Relay Slave Module providing Digital Inputs and 6Amp Changeover Relay Outputs up to 1Km from the PC

Relay Slave

The Relay Slave has 8 digital inputs and 8 changeover relay outputs. Although both the Analogue I/O Slave and the Digital I/O Slave are capable of directly driving relays connected to their outputs it can be more convenient to provide this level of switching on the one board. This is the function of the Relay Slave. With a Master Controller already connected to the PC this slave module can be up to a massive 1Km away connected only by a single pair of low cost wires.

General: To operate correctly the Relay Slave needs to be supplied with an operating DC voltage of between 6v and 12v. This should be connected to the terminals labelled 6v (+ and -) on TL2. The power supply should be fully regulated and capable of providing at least 100mA. The Board also needs to be connected to a Master Controller using the two wires on TL1 (A and B). Connecting ‘A’ to ‘A’ and ‘B’ to ‘B’. Alternatively it can be connected to any other slave module which is already connected to the Master using the same connection strategy. Use of the SCN connection is optional but where used it should be connected to the metal foil shielding on a twisted pair cable. . In addition to the above supply the Relay Slave needs an additional 12v DC supply to power the relay coils. This should be connected to TL12 as shown. Although it is possible to use the same 12v supply to power both the board circuitry (on TL2) and the relay coils (on TL12) it is not ideal since the switching of the relay coils on and off may cause transient voltages which may interfere with the normal operation of the board.

Board Numbering: One last task is required before the Relay Slave can take part in the main control system and that is to allocate it a board number. It is necessary to allocate each board a unique “Board Number” so that commands and data from the Master Controller can be directed at the correct slave board. This is done by setting the blue DIL switches on the board labelled “Board Number”

Inputs: The 8 digital inputs have characteristics compatible with standard 5v logic devices. i.e. when the input is at +5v it will be read as a logic ‘1’ or “High”. When the input is at 0v or GND it will be read as logic ‘0’ or “Low”. As a convenience for use in control systems, the inputs also have “on board” pull ups. This is simply a 10K resistor connected between each of the inputs and the board +5v supply. This means that any unused inputs can be left disconnected without concern over what voltage they are “floating” to. Since the inputs are very high impedance (cmos type) they would “float” somewhere between 0 and +5v if left unconnected giving inconsistent results when read. Unconnected inputs would therefore be read as a logic ‘1’. The 10K resistor is sufficiently high value so as not to impose a great load on any signal source connected to it and also makes it very easy to use switches on the inputs. i.e. a switch can be connected directly between any input and the 0v (GND) connection to provide a functional digital input. When closed the input would read as logic ‘0’, and when open as logic ‘1’.

Relay Outputs: The 8 Relay outputs are available on 8 sets of 3 way screw terminals labelled simply 1 to 8. The centre terminal in each group of 3 is the changeover connection which is connected to the left hand terminal when the relay is not energised and the right terminal when energised. Left and right are determined when looking at the wire entry face of the terminals. Directly behind each relay is an LED indicator showing (when on) that the relay is energised. The contacts are rated for 6A at up to 250v AC (or 30v DC).

Caution: Although the contacts are rated for high voltages, there is no protection provided for the exposed live terminals particularly on the underside of the board. If this board is to be used with high voltages then care should be taken to ensure all exposed terminals are made safe by using suitable enclosures or other techniques. The board should not be used “as supplied” with high voltages. If in any doubt consult a qualified electrician.

Pinout of the Analogue and Digital Inputs On Screw Terminals(TL5)

Pin	Signal description
1	Digital Input 1
2	Digital Input 2
3	Digital Input 3
4	Digital Input 4
5	Digital Input 5
6	Digital Input 6
7	Digital Input 7
8	Digital Input 8
GND	GND (0v)

Pinout of the Relay Contacts on Terminals 1 - 8
(when viewed from cable entry side of terminals)

Left	Middle	Right
Normally Open (N/O)	Common (Com)	Normally Closed (N/C)

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Control Master Full Manual

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