Medical Engineering & Physics 24 (2002) 237–242 www.elsevier.com/locate/medengphy Technical note A versatile drop foot stimulator for research applications D.T. O’Keeffe a,* , G.M. Lyons a a Biomedical Electronics Laboratory, Department of Electronic and Computer Engineering, University of Limerick, Limerick, Ireland Received 17 August 2001; received in revised form 2 January 2002; accepted 21 January 2002 Abstract Drop Foot Stimulators are used to correct hemiplegic drop foot by synchronising the application of Functional Electrical Stimu- lation (FES) of the Common Peroneal Nerve (CPN) to the swing phase of the gait cycle. A research Drop Foot Stimulator (DFS) has been developed with a very flexible architecture to enable the investigation of a variety of gait-correction strategies. The portable unit has been carefully designed to optimise functionality while keeping its size and power consumption to a minimum. The device has two channels of stimulation, with all parameters of stimulation for each channel independently programmable. Four analogue and four digital sensor input channels are provided with a wide variety of sensor types possible. A microcontroller core is utilised to enable the implementation of different control algorithms. A PC-based user interface enables easy programming of the system configuration.  2002 IPEM. Published by Elsevier Science Ltd. All rights reserved. Keywords: Stimulator; Tibialis anterior; Drop foot; Common peroneal; Gait correction 1. Introduction The use of a portable stimulator to stimulate the com- mon peroneal nerve for real-time correction of drop foot was first proposed by Liberson in 1961 [1]. Liberson’s, strategy used a foot switch located at the heel of the affected foot of a hemiplegic subject to synchronise the application of Functional Electrical Stimulation (FES) to the common peroneal nerve with the swing phase of the gait cycle. The Tibialis anterior is the main foot dorsal flexor and is contracted artificially after heel off, and contraction is terminated at heel strike. Since 1961 [1], a variety of peroneal or drop foot stimulators have been developed [2–7]. A standard FES- based surface drop foot correction system would typi- cally contain control and stimulator electronics, sensors and stimulation electrodes (Fig. 1). Leads carry sensor signals to the control electronics and stimulus current to the stimulation electrodes. The sensor-input signals provide real-time information about the subject’s gait to the control electronics, which determines whether stimu- lation should be applied at that time or not. The stimu- * Corresponding author. Tel.: +353-61-202443; fax: +353-61- 338176. E-mail address: derek.okeeffe@ul.ie (D.T. O’Keeffe). 1350-4533/02/$22.00  2002 IPEM. Published by Elsevier Science Ltd. All rights reserved. PII:S1350-4533(02)00011-5 Fig. 1. Drop foot correction system. lation pulses are generated by the stimulation electronics in the portable system and are transmitted to the stimu- lation electrodes, located on the affected leg for common peroneal stimulation. The requirements for a take-home Drop Foot Stimu- lator (DFS), which the user operates in their own home