BT redcare Cost-Reduced Vending Interface Unit (VIU-4)


An early prototype of the BT redcare cost-reduced Vending Interface Unit (VIU-4)

The BT redcare vending telemetry service - vend online - is a comprehensive, web-based machine-to-machine monitoring system that provides vital management information about an operator's vending machines 24 hours a day, every day of the year.

Individual vending machines to be monitored by the system are fitted with a Vending Interface Unit (VIU); this unit retrieves audit data (sales statistics, etc) from the machine and transmits this information via GPRS to the central vend online servers.

The VIU is also able to monitor various other conditions at the machine, including temperatures, door opening/closing, and the state of the machine illumination.

All information is held in non-volatile storage at the VIU until positive confirmation is received from the central server that it has been successfully uploaded. This ensures that no data is lost in the event of GPRS failure, or loss of power to the vending machine.

Following the successful development of the original VIU, BT redcare observed that the majority of installations used only a subset of the VIU's capabilities. Therefore a low-cost VIU was conceived by towards the end of 2003 - supporting only the most commonly required features.

redcare Technology Ltd again approached Antronics Ltd for assistance in the embedded firmware development.

Antronics Ltd were able to assist redcare Technology in a number of specific areas:

Triscend Logic Reduction

One area of cost reduction was the use of a lower-cost member of the Triscend E5 family. After an initial feasibility study to confirm that this was possible, Antronics Ltd undertook the port and successfully implemented all of the required functionality within the smaller programmable logic resources:

    UARTs: The 8032 processor core provides one standard UART, and a further two were implemented in programmable logic. This allows simultaneous communications with the GSM/GPRS modem, DEX, and a "debug" port. An "interrupt expander" - also implemented in programmable logic - allows all three additional UARTs to share a single interrupt input to the 8032 processor core.

    2-digit Multiplexed 7-Segment Display: Multiplexing was implemented in programmable logic to relieve the software of the need to constantly scan and update the display: the software simply writes the required 2 digits to a 4-byte register, and the programmable logic does the rest.

    2-Wire Serial Interface: A real-time clock and EEPROM are attached to a 2-wire (IC-compatible) serial peripheral interface. A SoftModule from the standard Triscend library provides a simple register and interrupt interface to the software, while all timing and data serial/parallel conversions are handled in the programmable logic.

    Memory Interface: The E5 provides a highly configurable memory interface unit; this is programmed for the size, width and speed of the external Flash PROM. Additional address decoding and timing control for an external battery-backed SRAM were implemented in programmable logic.

    Other Peripheral Interfaces: A conventional 8051 microcontroller accesses its IO lines via 8-bit Ports; this can be inconvenient where many interfaces of less than 8 bits are required - since the individual IO lines have to be "packed" and "unpacked" into the 8-bit ports. The E5 removes this problem by allowing IO registers of arbitrary size to be implemented.

E5 Configurable Microcontroller


Over 500 VIU-4 units are now installed and undergoing live field trial with a major UK soft drinks vending operator.


We are grateful to BT redcare for their kind permission to feature their VIU-4 in this article.

Please note that Antronics Ltd does not sell or support BT redcare products or services - for details of BT products and services, please contact BT:

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