Type 2 of ANSARI's Controlling Unit with focus on Sensor Interfacing

» Posted on 9. Jan 2013

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ACU2 – Controlling Unit

 ACU2 PCB Assembly



ANSARI’s Controlling Unit – Type 2 (ACU2) is designed to be an interface for various sensor types. It is capable of storing sensor data locally using an onboard serial Flash with 4 MByte of capacity. Together with each record, the ACU2 can also store a time stamp and the temperature of the sensor at recording time.

The form factor of ACU2 is kept so small, that it can be integrated together with the sensor itself into a very small housing. The PCB is optimized to be fitted into M12 screw housing usual in the industry.

ACU2 can output sensor data and temperature data in analog and digital form on its interface. The digital interface of ACU2 is based on RS232 technology and can transmit the serial data about 15 meters on a cable. The baud rate is user selectable and up to 115200 baud.

A number of ACU2 modules can be networked together using one cable. It can be connected in parallel or cascade mode to build a chain. Each module in the chain becomes its own address (automatically or manually). Individual communication with each module is based on module address in the chain.

Digital processing and interfacing of the module is based on a 16-bit RISC processor with 16 MIPS, 128kByte Flash and 10kByte SRAM. The ADC module is a 200ksps fast 12-bit SAR analog-to-digital convertor with reference generator for sensor biasing if needed.

The chained system can also operate without a host or gateway. The modules are intelligent enough to be grouped and communicate with each other without the need of a master or host module. Configuration and data exchange with ACU2 can be done directly over a RS232 serial port on PC using a hyper terminal application.






  • 16-bit mixed signal RISC microcontroller with 16 MIPS
  • 128kByte code Flash, 10Kbyte SRAM and additional 4MByte external serial Flash
  • 12-bit 200ksps Analog-to-Digital converter with Reference voltage and auto scan
  • Basic timers with real-time clock feature and time stamp for logging purposes
  • SPI controlled programmable gain amplifier with input multiplexer
  • Analog sensor and temperature voltage output with 200mA driving capability
  • Local long term logging capability for 500.000 records with time & temperature stamps
  Sensor Input Interface
  • Low Noise: 12nV/Hz
  • Offset: 25µV, 100µV (max)
  • Zerø Drift: 0.35µV/°C, 1.2µV/°C (max)
  • Two Channel MUX
  • Gain Error: 0.3% max
  • Gain Switching Time: 200ns
  • Input Offset Current: ±5nA max (+25°C)
  • Binary Gains: 1, 2, 4, 8, 16, 32, 64, 128
  • Gain Bandwidth: 350kHz @ G=128 to 10MHz @ G=1
  • Calibration channels @ 10% and 90%
  • Configurable signal reference voltage
  • Operating temperature range -40°C to 125°C
   Digital Interface
  • RS-232 transceiver with three-driver and five-receivers
  • Specified for data rates up to 1000-kbps
  • Enhanced ESD interface Protection:
    • ±8 kV IEC 61000-4-2 Air-Gap Discharge
    • ±8 kV IEC 61000-4-2 Contact Discharge
    • ±15 kV Human-Body Model



Industrial sensors in M12 housing like: IR or light detectors, CO2 Sensors, Motion detector, Humidity Sensor, Smoke detectors, Temperature Sensor, etc


As shown in the picture above the ACU2 module and the sensor together can be easily fitted into small housings like in the industry usual M12 screw housing to build robust small sensor modules. ANSARI’s Programmable Digital Sensors are built on this principal.

ACU2 wiring example

An interesting aspect is how to wire the sensors to each other to create a networked system with same or different sensor types in the chain. Beside other alternative wiring shames, one possible shame is the cascaded wiring of the sensors shown in the figure below.


In this topology the modules are able to number themselves automatically. Each module has its own address to distinguish communication between the modules. If modules are added or removed, the chain is able to detect the change automatically and initiates a re-addressing of the modules in the chain.

This chain can operate without the need of a host system. Any module in the chain is able to communicate with another individual module if desired. The number of sensors in the chain is not limited, but it is recommended to not exceed 256 sensors in a chain.

The both ends of the chain may be connected to each other as shown doted to realize a ring topology. Data shifted to the ring may be verified by sender if an application requires double checking of transferred data through the chain.

Local long term logging capability

The ACU2 is able to log sensor data together with a time and temperature stamp per record. More than 500.000 records can be stored in ACU2. If each minute one record is stored, the ACU2 can store more than one year of data locally!



All dimensions are in millimeters.


Printed Circuit Board (PCB) design

The PCB is routed on 6 layers with chem. gold surface and 18µm thick Cu for each layer.
The PCB is built using FR4 material. The PCB thickness is about 1mm. 
Minimum Cu-Cu gap size is 0.1mm, smallest track size on the layers is 0.1mm and minimum drill size is also 0.1mm. A number of 121 drills are used on the board and all via’s are plugged.





Electrical Interface



Pin# Pin-Name Type Descriptions
1 +5V Power Main Supply voltage
2 SensorTemp Analog Out Firmware controlled output voltage
Digital to Analog converter with 256 steps
with Vref+ selectable by software (1.5V, 2.0V or 2.5V)
3 GND Power Ground
4 Reset RS232-In Software controlled (enable /disable) µController-Rest pin
TxD0 RS232-Out UART0 serial data output 
BSLprg RS232-In Trigger signal for entering BSL mode programming of the µController in conjunction with Reset pin #4
RxD0 RS232-In UART0 serial data input
RxD1 RS232-In UART1 serial data input
SensorOut Analog Out Analog Sensor Conditioned output voltage
10  TxD1 RS232-Out UART1 serial data output

JTAG ping in programming and Debugging mode
General purpose digital I/O pin as alternative function

12  TDI GPIO JTAG ping in programming and Debugging mode
General purpose digital I/O pin as alternative function
13  TMS GPIO JTAG ping in programming and Debugging mode
General purpose digital I/O pin as alternative function
14  TCK GPIO JTAG ping in programming and Debugging mode
General purpose digital I/O pin as alternative function
15  RST Output Reset signal to connected peripherals 
16  Sensor In+ Analog-In Positive analog sensor input signal
17  Sensor In- Analog-In Negative analog sensor input signal

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