Digital I/O Slave Module providing Digital Inputs and High Voltage Switching Outputs up to 1Km from the PC

Digital Input / Output Slave

The Digital I/O Slave provides 8 standard digital inputs and 8 high voltage switching outputs which can each switch up to 50v at 500mA. 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 Digital I/O 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.

Board Numbering: One last task is required before the Digital I/O 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’.

Outputs: The switching outputs are slightly different to the digital inputs in their characteristics. They are “open collector” type. This means that they behave like a switch which is either open or connected to 0v. When an output is set to “On” (logic ‘1’) the switching output is closed. If you need to have a straight forward digital signal from one of these outputs, all that is necessary is to connect a resistor between the output and the positive supply of your connected device. The positive supply can be anywhere between 5v and 50v. The choice of the resistor should reflect the input characteristics of your attached device but a typical choice for a 5v system would be around 4k7.
The benefit of having open collector type outputs is that they can also be used for higher voltage and higher current switching than is typical with digital logic. For example each output on the Digital I/O Slave can switch up to 50v at 500mA. This opens the possibilities of connecting a much wider range of electrical and electronic devices directly to the outputs. These can include DC motors, solenoids, lamps, LED’s, Relays etc… etc…

By virtue of the fact you can directly drive relays from these outputs, it means that devices with much higher power requirements can be driven from the controlled relay.
When connecting devices with an inductive load (eg motors, solenoids, relays) it is advisable to make use of the transient suppression facility provided on the board. This is simply a series of transient suppression diodes built into the main output driver chip which act in a way as to “clamp” any transients to the positive external supply. Transient voltage spikes are a result of switching off inductive devices. The collapsing magnetic field acts in a way so as to generate much higher voltages than is normally present. These spikes can be potentially damaging to any connected components and can also cause interference to nearby RF sensitive devices such as a radio. To make use of the suppression facility, simply connect the transient suppression pin directly to the positive terminal of the external supply.

Pinout of the 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 High Voltage Switching Outputs On Screw Terminals(TL3)

Pin	Signal description
TS	Transient Suppression
1	Switching Output 1
2	Switching Output 2
3	Switching Output 3
4	Switching Output 4
5	Switching Output 5
6	Switching Output 6
7	Switching Output 7
8	Switching Output 8

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