Isolated Master Controller


    Control Master uses a Master–Slave principle of operation. In all systems there is one “Master Controller” board which is connected to a computer via a standard USB lead and up to 30 slave boards. The job of the Master is to allow the PC to send and receive data to any of the slave boards. The Master Controller has an "on-board" RS485 driver which provides the necessary signal conditioning to allow communications with slave boards up to a massive 1Km (0.62 Miles) away from the controller. The Master also has an on-board Microcontroller which is dedicated to performing two main functions..
1. Handling the USB interface to the PC
2. Handling the RS485 serial communications to the slave boards.
     There are two different types of Master Controller available. The “Non-isolated Master” is the simplest form offering a direct connection between the PC the Master and the Slave boards. In this configuration all of the boards share the same ground connection as the PC. In many applications this is perfectly acceptable.  For info the Non-Isolated Version click here.  
   However, when there is a requirement to control an “electrically noisy” device which can generate large voltage transients it can be safer to separate this electrically from the PC. The “Isolated Master” achieves this by using high speed opto-isolation components that removes the direct connection between Master and Slave and replace it with an optical signal. This is actually a light emitting diode and a light sensor encapsulated in the same small 8-pin chip. This “light connection” provides isolation for up to 2500 volts. In other words, if there are voltage spikes up to 2500 volts on any of the slaves, they are prevented from reaching the sensitive components of the PC. Installing, connecting and operating the Master Controller is exactly the same whichever version you use
     The “Isolated Master” is only partly powered from the USB port. The Microcontroller and associated components on the Master are powered from USB whilst the RS485 communications components require a separate supply. This should be provided on the terminals marked 6v (+ and -). Although it is labelled as 6v, the external power supply can be anything from 6v minimum up to 12v maximum. The Master has an on-board regulator designed to accommodate this range of input voltages. Whatever supply voltage is used, it should be fully regulated and a good quality DC supply capable of at least 100mA.. .


       The reason that the Isolated Master requires an additional supply for its RS485 chips is to maintain the electrical isolation between the PC and the external circuitry. i.e. if you were to use one of the PC’s power supplies for providing this voltage you would have effectively bypassed the isolation provisions. You should give thought to your overall connection strategy at this point if you are using an Isolated Master. All of your external slave devices should be powered from supplies not linked in any way with the PC to maintain isolation (including the above mentioned power to the Master). It should be noted that there is no reason why the one 6v power supply could not be used to power the isolated master and all of the slaves as long as that power supply was capable of supplying enough current to power all boards attached. Note: There are some advantages is using 4 core cable rather than the single twisted pair which normally links the slaves to the master. The additional two cores could be used to carry the 6v supply to all slaves.
     Once fully powered, the Master simply connects to a slave by connecting two wires. These wires are connected to terminals TL1 and are labelled A and B. Connect the A on the Master to the A on the slave and similarly B to B. This wire can be up to 1Km long and should be twisted wherever possible. The signalling which takes place over this pair of wires is standard RS485 signals which are differential in nature. This means that they are highly immune to electrical noise coming from the surroundings where the cable is routed. Twisting the wires together improves this immunity by making it less likely that an external electrical signal will cause any differential interference voltage in the wires. Connecting to more than one slave is simply a continuation of the two wire connection. This can either be a separate two wires starting at the master and going, perhaps in a different direction, to the second slave or it can be a connection from slave one to slave two. In either case always ensure you connect terminals A to A and B to B. The flexibility in forming a continuous “chain” of slaves connected together and to the Master or to connect them directly to the Master in a “star” configuration allows your wiring to reflect the most suitable routing for your own application.
    Also, remember that each slave can also be connected to other slaves in a star configuration. The only limitation is that no slave can be any more than 1Km from the Master in terms of total length of shortest cable route. This flexibility makes the distributed control system very suitable to a wide variety of installations

       In particularly noisy (electrically) environments, such as heavy industrial applications, it may be advisable to use additional shielding for the pair of wires. In this case you can purchase commonly available screened twisted pair cable which has the two wires plus an overall metal foil screen, which is in turn covered in a plastic outer layer. When using this type of cable the two wires should be connected as normal and the metal foil screen should be connected to the terminal marked “SCN” on the Master and on each slave.    

Compatible with Windows 2000,  XP, Vista and  Windows 7


   To download a copy of the Control Master manual, right click on the link on the right and choose "save target as". This will allow you to download a PDF copy of the manual . 

Control Master Full Manual


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