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

Analogue Input / Output Slave

The Analogue I/O Slave provides 7 analogue inputs, 1 digital input 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 analogue inputs are designed to work over two ranges which are selectable in software. These are 0 – 5v and 0 – 2.4v. Whenever a voltage appears on an input within the selected range it can be converted to a number in the range 1 – 1023 by the on board A/D (analogue to digital) convertor. The A/D convertor is a 10bit convertor (hence the range 1-1023) giving a very fine resolution of the measurement of the applied voltage. When the range is set to 2.4v the number 1023 corresponds to 2.4v. This means that the measurement resolution is a very useful 2.3mv. With such accuracy it is important to use care when connecting external devices to ensure the connections are not susceptible to interference. Interference can come from many sources including the devices own power supply which may have voltage ripples around its nominal value. As a general guide try to ensure the ground connection is particularly low impedance and perhaps use screened cable to shield the analogue signal being connected. The source of the analogue signal being measured should also have as low an output impedance as possible ensuring the analogue input does not “load it” during the sample and conversion process. Source impedances of less than 2k ohms are usually okay.

Devices which are typically connected to the analogue inputs are usually in the category of sensors. i.e they are responsible for measuring a characteristic from the “real world” and converting it into a voltage proportional to the measurement. These types of devices would measure such things as temperature, pressure, humidity, noise, light, flow rates, weight etc.. etc… The list is probably endless. However, they all have one thing in common. The voltage they produce is proportional, in some way, to the physical characteristic they are measuring. Even if the relationship is non-linear the voltage can be converted into a number and then that number can easily be scaled or otherwise arithmetically manipulated to give the desired result in the appropriate units. The job of the analogue I/O slave is to make these measured voltages available within the control program so that they can be acted on for whatever purpose that the specific application requires. The on board microcontroller takes care of the details of doing the A/D conversion leaving the programmer the simple task of just requesting a reading from the analogue inputs (see software details).
There is one digital input on the analogue I/O slave which can be connected to a standard digital signal in the range 0 – 5v. Alternatively, with a pull-up resistor (as shown), this can also be used as a switch input.

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 Analogue and Digital Inputs On Screw Terminals(TL5)

Pin	Signal description
1	Analogue Input 1
2	Analogue Input 2
3	Analogue Input 3
4	Digital Input 1
5	Analogue Input 4
6	Analogue Input 5
7	Analogue Input 6
8	Analogue Input 7
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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Control Master Full Manual

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