High Performance, Low Cost…

An Intelligent Environmental Sampling Device (ESD)

The piezoelectric micropump-based system described on this page is a prototype being developed to perform unattended sampling of environmental waters for chemical analysis.

At the heart of the instrumentation is a Propeller P8X32 chip with an FT232R USB-to-serial interface. The sampling device uses a piezoelectric micropump (MP6, Bartels Mikrotechnik) to establish a liquid flow into a separate analyzer stage. The on-board OEM MP6 pump controller is in the 14 pin package just to the left of the centre at the bottom of the PCB. Two PWM waveforms generated by the Propeller chip control the pump flow rate.

Headers at the bottom of the PCB allow connections to an off-board AD7746 capacitance-to-digital converter and to a temperature sensor (TMP37). The former senses the presence of liquid at the inlet to the micropump. When liquid is detected the pump is activated and the pump turn-on time is noted by the on-board DS1307 real-time clock. Pumping action then continues until the C-to-D converter no longer sees available liquid, at which time the pump is turned off.

In order to keep track of the total volume of liquid being pumped the system status is logged periodically (time, pump status (off/on), flow rate and temperature) with the results being stored on the microSD card seen on the left hand edge of the PCB.

An LCD panel displays system information while an on-board, two channel ADC (Microchip MCP3422) measures the TMP37 response and later, will also check battery status in a field version of this instrument.

A low cost nRF24L01+ wireless module (upper centre) provides this instrument with wireless connectivity. This feature will allow a researcher to quickly interrogate the instrument in the field without removing it from deployment.