Communication Box

In general, the external communication unit consists of a complimentary RPC linked to a laptop computer via a serial connection. This RPC is housed in a "communication box", along with additional circuitry for conversion between TTL logic (used in the communication box) and RS232 (used in the laptop computer). The communication box prepared and decoded data to be transferred back and forth between the PACER and the laptop computer.

Since an electronic version of the schematic of the communication box is not available, its major components are described here.

Basically, the communication box contains:

  • A complimentary RPC;
  • 1 PIC microcontroller (PIC16F876);
  • 1 RS232 driver/receiver;
  • A DB-9 connector.
Components are wire-wrapped on a perf board, and kept in a plastic box with dimensions 9cm x 14.5 cm x 3 cm.

RPC:

Although the same model of RPC (RPC-433) is used in the communication box, it is programmed differently than that of the PACER. This RPC controls the data transmission between the PACER and the laptop computer. Unlike that in the PACER which searches for preamble signals every 3 seconds, the RPC in the communication box is configured to listen for preamble signals sent by the PACER continuously.

The PIC source code for programming the RPC of the communication box is provided here: baserpc.asm.

RPC is manufactured by Radiometrix, Ltd.

PIC16F876:

The microcontroller used for the communication box is a 28-pin device operating on an external 8.0 MHz crystal, PIC16F876 manufactured by Microchip Technology Inc. Its main task is to regulate data transfer between the RPC and the RS232 driver/receiver.

The PIC source code for the communication box is provided here: basepic.asm.

RS232 driver/receiver:

For conversion between RS232 standard and TTL logic, a MAX232 manufactured by Maxim Integrated Products, Inc is used.

This semiconductor is especially useful in battery-powered systems, and can operate from single +5V power supply. Zoom

Serial connection:

Showing here is a typical DB-9 male connector. It connects the RS232 driver/receiver of the communication box to the serial port of the laptop computer. Only pin 2, 3 and 5 are connected to the circuit. Zoom

Data acquisition sequence

As an example, here's what happen during a data acquisition event:

  1. User selects programmable features on the graphical user interface (GUI);
  2. The GUI compiles user commands into an ASCII string;
  3. ASCII string is received by the communication box, which converts it to TTL logic;
  4. The RPC of the communication box sends a "wake-up" call to the PACER, to establish continuous data transfer;
  5. The RPC of the PACER receives the "wake-up" call, switches to continuous ON mode, and sends an acknowledgement to the communication box;
  6. The communication box receives the acknowledgement, and sends user commands to the PACER;
  7. The PACER receives user commands and executes them accordingly. Atrial electrograms (AEGs) are collected for a specified period of time and are sent back to the communication box;
  8. The PACER switches back to power-save mode after data acquisition is complete;
  9. The communication box coverts AEGs into an ASCII string, and passes it to the laptop computer;
  10. Finally, the GUI decodes the AEGs, and displays them as waveforms on the computer.

[duke electrophysiology lab website] [duke biomedical engineering website] [duke university website]