The EX1000 is an attachable sensor board that is compatible with all the CMXX00 series of WSN Motes that have the Hirose® 51-pin connector. The EX1000's aim is to extend the motes I/O capability, as it is designed to connect external sensors to CMXX00 communication modules. The sensor board has the following general characteristics:
- ADC 4 ports, GPIO (UserINT) 2 ports
- RS232, 2 ports SP3232 SIPEX®
- VoltAmp, 2 ports LMV932 National Semiconductor®
Many different kinds of sensors can be connected to the EX1000, depending on their type and output signal. It is possible to plug the following signals into this board: digital signals, current (range: 4-20mA) signals and dynamic range analog signals.
|Operational Amplifier||Texas Instruments® LMV932||Amplifies analog signal input|
|RS-232 Transceiver||MAXIM® MAX232||Converts TTL signals to RS232|
|Connectors & Jumpers|
|51-pin connector||Hirose® DF9B-51S-1V||Attachable with CMXX00 series of motes|
|3 pin male header molex||Analog Devices®||Serial port connector included|
|Terminal block||Modtronix® TB12B-F254-R4||12 pin|
Sensor Board Overview
Direct ADC Analog Input Signals
The EX1000 allows direct access to the microcontroller's ADC ports 0 to 3. If needed, it is possible to add a voltage divisor to each port for the sensor's output signal conditioning, ensuring correct V/I operation range. If the sensor output does not need conditioning then there is no need to use the resistors R2, R4, R6 and R8, which are connected to ground (GND), and the same with R1, R3, R5 and R7, which are connected to VCC. In any case, a cable must be connected in place of the resistors for the ports to work.
In order to control the input data range properly, it is recommended to use resistance values between 1kΩ ~ 1MΩ which reduce the error of ADC measurements. For example, if the input voltage is 5V (maximum), even using 2.5V as ADC reference voltage it will be saturated (out of range). However, if the ADC0 is used by setting 10 kΩ resistors in R1 and R2, the ADC0 input voltage would then be between 0~2.5 V applying the voltage distribution law, which is perfectly measurable:
- (Ex_A0 - ADC0)/10kΩ = ADC0/10kΩ
- ADC0 = Ex_A0 / 2
Amplified ADC Input Signals
The EX1000 provides 2 inputs connected to operational amplifiers, AMP0 (connected to ADC4) and AMP1 (connected to ADC5).
These devices gives the possibility to amplify the sensor signal output (if needed), in order to obtain an improved sensor conditioning, before giving it as input to the ADC ports. It is possible to configure the amplifier's total gain by welding different resistors:
- GAINAMP0 = 1 + (R10/R9)
- GAINAMP1 = 1 + (R12/R11)
It is also possible to combine both operational amplifiers together to connect balanced-input sensors.
- 1. In order to control the range of input data properly, only use resistance values between 1kΩ~ 1MΩ, which reduce the error of ADC measurements.
- 2. Note that noise is also amplified while amplifying the original signal.
- 3. If batteries are used as source of power, output voltage error may occur . It can be solved by reducing the used voltage as an amplifier bias input.
4-20 mA Transducer Input Signals
In case of current output sensors, the EX1000 has two inputs that can be configured as 4-20 mA transducers, which are directly connected to ADC6 and ADC7 of the MPS430 integrated ADC. It is recommended to be sure that the current input satisfies the CMxx00 current input range. If the sensor current output is out of range, the voltage output may damage the mote.
Digital sensors can be connected to the available UINT0 and UINT1 inputs. These signals are connected directly to ports P2.0 and P2.1 of the MSP430 microcontroller. A sensor driver could therefore be implemented in the MPS430 for controlling the digital sensor through these two pins. The digital signal range is 0 ̴ 3v.
The pins can also be configured as output signals, being possible to generate a 0 ̴ 3v output signal by adjusting the resistances with a defined value and connecting them to an adequate voltage level.
The EX1000 provides two Molex 51004-0300 connectors that are directly connected to the MSP430 microcontroller's UART ports.
These kind of serial sensors can be controlled by the mote directly , acquiring data and doing the signal treatment in the same way that operates within the integrated or directly connected sensors. It is strongly recommended to be aware of how the sensor's UART works, because if another serial controller exists in the sensor itself then most probably the sensor signals will probably not be understood directly by the mote. This is also the case if the voltage range of the output sensor is different from ±9-12V.