HARDWARE CONSIDERATIONS IN TELEMETRIC MONITORING OF PHYSIOLOGICAL VARIABLES

B.R.Hayes-Gill, J.Taylor, A.Hendroff, J.Ashley, J.A.Crowe, and C.J.Paull
Department of Electrical and Electronic Engineering,
University of Nottingham, University Park, Nottingham, UK, NG7 2RD
Email: brhg@eee.nott.ac.uk

INTRODUCTION The choice of hardware for a wireless application depends upon: data rate; local processing requirements; transmission range; protocol; cost; and size. The design of high frequency RF transmitters is not only a specialist task but necessitates license applications. Hence off the shelf, license exempt, RF units are a more efficient choice in terms of time and expense. This paper discusses the restrictions placed on the choice of hardware for three wireless physiological monitoring applications.

METHODS The first application is to provide a multi-user, leadless, intrapartum monitor utilising a 418MHz transceiver. Simultaneous patient monitoring requires data compression and a reliable protocol. A microcontroller was chosen due to its high processing capability, reprogrammable nature and available C compiler. Data integrity is essential and so the RF units must have transmit and receive for data acknowledgment.

The experiences gained from this project led to the application of telemetry to temperature monitoring of multiple sites on the body during surgery. In this case the data rate is low and minimal processing is required. However, the transducers must be small and hence a custom IC integrating an on-chip, low frequency, short range, license free transmitter is planned which will greatly reduce size and cost. A local receiver unit, positioned within 1.5m, will collect data from all sites and retransmit to a base station via a 418MHz transmitter.

The final application is the monitoring of heart rate, speed, stride length and respiration of free running horses. A central unit on the horse, again controlled by a microcontroller, collects all data. Footfall data is passed to this unit via a 418MHz transmitter attached to the horse’s leg. All data is then transmitted via a 458MHz long range (4km) transceiver to a base station.

RESULTS Block diagrams, power requirements and real time physiological data of all three applications will be presented.

DISCUSSION The choice of hardware for a wireless application depends upon: data rate; local processing; transmission range; protocol; cost; and size. Alternative hardware solutions are presented one of which uses a microcontroller and the other a custom IC.