Let’s start with the basics. When building a simple controller using an Acorn board, we deal with two types of electricity, AC and DC. AC is alternating current. It is the power that we get from a wall outlet. In North America, it is 120 VAC. In other parts of the world it is 220, 230, or 240 VAC. Common examples of AC power are light bulbs and 1-phase motors. DC is direct current. Direct means that it flows in one direction. Using conventional notation, we say that direct current flows from its positive side to its negative side. Common examples of DC power are flashlights.
Voltage is the pressure that forces electricity along its path. The higher the number, the greater the pressure. The lower the number, the lesser the pressure. A 24VDC circuit has more pressure than a 5VDC circuit.
Current is the amount of electricity flowing through the circuit. Motors can handle the flow many amps. Indicator lights and opto-couplers can only handle the flow of a few thousandths of an amp.
Think of electricity as water in a hose. Voltage compares to the water pressure. Current compares to how much water is flowing through the hose.
Those basic concepts must be properly understood before going on.
The next concept is Sinking and Sourcing circuits. We’re not going to bother with Sinking circuits right now. We won’t be using a Sinking circuit when using the Acorn’s relay board. A Sourcing circuit “sources” or provides current from the plus side of a DC power supply. That current flows from the source, through the device that needs power, and then to the negative side of a DC power supply. Compare it to water running downhill.
Next, we must understand what an electrical circuit is. In our case, it is the full path that electricity follows from the plus side of a DC power supply, through the device being powered, and then on to the minus side of the power supply. The circuit that we’re going to build starts at the +24VDC side of the power supply, goes through the coil of a solenoid (or the LED indicator lamp that I’ll be using to test the circuit), to the minus or negative side of the power supply. Note that some power supplies might be marked +24V and -24V. That does NOT mean that it is a 48V power supply. It means that the + and the – sides of the power supply are marked with the total voltage of the power supply. Sometimes, particularly when the power supply produces several voltages, the minus or negative is marked COM or COMMON. That’s because it is the common reference point for all voltages produced by that power supply.
The relay is next. A relay is just a simple switch with an electromechanical toggle instead of a manual toggle. A relay has two major components, a coil (electromechanical switch) and a set of contacts. The coil and the contacts are separate. The voltage that controls the coil is not the same voltage used by the contacts unless you wire it that way yourself. A relay is labeled by the number of “poles” that it has. A pole is just another word for “separate circuit”. It is also labeled by the number of “throws” it has. The relay board supplied with the Acorn has eight individual SPDT (single-pole, double-throw) sets of contacts. Each set of contacts is controlled by its own coil.
The relay’s coil is configured by Centroidcnc to be controlled by the Acorn board. All we have to know is which instructions to use to turn it On and Off.
We need to know more about relay contacts before we can use the relay board. The relays have three terminals, N/C, Common, and N/O. N/C (normally closed) means that the N/C terminal is in contact with the Common terminal when the relay’s coil is NOT activated. N/O (normally open) means that the N/O terminal is NOT in contact with the Common terminal when the relay’s coil is NOT activated. When the coil is activated by the Acorn, the N/C contact opens and is no longer in contact with the Common terminal. The N/O contact closed and is in contact with the Common terminal. Both the N/C and the N/O contacts can be used, if needed. For example, the N/C terminal could source current to a Red LED indicator lamp. When the relay is OFF, current would flow from the power supply to the relay’s Common terminal, to the N/C terminal, and then to the plus side of the LED indicator lamp. That would provide a source of current for the Red LED indicator lamp. The minus side of the LED indicator lamp would be connected to the power supply minus. That would provide a complete path from the power supply’s positive voltage to the minus, negative, or voltage common on the power supply. By wiring things that way, the Red LED indicator lamp would be ON when the relay’s coil was inactive. If a Green LED indicator lamp were used to show when the relay was active, it would be connected to the relay’s N/O terminal. Current would be sourced to the Red LED indicator lamp via the relay’s Common terminal when the relay’s coil was active.
That’s the mechanical side of connecting something to a relay. We’re not finished yet. We still have to use the Wizard to assign that relay to something. Because the VCP has a button to turn Flood Coolant On/Off, we could assign Flood Coolant to output #2. Then, after saving the configuration, powering down the software and the Acorn and restarting the Acorn, if we turned on manual mode on the VCP and then toggled On the Flood button, output #2 would turn on. If we toggled the Flood button again, output #2 would turn off. We can also control the outputs using G-code. Look at the list of M codes to see which ones to use. If the outputs have not been assigned to another purpose, then codes M61 through M68 turn on outputs 1 through 8 and codes M81 through M88 turn off outputs 1 through 8. Because we assigned Flood Coolant to output #2, we would use code M8 to turn on the Flood Coolant output and code M9 to turn off the Flood Coolant output.
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Use Wizard to assign an Output to a VCP device
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The DC device is a simple LED indicator Lamp. It could have been a solenoid, a contactor, or other DC device.
Connect power supply GND to (-) side of DC device (Black wire)
Connect power supply +24VDC to Relay Common terminal (Yellow Wire)
Connect Relay N/O terminal to (+) side of DC device (Blue Wire)
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For this test, click on VCP Flood Coolant to turn on LED indicator