Dec 06, 2012
By Mark Hastings
In this part, we ll see how to interface an amplified compensated pressure sensor with PSoC3 and evaluate the system performance. This type of pressure sensor is very expensive as it performs both amplification and temperature compensation. The Honeywell SSCDANN015PGAA5 will be used for interfacing with PSoC3. The important specifications of SSCDANN015PGAA5 are listed below
Important specifications:
Supply Voltage: 5V
Accuracy: +/-0.25%
Total error band: +/-2% FSS
Sensor Operation:
This sensor has an amplified and temperature compensated output and is driven by a voltage supply. The output curve and equation are shown below.
Design:
The design is very simple as both amplification and temperature compensation are done within PSoC. Resolution should be 1/1000th of full scale, hence a 10-bit ADC is required. The sensor output voltage goes to 90% of the supply voltage, so the ADC range should be vssa vdda. The ADC should operate with the rail-rail buffer enabled. Sensor output is ratiometric and the ADC reference should be Vdda/4.
PSoC Top Design and ADC configuration:
List of all errors:
|
S.No
|
Parameter
|
Error at 10 psi (in psi)
|
|
Sensor
|
|
1
|
Total error
|
0.2
|
|
2
|
Non-linearity
|
0.022
|
|
Signal Chain
|
|
5
|
Offset
|
0
|
|
6
|
Gain error
|
0.02
|
|
7
|
Offset drift (at 50°C)
|
0
|
|
8
|
Gain drift (at 50°C)
|
negligible
|
|
9
|
INL
|
negligible
|
PSoC Value:
Although not as many analog resources are required when interfacing a pressure sensor with an amplified output, integrating a sensor with other PSoC features such as capsense, segment LCD drive and communication protocols, etc, will lower overall system costs.
Conclusion:
PSoC3 and PSoC 5LP can sense pressure accurately while reducing BOM cost and board space by integrating the analog front-end, ADC, reference and MCU. PSoC ADC inputs can be multiplexed with many inputs (limited only by the GPIO count) allowing interfacing to multiple pressure sensors or other analog sensors. The PSoC Creator design environment makes it easier for you to design and debug, reducing the design time and your time to market.
By Praveen Sekar