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Fabricate a high-resolution sensor-to-USB interface

23 Nov 2011  | Zoltan Gingl

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The circuit in this Design Idea combines a mixed-signal microcontroller, USB UART (universal asynchronous receiver/transmitter), and novel adaptable analog sensor-input circuit. It allows you to connect many types of sensors to the design's two analog-input channels, control the device, and read measurement data on a USB host. The USB connection powers the circuit. You can control the device from your computer with simple commands; even terminal software can make the measurements. The 8051 core allows for easy programming with freely available tools, such as IDEs (integrated development environments), debuggers, and C compilers.

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The design is based on an $8 microcontroller that features an 8051 architecture as well as a PGA (programmable-gain amplifier) and 24bit sigma-delta ADC (Figures 1, 2, and 3). Microcontroller IC1 has an input multiplexer allowing differential or single-ended mode. It also has two DAC outputs and can provide five unassigned digital-I/O pins (Figure 1). One output pin drives D1 under program control. The remaining digital pins are used to configure the two analog-input ports. You also send the microcontroller's reference output to one of the analog-input ports. Four remaining digital pins interface with the USB's UART chip (Reference 1).

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A 3.3V linear regulator, IC2, powers the microcontroller (Figure 2). You power USB chip IC1 directly from the USB port through a ferrite bead and filter network. This popular and reliable USB UART chip lets you communicate with a computer using any operating system. Op amp IC4 buffers the microcontroller's reference output (Figure 3).

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" A precision analog acquisition system that fits in your pocket.

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