Abstract: A method for detection of passing magnetic articles which includes an initial step of sensing an ambient magnetic field and generating a voltage, Vsig, proportional to the magnetic field. A threshold voltage is generated as a percentage of the peak-to-peak voltage of Vsig. The method further includes the step of generating a proximity detector output voltage that becomes one binary level when Vsig rises to exceed the threshold voltage and another binary level when Vsig falls to below the threshold voltage. The threshold voltage is periodically updated to remain the percentage, within a predetermined tolerance, of the peak-to-peak voltage of Vsig in response to changes that may occur in the peak voltages of Vsig.

Abstract: A bipolar driver circuit includes a primary driver transistor and an independently controlled pre-driver transistor having an emitter connected to the base of the primary driver transistor and a collector connected to the collector of the primary driver transistor. In one embodiment, the collector of the primary driver transistor is connected to the output terminal of the driver circuit for sinking current from a load and, in another embodiment, the emitter of the primary driver transistor is connected to the output terminal of the driver circuit for sourcing current to a load. A first current source is connected to the base of the primary driver transistor and a second current source is connected to the base of the pre-driver transistor. The current sources are commonly controllable by an input signal. Also provided is an inverse conduction prevention circuit for preventing the pre-driver transistor from diverting base current from the primary driver transistor in the sink driver embodiment.

Abstract: A syringe has a needle mounted in the lower end of a tubular mount. A protective cover, in the form of a sleeve, fits over this lower end of the tubular mount, and extends to fully cover the sharp end of the needle. The tubular mount has a pair of elongated, axial slots for the entry and exit of a cog or lug on the inside of the sleeve. Pressure on the sleeve slides the lug up the entry slot and exposes the needle. A cross over slot carries the lug to the exit slot, where it slides down to the lower end of the mount, and over a locking ridge to automatically and securely recover the needle. A spring, coupled between the mount and the sleeve has an axial force urging the sleeve down in either slot, and a rotary force urging the cog towards the exit slot. The lug must be in the entry slot to depress and use the needle, but the lug is then rotated to the exit slot and returned by the spring, automatically, to lock the lug in the safe, covering position of the sleeve.