our ATtiny Device will be ready to get programmed and receive its brains.Relays are often used in home automation projects. If you want to know more about relays, I have a dedicated video that you can check. I'll be using the low input signal as per the installed jumper, but since we will connect the relay to a pin header, we need to replace that jumper with a solder bridge on the header. This specific relay module can be controlled both with high and low signals. Since the pin headers on the relay stick up, I'll solder the female header upside down so we can then directly plug the relay into it. Since the Attiny85 needs to be programmed, it is necessary that we are able to remove it from the board and the IC socket gives us the perfect option for that.Īfter the socket, we need to solder the pin headers from where we will connect the I2C control and power on one side, and the relay module on the other. We can start by first soldering the IC socket after we have aligned its notch with the notch on the silkscreen. Additionally, you will need a relay module and a spare Arduino Uno for programming the ATtiny85. Next, you will need an 8 pin IC socket, an Attiny85 microcontroller, a 4 pin male header, and a 6 pin female header. If you choose to buy it, thank you! That money goes into growing this channel where they allow me to make better projects. Option number one is that you build it yourself from a perf board as I did while testing the design.Īnother option is to buy this board from me as I've listed the board for sale on my Tindie shop that I just opened. To start assembling what we first need is this board that I designed and for that, you have two options. ![]()
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