Project Objectives
High Priority Objectives
The data acquisition device must be completely portable, capable of operating off a battery for 20-30 mins of measurement time.
The device must be able to inject a stable 0 - 2mA, DC current into the thin films while also monitoring and recording this injected current.
The acquisition aspect of the device must be capable of measuring 10 Voltages of 12 permutations sequentially at a rate of 10Hz.
Data acquisition must alternate nodal measurements automatically, independently measuring each voltage node once for a cycle of measurements.
Nodal ADC measurements must allow a 5V range within a 16 bit accuracy.
Data acquisition will be stored locally on the device until retrieval.
Second Priority Objectives
The device ideally will have a form factor similar to that of a phone in X and Y dimensions, but potentially larger in the Z direction.
The device should be robust against general field handling (dropping, transport, etc.).
The device can have a higher sampling rate, for greater time response granularity.
The device can be capable of greater than 12 measurement nodes.
Other Constraints and Issues
Other constraints on the device include: power limiting circuitry, capable of preventing damage to the equipment in the event of a user error, the ability to use a simple AC/DC power supply to charge the device along with battery regulation circuitry necessary for maintaining the integrity of the battery, easy nodal connection hot swapping via a simple external connection (ribbon cable, etc.), and no disassembly required to upload data.
WOW Design Solution
The ideal design for this project is an incredibly robust and accurate data acquisition device. This device would be capable of easy transport and charge on the go, capable of storing vast amounts of data, and capable of probing multiple film skins simultaneously. With a simple, easy to use interconnect between the device and the nodes, the DAQ will probe 16 nodes at a high sampling frequency within a 16 bit accuracy. Nodes can be easily and consciously probed, with feedback given by the system on current readings, battery life remaining, and other metrics of performance relevant to the user. The device should be fairly low cost, allowing for a larger scale deployment if desired. Controlling of the sensor measurements would also be variable, subject to the user's input and desire.
Risk Reduction Strategy
Initial team discussions concerning development of the war fighter portable sensing node have focused primarily on the development of a portable current supply and data acquisition device. This is a major concern and an area of substantial risk for the project since both components are instrumental in providing proper function of the sensing skins. Kenneth Loh and his group have successfully performed real-time data acquisition on the sensing skins using bench-top power supplies and a PC. While this provides a great starting platform, moving to a portable system that is reliable and compact is going to be difficult. In order to mitigate risk and ensure the project moves forward in a timely manner the following risk reduction objectives will be carried out during the last three weeks of this quarter:
To determine full design constraints
We need to figure out acceptable current tolerances for the current injection source.
We need to discuss acceptable operation time and tolerances for device
To develop a reliable battery operated current source
Capable of reliably providing up to 2mA of DC current for 10s intervals
Building a breadboard prototype of this current source circuit
Battery monitoring and charging will be figured out later (lower risk)
To develop and validate multiplexer circuitry given stable current source and voltage measurements
Intermediate Milestones
Weeks 8-10 of Winter Quarter
Decide on a platform for data acquisition
How many channels are required for the ADC to effectively sample at least 12 discrete nodes within the given sampling frequency requirements.
Decide on the micro-controller platform to use.
Decide on the battery technology to power the DAQ.
Decide if we are going to do DAQ switching between nodes internally on the micro-controller board or externally with a switching circuit.
Decide on a method/circuit to use for the required constant current injection
Decide on a power source (battery directly or DAC) to power the current injection within the desired operating tolerance.