A medical device configured to conduct a safety check, the medical device comprising: a first electrical lead, including a first tip connection and a first ring connection; a second electrical lead, including a second tip connection and second ring connection; a voltage supply connection; a field programmable gate array; a microprocessor electrically connected to the field programmable gate array; a first current source; a first grounding connection; and a first H-bridge circuit comprising first, second, third, and fourth electrical switches, the first and second electrical switches connected in series to form a first pair, and, the third and fourth electrical switches connected in series to form a second pair, the first and second pairs connected in parallel with each other between the first voltage supply connection and the first grounding connection, and electrically connected to the field programmable gate array, the voltage supply connection, the first current source, and the first electrical lead; wherein the first tip connection is electrically connected between the first pair of series electrical switches of the first H-abridge circuit; the first ring connection is electrically connected between the second pairs of series electrical switches of the first H-bridge circuit; and a first sensing resistor electrically connected to the first current source and the first grounding connection; a digital to analog convertor electrically connected to the microprocessor and the first current source; an analog to digital convertor electrically connected to first sensing resistor and the microprocessor; characterised in that the microprocessor is configured to periodically perform a sequence of tests on the first H-bridge circuit during operation of the medical device, but not while therapy is being delivered, to ensure proper operation of the device; wherein during the sequence of tests at least one of the microprocessor and the FPGA is configured to: activate the first and second electrical switches, and deactivate at least the third and fourth electrical switches; activate the third and fourth electrical switches and deactivate at least the first and second electrical switches; activate the first and third electrical switches and deactivate at least the second and fourth electrical switches; and activate the second and fourth electrical switches and deactivate at least the first and third electrical switches; and if an abnormality is indicated the microprocessor or FPGA aborts use of the medical device. a first electrical lead, including a first tip connection and a first ring connection; a second electrical lead, including a second tip connection and second ring connection; a voltage supply connection; a field programmable gate array; a microprocessor electrically connected to the field programmable gate array; a first current source; a first grounding connection; and a first H-bridge circuit comprising first, second, third, and fourth electrical switches, the first and second electrical switches connected in series to form a first pair, and, the third and fourth electrical switches connected in series to form a second pair, the first and second pairs connected in parallel with each other between the first voltage supply connection and the first grounding connection, and electrically connected to the field programmable gate array, the voltage supply connection, the first current source, and the first electrical lead; wherein the first tip connection is electrically connected between the first pair of series electrical switches of the first H-abridge circuit; the first ring connection is electrically connected between the second pairs of series electrical switches of the first H-bridge circuit; and a first sensing resistor electrically connected to the first current source and the first grounding connection; a digital to analog convertor electrically connected to the microprocessor and the first current source; an analog to digital convertor electrically connected to first sensing resistor and the microprocessor; characterised in that the microprocessor is configured to periodically perform a sequence of tests on the first H-bridge circuit during operation of the medical device, but not while therapy is being delivered, to ensure proper operation of the device; activate the first and second electrical switches, and deactivate at least the third and fourth electrical switches; activate the third and fourth electrical switches and deactivate at least the first and second electrical switches; activate the first and third electrical switches and deactivate at least the second and fourth electrical switches; and activate the second and fourth electrical switches and deactivate at least the first and third electrical switches; and if an abnormality is indicated the microprocessor or FPGA aborts use of the medical device.