SpaceLogger Hardware Description

• Block Diagram

• Power Supply

• Analogue inputs

• Digital Inputs/Outputs

• Communications Ports

• Expansion Port

• Real Time Clock

• Processor Resources

1    Block Diagram

A functional block diagram of the data logger appears below:

2    Power Supply

The data logger operates from a nominal 9-42 VDC external supply capable of supplying at least 100mA.  Alternatively an external regulated supply of 5V ±5% capable of supplying at least 100mA may be used as a power supply.  The module has a storage capacitor for maintaining the real time clock over shorter periods of time.

The power supply select link must be set appropriately depending whether the external supply is regulated 5V or unregulated 9-42V.  The power supply select link is located on top of the pcb module alongside the CompactFlash header.

3    Analogue Inputs

There are 4 10-Bit analogue inputs which measure input levels between ±5 VDC.  The amplifier used in the analogue input stage is rail to rail input and output; the input is voltage divided prior to amplification so a range of –5V to +5V input voltage is available. If a higher input impedance is required then removing the pull down resisters (R3) is possible.   

Analogue input circuit.

4    Digital Inputs/Outputs

There are 4 general purpose digital lines which may be configured as either inputs or outputs, and may also be logged.  There is a series resistance of 1kW between each external connection and the connection to the SpaceLogger processor.

5    Communications Ports

There are two serial communications ports available, the first is software configurable as RS232 or RS485, whilst the second is suitable for RS232 communications over short distances.  This second port does not conform to full RS232 standards and is aimed to be used as a secondary port for development and debugging operations.

For RS232 connection to the main serial port, connect to RxA, TxA and GND.  RxA and Txa Refer to the SpaceLogger receive and transmit.

For RS485 connection to the main serial port, connect to RxA, RxB, TxA, TxB and GND, again labels refer to the SpaceLogger receive and transmit. 

6    Expansion Port

The expansion port is available for future applications where the SpaceLogger may be connected to a second module.  The connections from the SpaceLogger processor to the expansion interface include the 8-bit data bus, the SPI serial interface and several I/O port lines. The expansion port is a series of 22 connections configured in a 2x11 0.1" grid suitable for connecting a header. Pin 1 of the expansion port is top left when viewed from the compact flash side of the circuit board.

7    Real Time Clock

The real time clock module of the SpaceLogger has a resolution of 1 second and will continue to operate even when the processor has been put into is low power sleep mode.  The real time clock also operates from its own power supply in the form of a memory storage capacitor.  This capacitor will charge when the external supply is connected, taking some minutes to fully charge.  Once the external supply is removed the memory storage capacitor supplies power only to the real time clock in order to maximise the time which the real time is stored.  This is of the order of about 3 days.  Once the memory storage capacitor  charge is depleted the real time clock will cease operation, and on power return to its default reset time and date.

8      Processor Resources

Beyond the basic logging functions of the SpaceLogger, an overview of the processor resources available to those wishing to develop applications of their own are detailed below.  These are in addition to the resources detailed above such as the analogue inputs, digital input/outputs and communication ports.

 
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