CodeMachine Wireless ModBus RTUs

The wireless monitoring system consists of a USB connected controller node and optionally up to eight wirelessly connected monitoring nodes. The controller node itself has the same monitoring capabilities as the wireless nodes and so a minimal system may consist of the controller only. The RTUs will work with any ModBus enabled SCADA system, although I will concentrate on Codemachine's own designed SCADA system VID (Virtual Instrument Desktop). Wireless nodes can be used where fixed wiring to an RTU is impractical, or perhaps, high voltage isolation is required, where a floating battery operated device is ideal.

Installation

The FTDI (Future Technology Devices International Ltd.) drivers must be installed on the computer to be connected to the wireless node controller, these can be downloaded from http://www.ftdichip.com/Drivers/VCP.htm where you will also find instructions. Make sure you install the Virtual COM port drivers NOT the Direct Drivers.

Configuration

The controller node presents a ModBus ASCII device on a virtual COM port, working at 38,400 Baud, Even parity, 7 data bits 1 stop bit. The ModBus address is ignored as only one device can be connected per virtual COM port.

ModBus registers

Node Address	Input Registers	Holding registers	Status Bits	Coil Bits
Controller	1..10	1.. 2	1..16	1..16
1	11..20	3.. 4	17..32	17..32
2	21..30	5.. 6	33..48	33..48
3	31..40	7.. 8	49..64	49..64
4	41..50	9..10	65..80	65..80
5	51..60	11..12	81..96	81..96
6	61..70	13..14	97..112	97..112
7	71..80	15..16	113..128	113..128
8	81..90	17..18	129..144	129..144

Each node presents 10 input registers (analogue inputs), 2 Holding registers (analogue outputs), 4 coils (digital outputs) and 7 Status bits (digital inputs) both presented as one 16 bit register justified towards the LSB. Each node has an address 0..8, 0 (Zero) being the controller and 1..8 the wireless nodes. The address is factory configured, and should be specified on order, your first wireless node should be address 1, and subsequent nodes 2,3,4 etc. Without duplication on the same network.

For example: input register 23 would be the third analogue input of the wireless node with address 2.

Input Register Assignments

For each node the Input Registers are assigned as follows

Input Register	Function	Range & Units
1	ADC 1	0..2400 mV
2	ADC 2	0..2400 mV
3	ADC 3	0..2400 mV
4	ADC 4	0..2400 mV
5	Temperature	°C/10 *
6	Supply Voltage	0..4000 mV
7	Spare
8	Spare
9	Spare
10	Spare

* Zero represents absolute zero ie. -273°C and 3730 represents 100°C each increment representing 0.1°C

Prototype hardware

The hardware basically comprises a Jennic 5148 radio module and a few ancillary parts. The photograph shows prototype units (with a debug port wired in and attached to a life support system!) The radio system is based on IEEE 802.15.4 at 2.4Ghz and supports meshed network topologies. The working distance of the wireless node from the controller is over 1Km outdoors, but much less indoors. Routers (based on the same hardware) can be used to extend the range. The Wireless Nodes are battery powered (3*AA cells) which should last for a year, routers are mains powered using an external 5 to 12 Volt supply, the controller node is USB powered.