Patent ID: 7943034

Claim:
An apparatus comprising a circuit for applying a stable voltage to an electrochemical test cell received within the apparatus, said circuit comprising: (a) a first connector for making contact with a working electrode in the electrochemical test cell, (b) a second connector for making contact with a counter electrode in the electrochemical test cell, (c) a working-side circuit connected to the first connector, (d) a counter-side circuit connected to the second connector, and (e) a microcontroller receiving input from the working-side circuit and the counter-side circuit, said microcontroller being programmed to provide output of an amount of analyte in a liquid sample disposed within the electrochemical cell when the electrochemical cell is in contact with the first and second connectors, wherein the working-side circuit comprises a first operational amplifier having the output and inverting input connected to the first connector, a first signal input controllable by the microcontroller, said first signal input being connected to the non-inverting input of the first operational amplifier, a first working-side signaling line connected to the first signal input or a second working-side signaling line connected between the output of the first operational amplifier and the first connector, or both; and the counter-side circuit comprises a voltage reference second, and third operational amplifiers and first and second switches controllable by the microprocessor, a second signal input being connected to the microcontroller via a first counter-side signal line, said second connector being connected to the microprocessor via second operational amplifier and a second counter-side signal line when first switch is closed, said second operational amplifier acting as a current sensing device or current to voltage converter (I/V) with respect to the signal from the second connector, and having second signal input connected to the non-inverting input, said third operational amplifier connecting the second connector to the microcontroller via a third counter-side signal line, and said second switch being disposed in a loop connecting the inverting input and the output of the second operational amplifier, whereby opening or closing the second switch alters the gain of the second operational amplifier.