Automation studio tutorial pdf
The shield powers the Arduino board. Modifications for Driving a 5V automation studio tutorial pdf module from a 3.
Low Triggered Relays for Use with 3. Step 1: Relay Selection Based on What You Want to Switch on and Off. This is relative straight forward so we will consider it first. Solid State switches for switch mains powered devices. Power Relays Most relay modules sold to connect to Arduino are power relays and are rated for either 110V or 240V. The ratings are usually printed on the relay case. Notice that the maximum DC voltage that can handled is much less then the AC rating.
This is the type of relay you will need to use of switch mains powered devices. These relays will handle most devices used in homes except the highest powered ones like room heaters, stoves, motors. Any wiring to the mains power should only be done by a qualified electrician. A final point, the power relays commonly use silver alloy contacts and are not suitable for switching very low currents like switching Arduino digital inputs. Normally, a switch’s wetting current rating is far below its maximum current rating, and well below its normal operating current load in a properly designed system.
FET switches do not have this problem and can be used to switch very low currents. 100mA to operate the relay coil. Arduino digital output which is used to control the relay switching. Direct Driven Reed Relays5V Reed Relays can be driven directly from the Arduino digital output provided their coil current is less than 20mA. Alternatively if the Arduino board is powered via 12V to its power plug, limit the number of 10mA reed relays to less than 6 as the on board 12V to 5V regulator limits the maximum current that can be drawn from the 5V supply to about 70mA or so. The 33 ohm resistor protects the D7 output from excessive current and allows the diode to do the clamping.
When a digital output is turned off it does not go open circuit, rather it connect the output pin to GND via a very low resistance. Without the additional 33 ohm resistance, the current spike from the coil would preferentially go back into the microprocessor via D7 to GND. TRR-1A 5V reed relay is 3. 75V which means any voltage higher that than must close the contacts so 4. 7V is more then enough to ensure the relay operates. All commercial relay modules should already have the clamping diode fitted across the relay coil.
There are a number of different single 5V relay modules available on-line. But most do not have any circuit diagrams available. The jumper is connecting these two grounds together so you can use it just like the left hand board. Removing the jumper lets you have isolated supplies, one for the the Arduino and another completely separate one for the relays. Separate supplies provides some extra protection against mains volts getting back into the microprocessor. But this extra protection is mostly illusory. The pcb tracks on the back of the board are quiet close and nothing will protect you against a lightning strike on the power line outside your house.
So for either board, connect the relay GND to one of Arduino’s GND pins and the relay 5V or Arduino’s 5V pin and the relay IN to one of Arduino digital outputs, say D4. Then when the digital output, D4, is High the relay will operate. The photo above shows this wiring. Note the Arduino is being powered by the 5V USB power. The relay is 5V so everything is at the same voltage. When the relay is un-powered the NC terminal is connected to the COM terminal and the NO terminal is not connected.
When the relay is operated, the COM terminal switches over and is now connected to the NO terminal and NC terminal is not connected. The screw terminals are either marked NO, NC and COM or small drawing is shown like the image above. Added to this is the current required by the IN input to trigger the coil. For the optically isolated relay that is about 4mA and perhaps a bit more for the non-isolated one.
In any case each of these relay modules will take 4 channel relay shield from Seeed Studio does. This shield is quoted as drawing 250mA, but 300mA would be more realistic based on the datasheet for the relays. In any case it is fine if you are powering the Arduino board via a USB supply. However it is not suitable if you are using a 9V or 12V supply due to the limitations of Arduino’s on-board regulator. An example of this type of relay shield is the DFROBOT Relay Shield for Arduino V2. This shield can be configured in a number of ways using the jumper strips. When operating all 4 relays it should be powered by 9V applied to the screw terminal on the left of the picture.