CE203972 PSoC® CY8C4Axx Comparator with Programmable Voltage Reference.pdf

CE203972 - PSoC® CY8C4Axx Comparator with
Programmable Voltage Reference
Objective
This code example uses a programmable voltage reference and a single comparator to determine if an input voltage is
between two specified voltages.
Overview
This code example checks for a high and low limit then turns on one of three kit LEDs to indicate if the voltage is too high, too
low, or within the high and low limits.
Requirements
Tool: PSoC Creator 3.3 SP2 or higher
Programming Language: C (GCC 4.9.0) or higher
Associated Parts: PSoC Analog Coprocessor
Related Hardware: CY8CKIT-048
Design
This design uses a single comparator ( Comp_1 ) in conjunction with a programmable voltage reference ( PVref_1 ), to create
a window comparator. A window comparator indicates when a voltage is between two set points. Normally two comparators
would be required, but since the programmable voltage reference is adjustable, only one comparator is required. The firmware
adjusts the voltage reference, checks the comparator output, and then turns on the correct LED to signal if the voltage is
between the set points, above the high set point, or below the low set point.
Figure 1 Project Schematic
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PSoC® CY8C4Axx Comparator with Programmable Voltage Reference
Design Considerations
The reference source for the programmable voltage reference is either based on the 1.2 volt system voltage reference (by
default), or the supply voltage Vdd. The programmable voltage reference (PVref_1) allows the user to select an output that is
between the reference source and Vss in 16 equal steps. When the 1.2 volt reference source is used, the user may select a
value between 75 mV (1.2V/16) to 1.2 volts in steps of 75 mV. Vdd can also be selected as the reference source and the
output will be in increments of Vdd/16. For example, if Vdd = 3.3 volts, the output may be from 206 mV to 3.3 volts in 206 mV
steps.
Hardware Setup
The resistors and LEDs shown in the schematic are mounted on the CY8CKIT-048 kit. The three Off-Chip LEDs are part of a
single RGB (Red, Green, Blue) LED on the development board. A potentiometer connected between Vss and Vdd will need to
be added by the user. Instead of a potentiometer, any voltage source between Vss and Vdd may be used.
Components
Table 1 lists the PSoC Creator Components used in this example, as well as the hardware resources used by each.
Table 1. List of PSoC Creator Components
Component or User Module
Comp_1
Version
Hardware Resources
1.20
½ of a CTB/CTBm
1.0
¼ of the programmable
reference block
Vin (Analog Pin)
2.20
GPIO ( P0[7] )
RedLED
2.20
GPIO ( P1[4] )
GreenLED
2.20
GPIO ( P0[2] )
BlueLED
2.20
GPIO ( P1[6] )
PVref_1
Parameter Settings
Both the programmable voltage reference (PVrev_1) and the comparator (Comp_1) components use their default
configuration for this code example.
Operation
To evaluate this code example perform the following steps:
1)
Attach a potentiometer as shown on the schematic in Figure1 or apply an external voltage source to port P0[7]. Be
careful that the external voltage source stays within the range of the PSoC’s supply of Vss to Vdd.
2)
Slowly adjust the input voltage from 0 volts to above 1.5 volts.
3)
Monitor the LED status with respect to the voltage input.
a.
Blue LED should be on when input voltage is below 0.5 volts.
b.
Green LED should be on when voltage is between 0.5 and 1.0 volts.
c.
Red LED should be on when voltage exceeds 1.0 volt.
The levels at which the different LEDs are on may be adjusted in the source code found in main.c. The “HIGH_LIMIT” and
“LOW_LIMIT” #define statements may be modified to adjust the high and low limits of the window comparator.
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PSoC® CY8C4Axx Comparator with Programmable Voltage Reference
Related Documents
Table 2 lists all relevant application notes, code examples, knowledge base articles, device datasheets, and Component
datasheets.
Table 2. Related Documents
Application Notes
AN211293
Getting Started with PSoC® Analog Coprocessor
PSoC Creator Component Datasheets
Comp
PSoC 4 Voltage Comparator (Comp)
PVref
PSoC 4 Programmable Voltage Reference
Pins
General Purpose IO Pins
Device Documentation
Cy8C4Axx Datasheet
PSoC® Analog Coprocessor: CY8C4Axx Family Datasheet
Development Kit (DVK) Documentation
CY8CKIT-048 PSoC® Analog Coprocessor Pioneer Kit
PSoC® Family Web Page
PSoC® Analog Coprocessor
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Document No. 002-03972 Rev.**
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PSoC® CY8C4Axx Comparator with Programmable Voltage Reference
Document History
Document Title: CE203972 - PSoC® CY8C4Axx Comparator with Programmable Voltage Reference
Document Number: 002-03972
Revision
ECN
**
5101225
www.cypress.com
Orig. of
Change
MEH
Submission
Date
1/22/2016
Description of Change
New Code Example
Document No. 002-03972 Rev.**
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PSoC® CY8C4Axx Comparator with Programmable Voltage Reference
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