AN87391
PSoC® 4 Segment LCD Direct Drive
Author: Nidhin MS and Rahul Raj Sharma
Associated Project: Yes
Associated Part Family: CY8C41xxx and CY8C42xxx
Software Version: PSoC Creator™ 3.3 SP1 or later
Related Application Notes: AN52927, AN56384
®
AN87391 demonstrates how easy it is to drive segment LCD glass using the integrated LCD driver in PSoC 4. PSoC 4
offers multiple LCD drive modes, very low power consumption, and provides a complete user interface and system
solution. Using example projects, this application note explains low-power LCD design and a user interface solution that
®
includes CapSense .
Contents
1
2
3
4
5
6
1
Introduction ...............................................................1
PSoC Resources ......................................................2
2.1
PSoC Creator ..................................................2
2.2
Code Examples ...............................................3
2.3
PSoC Creator Help ..........................................4
2.4
Technical Support ............................................4
Features of Segment LCD Drive in PSoC 4 .............5
Basics of Segment LCD ...........................................5
PSoC Creator Component: Segment LCD ...............7
PSoC 4 Segment LCD Direct Drive ..........................7
6.1
PWM Drive Mode .............................................7
6.2
Digital Correlation Drive Mode ......................... 8
6.3
Low-Power Operation ...................................... 9
7
PSoC 4 User Interface Solution.............................. 11
8
PSoC Creator Projects ........................................... 13
8.1
Project 1: Simple Segment LCD .................... 13
8.2
Project 2: Low-Power Segment LCD ............. 20
8.3
Project 3: Segment LCD and CapSense
User Interface ................................................ 23
8.4
Project 4: Alphanumeric Segment LCD ......... 25
9
Summary ................................................................ 26
Worldwide Sales and Design Support ............................. 28
Introduction
Most low-power portable handheld devices such as glucose meters, multimeters, and blood pressure monitors use a
segment LCD to display information. Segment LCDs require an external driver to interface with a microcontroller.
PSoC 4 implements an integrated low-power LCD driver that can directly drive segment LCD glass.
PSoC 4 is a true programmable embedded system-on-chip integrating configurable analog and digital peripheral
®
®
functions, capacitive touch sensing, memory, and a 32-bit ARM Cortex -M0 microcontroller on a single chip. PSoC 4
accelerates time-to-market, integrates critical system functions, and reduces overall system cost. The capacitive
touch sensing capability of PSoC 4 (CapSense), together with LCD drive allows you to implement an entire user
interface solution using only PSoC 4.
PSoC 4 has flexible low-power modes to reduce overall power consumption. For example, the segment LCD current
consumption is as low as 3.1 µA when the PSoC is in its Deep-Sleep low-power mode.
The PSoC Creator™ IDE provides a Segment LCD Component that makes it easy to use different types of segment
LCD modules with PSoC 4.
This application note explains the features offered by PSoC 4’s segment LCD drive, shows best practices for lowpower LCD design, and demonstrates user interface solutions with the help of example projects.
®
If you are new to PSoC 4, refer to AN79953, Getting Started with PSoC 4. If you are new to PSoC Creator, see the
PSoC Creator home page. If you are new to PSoC 4 power modes, refer to AN86233, PSoC 4 Low-Power Modes
and Power Reduction Techniques.
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PSoC® 4 Segment LCD Direct Drive
2
PSoC Resources
Cypress provides a wealth of data at www.cypress.com to help you to select the right PSoC device for your design,
and to help you to quickly and effectively integrate the device into your design. For a comprehensive list of resources,
see KBA86521, How to Design with PSoC 3, PSoC 4, and PSoC 5LP. Here is an abbreviated list for PSoC 4:
2.1
Overview: PSoC Portfolio, PSoC Roadmap
Product Selectors: PSoC 1, PSoC 3,
PSoC 4, or PSoC 5LP. In addition, PSoC
Creator includes a device selection tool.
Technical Reference Manuals (TRM) provide
detailed descriptions of the architecture and registers
in each PSoC 4 device family.
Development Kits:
Datasheets describe and provide electrical
specifications for the PSoC 4 device families
CapSense Design Guide: Learn how to
design capacitive touch-sensing applications
with the PSoC 4 family of devices.
Application Notes and Code Examples
cover a broad range of topics, from basic to
advanced level. Many of the application
notes include code examples. PSoC Creator
provides additional code examples – see
Code Examples.
CY8CKIT-040, CY8CKIT-042, CY8CKIT-044, and
CY8CKIT-046 are PSoC 4 Pioneer Kits are easyto-use and inexpensive development platforms.
These kits include connectors for Arduino™
compatible shields and Digilent® Pmod™
daughter cards.
CY8CKIT-049, and CY8CKIT-043 are very lowcost prototyping platforms for sampling PSoC 4
devices.
CY8CKIT-001 is a common development platform
for all PSoC family devices.
The MiniProg3 device provides an interface for flash
programming and debug.
PSoC Creator
PSoC Creator is a free Windows-based Integrated Design Environment (IDE). It enables concurrent hardware and
firmware design of systems based on PSoC 3, PSoC 4, and PSoC 5LP. See Figure 1 – with PSoC Creator, you can:
1.
2.
Drag and drop Components to build your
3. Configure Components using configuration tools
hardware system design in the main design
4. Explore the library of 100+ Components
workspace
5. Review Component datasheets
Codesign your application firmware with the
PSoC hardware
Figure 1. PSoC Creator Features
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PSoC® 4 Segment LCD Direct Drive
Figure 2. Code Examples in PSoC Creator
2.2
Code Examples
PSoC Creator includes a large number of code example projects.
These projects are available from the PSoC Creator Start Page,
as Figure 2 shows.
Example projects can speed up your design process by starting
you off with a complete design, instead of a blank page. The
example projects also show how PSoC Creator Components can
be used for various applications. Code examples and datasheets
are included, as Figure 3 shows.
In the Find Example Project dialog shown in Figure 3, you have
several options:
Filter for examples based on architecture or device family,
i.e., PSoC 3, PSoC 4 or PSoC 5LP; category; or keyword.
Select from the menu of examples offered based on the
Filter Options.
Review the datasheet
Documentation tab).
Review the code example for the selection. You can copy
and paste code from this window to your project, which can
help speed up code development, or
Create a new project (and a new workspace if needed)
based on the selection. This can speed up your design
process by starting you off with a complete, basic design.
You can then adapt that design to your application.
for
the
selection
(on
the
Figure 3. Code Example Projects, with Sample Code
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PSoC® 4 Segment LCD Direct Drive
2.3
PSoC Creator Help
Visit the PSoC Creator home page to download the latest version of PSoC Creator. Then, launch PSoC Creator and
navigate to the following items:
2.4
Quick Start Guide: Choose Help > Documentation > Quick Start Guide. This guide gives you the basics for
developing PSoC Creator projects.
Simple Component example projects: Choose File > Open > Example projects. These example projects
demonstrate how to configure and use PSoC Creator Components.
Starter designs: Choose File > New > Project > PSoC 4 Starter Designs. These starter designs demonstrate
the unique features of PSoC 4.
System Reference Guide: Choose Help > System Reference > System Reference Guide. This guide lists
and describes the system functions provided by PSoC Creator.
Component datasheets: Right-click a Component and select “Open Datasheet.” Visit the PSoC 4 Component
Datasheets page for a list of all PSoC 4 Component datasheets.
Document Manager: PSoC Creator provides a document manager to help you to easily find and review
document resources. To open the document manager, choose the menu item Help > Document Manager.
Technical Support
If you have any questions, our technical support team is happy to assist you. You can create a support request on the
Cypress Technical Support page.
If you are in the United States, you can talk to our technical support team by calling our toll-free number: +1-800-5414736. Select option 8 at the prompt.
You can also use the following support resources if you need quick assistance.
Self-help
Local Sales Office Locations
www.cypress.com
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PSoC® 4 Segment LCD Direct Drive
3
Features of Segment LCD Drive in PSoC 4
PSoC 4’s segment LCD drive has the following features:
Supports up to 8 common (COM) and 56 segment (SEG) electrodes
Two drive modes: digital correlation and PWM
Programmable PSoC 4 GPIOs provide flexible selection of COM and SEG electrodes.
Supports 14-segment and 16-segment alphanumeric display, 7-segment numeric display, dot matrix, and special
symbols
Operates in PSoC 4’s Active, Sleep, and Deep-Sleep system power modes.
Can drive a 3-volt display from 1.8-volt VDD
Digital contrast control
Note: The number of commons and segments supported by a PSoC 4 device varies based on the device family and
device package. See the respective device datasheets for details.
4
Basics of Segment LCD
A segment LCD panel has liquid crystal material between two sets of electrodes. The top and bottom electrodes of an
individual LCD segment are called the common (COM) and the segment (SEG) electrodes, respectively. These
electrodes form a matrix as Figure 4 shows.
Figure 4. COM and SEG Electrodes
LCD Panel
Resistance
COM3
COM2
COM1
SEG0
SEG1
COM0
The lumped capacitors in Figure 4 represent the capacitive load of the ideal LCD segments. Each pair of COM and
SEG electrodes is connected by only one LCD segment. The root-mean-square (RMS) voltage across a COM-SEG
electrode pair controls the opacity of the LCD segment connected between the electrode pair.
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PSoC® 4 Segment LCD Direct Drive
Liquid crystal materials do not tolerate long-term exposure to DC voltage; therefore, waveforms applied between
COM and SEG electrodes must produce a 0 V DC component on every LCD segment. The drive waveforms also
contain time division multiplexing to simultaneously activate multiple LCD segments. A typical LCD driver generates
AC waveforms with multiple voltage steps on the COM and SEG electrodes. The following terms are used to define
these waveforms:
Duty: A driver is said to operate in 1/M duty when it drives 'M' number of COM electrodes. Each COM electrode
th
nd
rd
th
is effectively driven 1/M of the time. PSoC 4100 and PSoC 4200 devices support 1/2 , 1/3 , and 1/4 duties.
nd
rd
th
th
PSoC 4100M, 4200M, 4100L and4200L devices support 1/2 , 1/3 , 1/4 and 1/8 duties.
Bias: A driver is said to use 1/B bias when its waveforms use voltage steps of (1/B) × VDRV. VDRV is the
nd
highest drive voltage in the system (equal to VDD in PSoC 4). PSoC 4100 and PSoC 4200 devices supports 1/2
rd
nd
rd
and 1/3 biases in PWM drive modes. PSoC 4100M, 4200M, 4100L, and 4200L devices support 1/2 , 1/3 ,
th
th
1/4 ,and 1/5 duties in PWM drive modes. For more information, see Table 1 on page 9.
Frame: A frame is the length of time required to drive all the segments. During a frame, the driver cycles through
the COM electrodes in sequence. All segments receive 0 V DC (but non-zero RMS voltage) when measured over
the entire frame.
th
th
The intensity, or contrast, of a segment LCD pixel depends on the RMS voltage applied across the pixel. Figure 5
shows the relationship between the contrast and the RMS voltage on an LCD segment.
Figure 5. Relationship Between RMS Voltage and Contrast
100%
Contrast (C)
90%
Discrimination Ratio:
D= VHI/VLo
10%
0%
VOFF
VTHR VLO
VHI VON
AC Voltage between COM and SEG (VRMS)
The terms in Figure 5 are defined as follows:
VOFF: The RMS voltage across the pixel below which no contrast change is visible on the LCD
VTHR: The RMS voltage across the pixel at which 10 percent contrast is achieved
VON: The RMS voltage across the pixel at which 90 percent contrast is achieved
VLO: The lowest RMS voltage which the LCD driver can generate
VHI: The highest RMS voltage which the LCD driver can generate
Discrimination Ratio (D): The ratio between VHI and VLO that the driver can realize. A higher discrimination ratio
results in better contrast.
Twisted Nematic (TN) and Super Twisted Nematic (STN) displays are the most commonly available types of segment
LCDs. TN displays require a higher change in RMS voltage to produce a noticeable difference in opacity, compared
to the STN displays. Therefore, for a given discrimination ratio, STN displays provide better contrast than TN
displays. STN displays also have superior viewing angles. However, TN displays are usually cheaper than STN
displays.
For more information on the basics of segment LCD, refer to the PSoC 4 Technical Reference Manual.
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PSoC® 4 Segment LCD Direct Drive
5
PSoC Creator Component: Segment LCD
PSoC Creator provides a Segment LCD Component which allows you to easily interface different types of segment
LCD display modules with PSoC 4. Simply drag and drop the Component onto your PSoC Creator project schematic
and configure it for your LCD module. The Component also provides an easy-to-use application programming
interface (API). For more information, see the PSoC 4 Segment LCD Component datasheet.
Also see the project “Simple Segment LCD”. This project shows you how to interface a 4-digit 7-segment LCD
module with PSoC 4 by using the Segment LCD Component and APIs.
6
PSoC 4 Segment LCD Direct Drive
PSoC 4 supports two segment LCD drive modes, PWM and digital correlation. They use different techniques to
generate the AC waveform required for the LCD glass, and they have different contrast and power consumption
characteristics. The following sections explain in detail the differences between the two drive modes.
6.1
PWM Drive Mode
The PWM drive mode uses high-frequency (32 kHz to 48 MHz) PWM digital signals to generate the low-frequency
(30 to 150 Hz) analog drive waveforms across the LCD segments. The capacitive nature of the LCD segments and
the panel resistance filters the high-frequency PWM signals to generate variable voltage levels across the LCD
segments, as Figure 6 shows.
Figure 6. PWM Drive Mode
GPIO Output Impedance
LCD Panel Resistance
LCD Segment
Capacitance
PWM Generator
COM
V1
V2
PWM Generator
SEG
Voltage at GPIO
(V1)
Vddd
0
t
Effective voltage across a pixel
(V2)
Vddd
2/3 Vddd
1/3 Vddd
0
t
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PSoC® 4 Segment LCD Direct Drive
6.2
Digital Correlation Drive Mode
The digital correlation drive mode is a patent-pending Cypress invention that is ideal for low-power and batteryoperated applications. It works by doubling the drive frequency of the COM signals in their inactive frame intervals.
This changes the VRMS across the segments, which in turn affects the segment’s contrast (Figure 5). Figure 7 shows
an example of digital correlation mode waveforms.
Figure 7. Digital Correlation Example
One ‘Frame’ of LCD drive
(addresses all segments once)
VDD
COM0
0
VDD
COM1
0
VDD
SEG0
0
SEG1
VDD
0
t0
t1
t2
t3
One Frame
COM / SEG is selected
COM / SEG is not selected
Resulting voltage across segments
(VDC = 0)
COM0 -SEG0
VDD
0
-VDD
Segment ON:
VRMS = 0.791 VDD
COM0 -SEG1
VDD
0
-VDD
Segment OFF:
VRMS = 0.612 VDD
VDD
COM1 -SEG0
Segment ON:
VRMS = 0.791 VDD
0
-VDD
VDD
COM1 -SEG1 0
-VDD
Segment OFF:
VRMS = 0.612 VDD
t0
t1
Segment is On
Segment is Off
t2
t3
Discrimination ratio:
D = 0.791/0.612 = 1.291
See the PSoC 4 Technical Reference Manual for an in-depth explanation of each drive mode and its corresponding
waveform.
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PSoC® 4 Segment LCD Direct Drive
The segment LCD glass has the characteristics of an RC series circuit; therefore, its power consumption depends on
the frequency of operation. Because of the very low frequency of operation, the digital correlation drive mode
consumes considerably less current than the PWM drive mode.
However, the contrast and viewing angle of the PWM mode is superior to that of digital correlation mode. This is due
to the PWM mode’s higher discrimination ratio (Figure 5). Table 1 shows a comparison of discrimination ratios.
Table 1. Comparison of Discrimination Ratios
Discrimination Ratio
COM
PWM
PWM
1/4 Bias
1/5 Bias
2.236
1.844
1.612
1.915
1.732
1.567
1.528
1.732
1.648
1.528
1.254
1.414
1.581
1.494
Digital Correlation
PWM 1/2 Bias
PWM 1/3 Bias
2
1.732
2.236
3
1.414
1.732
4
1.291
8
1.134
The actual difference in contrast and viewing angle between these drive modes depends on the characteristics of the
LCD module.
6.3
Low-Power Operation
Follow these steps to reduce power consumption while using PSoC 4 segment LCD drive:
1.
See AN86233, PSoC 4 Low-Power Modes and Power Reduction Techniques and implement the techniques
explained in it to reduce the overall system power consumption.
2.
Enter Deep-Sleep mode whenever possible. Deep-Sleep power mode is PSoC 4’s lowest-power mode that
retains the segment LCD drive capability.
3.
Use the digital correlation drive mode of the segment LCD when the device is in Deep-Sleep mode.
Compared to the PWM drive mode, the digital correlation mode produces reduced but acceptable contrast and
viewing angles on TN displays, and no noticeable difference in contrast or viewing angle on STN displays. However,
the digital correlation mode takes significantly less current than the PWM mode. Table 2 compares the current
consumption of the two drive modes and Table 3 shows the recommended usage of the drive modes.
Note: Table 2 shows the approximate current consumption for a 3 COM, 12 SEG LCD with a PSoC 4200 device. The
actual power consumption depends on the device family, type of LCD used, and the firmware.
Table 2. Typical Device Current Consumption in Deep-Sleep Mode with Segment LCD Enabled
Frame Rate,
Hz
www.cypress.com
Current Consumption, µA
Digital Correlation Mode
PWM Mode
30
3.1
65.9
50
3.8
66.2
70
4.5
66.5
90
5.1
66.7
110
5.8
67.1
130
6.5
67.3
150
7.4
67.6
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PSoC® 4 Segment LCD Direct Drive
Table 3. Recommended Usage of Drive Modes for Low-Power Operation
Display Type
Deep-Sleep Mode
Active and Sleep Modes
Notes
TN LCD
Digital Correlation
PWM
Firmware must dynamically switch between LCD drive modes
STN LCD
Digital Correlation
No contrast advantage for PWM drive with STN LCD
You can change the LCD drive modes on the fly to give the optimum balance between power consumption and
display contrast. Figure 8 shows the firmware flow for dynamically switching LCD drive modes, for good contrast and
viewing angle in the Active mode, and reduced power consumption in the Deep-Sleep mode.
See the “Low-Power Segment LCD” project for more details.
Figure 8. Firmware Flow of Low-Power LCD Operation
Active mode: Run LCD in PWM mode to get
better contrast and viewing angle
Go to Digital Correlation drive mode before
going to Deep-Sleep mode
Call the Deep-Sleep API
Go back to PWM mode when the processor
goes back to active mode
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PSoC® 4 Segment LCD Direct Drive
7
PSoC 4 User Interface Solution
This section shows how to create complete user interface (UI) solutions using just PSoC 4. A basic knowledge of
PSoC 4 CapSense is a prerequisite for this section. See the PSoC 4 CapSense Design Guide to understand the
basics of CapSense.
The CapSense feature in PSoC 4 offers unprecedented signal-to-noise ratio (SNR), best in class waterproofing, and
a wide variety of sensors such as buttons, sliders, track pads, and proximity sensors. You can use the segment LCD
drive together with CapSense and low-power modes to create elegant, reliable, power-efficient, and easy-to-use UI
solutions.
Figure 9 shows an example UI in which PSoC drives a segment LCD and scans a touch panel. The touch panel
consists of two CapSense buttons and a slider.
Figure 9. Example of PSoC 4 User Interface
Segment LCD
PSoC 4
Touch Panel
CapSense
Button
CapSense Slider
CapSense
Button
CapSense cannot scan sensors in Deep-Sleep mode, so the device must wake up periodically to scan the sensors.
PSoC 4 must remain in the Active mode while scanning the sensors. To save power, the device should spend more
time in Deep-Sleep mode and less in the Active mode.
If CapSense detects a touch, PSoC 4 stays in the Active mode and scans each sensor individually to read the touch
panel input. The device returns to Deep-Sleep mode when the panel becomes inactive again.
PSoC 4 CapSense can bundle several sensors together and scan as a single sensor. This reduces the total time
required in Active mode.
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PSoC® 4 Segment LCD Direct Drive
Figure 10 shows an example firmware flow of a low-power user interface (UI) solution.
Figure 10. Firmware Flow of a Low-Power UI Solution
Scan all CapSense sensors individually.
Change LCD drive mode to PWM
Check if the touch panel is
inactive
No
Yes
Change LCD drive mode to Digital
Correlation. Enter Deep-Sleep mode.
Timed wakeup
Bundle all the sensors together and
scan as a single sensor
Touch
detected ?
No
Yes
See the “Segment LCD and CapSense User Interface” project for more details. This project demonstrates a user
interface with a 4-digit, 7-segment LCD, and a 5-element CapSense slider.
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PSoC® 4 Segment LCD Direct Drive
8
PSoC Creator Projects
This application note provides four example projects:
1.
Simple Segment LCD: This is a simple project to demonstrate basic usage of the PSoC Creator PSoC 4
Segment LCD Component.
2.
Low-Power Segment LCD: This project shows how to use the Segment LCD Component with very low power
consumption.
3.
Segment LCD and CapSense User Interface: This project shows how to create a complete user interface
solution using the Segment LCD and CapSense Components.
You can use any PSoC 4 kit or your own hardware to evaluate projects 1 and 2. Project 3 requires the Cypress
CY8CKIT-042.
All three projects require a VIM 404 segment LCD module, which has four 7-segment digits, three COM
electrodes, and 12 SEG electrodes. See Figure 17 on page 18 for a wiring schematic.
4.
8.1
Alphanumeric Segment LCD: This project takes advantages of the large number of GPIOs available in the PSoC
4100M / 4200M devices to drive a VIM-828 segment LCD module, which has eight 14-segment digits, four COM
electrodes, and 32 SEG electrodes. This project requires Cypress CY8CKIT-043 or CY8CKIT-046 and a VIM828 Segment LCD module.
Project 1: Simple Segment LCD
To create this project, do the following:
1.
Create a new PSoC 4 project. If you are new to PSoC Creator, see the PSoC Creator home page.
2.
Drag and drop a Segment LCD Component and a Clock Component into the TopDesign schematic. Connect
them together using a wire, as Figure 11 shows.
Figure 11. Connection of LCD and Clock
3.
Double-click the Segment LCD Component to open the configuration window.
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PSoC® 4 Segment LCD Direct Drive
4.
Configure the General tab in the Component configuration dialog. Choose the LCD drive settings as Figure 12
shows.
Figure 12. Segment LCD Configuration, General Tab
Set the number of common and segment lines to 3 and 12 respectively, to match the VIM 404 segment LCD
module.
Use PWM drive mode; see PSoC 4 Segment LCD Direct Drive on page 7.
Leave the remaining settings at their default values.
Select 1/2 bias because it provides good contrast on the VIM 404 segment LCD module.
Choose Type B waveform. Type B waveform consumes slightly less power than the type A waveform. For
more information on these waveforms, see the PSoC 4 Technical Reference Manual.
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PSoC® 4 Segment LCD Direct Drive
5.
Configure the Display Helpers tab. This tab maps SEG and COM electrodes to the display module. Use the
LCD module datasheet to configure this tab (see VIM-404).
The LCD module has four 7-segment digits. To add 7-segment display helpers, select 7 Segment in the Helpers
list box, and click the
button. The selected display feature is visible in the Selected helpers list box, as
Figure 13 shows.
Figure 13. Adding Display Helpers
The LCD module has four 7-segment digits, so add three more 7-segment digits by clicking the
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button.
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PSoC® 4 Segment LCD Direct Drive
6.
Drag a segment from a digit and drop it onto the pixel mapping table, as Figure 14 shows. See VIM-404
datasheet for the pixel mapping of the VIM 404 LCD module.
Figure 14. Pixel Mapping Procedure
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PSoC® 4 Segment LCD Direct Drive
7.
Repeat the process for each segment in the display. After mapping all of the pixels, the completed table appears
as shown in Figure 15.
Figure 15. Completed Pixel Mapping Table
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PSoC® 4 Segment LCD Direct Drive
8.
Click OK; the Segment LCD Component configuration is now complete. To assign the pins for the commons and
segments, open the .cydwr (design wide resources) file and assign pins as Figure 16 shows.
Note: The pin assignment shown here is for the CY8CKIT-042 development kit. If you’re using a different kit,
refer to the kit user guide and select the suitable pins that aren’t connected to any other peripherals on the kit.
Figure 16. Pin Assignment
9.
Wire the VIM 404 LCD glass to PSoC 4, as Figure 17 shows. This can be done on your own PCB, or you can
use the CY8CKIT-042 kit and an Arduino ProtoShield board.
Figure 17. PSoC 4 to LCD Module External Connections
3.3V
P0[6]
P0[0]
P3[7]
P3[1]
P3[0]
P3[4]
P2[3]
P2[6]
P2[7]
P1[0]
P3[5]
Vdd
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
VIM 404
PSoC 4
Vss
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P2[4]
P0[4]
P0[5]
P0[7]
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PSoC® 4 Segment LCD Direct Drive
10. Add firmware to the project. To create a scrolling display of numbers 1, 2, 3, ..., 9, 0, add the code in Code 1 to
main.c.
The Segment LCD Component offers a ready to use API. For details on the API functions, see the PSoC 4
Segment LCD Component datasheet.
Code 1. Scrolling Numbers on the LCD
#include <device.h>
/* Macro for a black space on the 7-segment LCD */
#define BLANK (16u)
/* Macro for scrolling length */
#define SCROLL_LENGTH (14u)
/* Macro for initial scrolling value */
#define INITIAL_VALUE (0u)
/* Define the numbers used for scrolling the 4-digit display */
#define SCROLL0 (0u)
#define SCROLL1 (1u)
#define SCROLL2 (2u)
#define SCROLL3 (3u)
#define DIGIT0
(0u)
#define DIGIT1
(1u)
#define DIGIT2
(2u)
#define DIGIT3
(3u)
/* Define the loop delay */
#define LOOP_DELAY (512u)
void main()
{
/* This variable is used to index the character array */
uint8 index = 0;
/* Array of scrolling numbers including blank spaces to improve visibility */
uint8 numbers[] = {BLANK, BLANK, BLANK, BLANK,
1, 2, 3, 4, 5, 6, 7, 8, 9, 0, BLANK, BLANK, BLANK};
/* Starts the Segment LCD Component */
LCD_Start();
for(;;) /* do forever */
{
/* Scroll the blanks and numbers stored in the array, from right to left */
for(index = INITIAL_VALUE; index < SCROLL_LENGTH; index++)
{
/* Print the numbers on the LCD glass */
LCD_Write7SegDigit_0(numbers[index + SCROLL3], DIGIT0);
LCD_Write7SegDigit_0(numbers[index + SCROLL2], DIGIT1);
LCD_Write7SegDigit_0(numbers[index + SCROLL1], DIGIT2);
LCD_Write7SegDigit_0(numbers[index + SCROLL0], DIGIT3);
/* Give delay for a visible scrolling */
CyDelay(LOOP_DELAY);
}
}
}
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PSoC® 4 Segment LCD Direct Drive
11. Make sure that PSoC 4 is operating from 3.3 V VDD supply. Program the device and view the LCD display to verify
the output. You can see numbers 1, 2, 3, ..., 9, 0, scrolling from right to left as Figure 18 shows.
Figure 18. LCD Display Module Scrolling Numbers
If the contrast of the display is too high, reduce the contrast in the Segment LCD Component and program the device
again.
8.2
Project 2: Low-Power Segment LCD
This project is a modification of Project 1, for lower average power.
To reduce power consumption, PSoC 4 stays in Active mode just long enough to update the display and scroll the
numbers one place, which takes approximately 720 µs. The device then goes into the Deep-Sleep power mode for
the next 512 ms. Figure 19 shows the timing diagram and Figure 20 shows the firmware flow.
With this technique, PSoC 4 consumes an average current less than 11 µA. Table 4 shows a comparison of
approximate power consumption between the two projects.
Table 4. Power Comparison Between Projects
Power Mode
Active current
Deep-Sleep current
Average current
Project 1
This Project
2.7 mA
2.7 mA
n/a
7 µA
2.7 mA
10.9 µA
Figure 19. Project 2 Timing Diagram
Deep-sleep
512ms
Current
2.7mA
720µs
Active
7µA
time
Powered On
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PSoC® 4 Segment LCD Direct Drive
Figure 20. Project 2 Firmware Flow
Change LCD drive mode to Digital
Correlation
Go to Deep-Sleep
Wait 512mS
Come back to Active
Change LCD drive mode to PWM.
Display next digit.
This project uses the Global Signal Component to generate a watchdog timer (WDT) interrupt. Configure the
Component as Figure 21 shows. The WDT is configured to generate an interrupt every 512 ms. Figure 22 shows the
TopDesign schematic of this project.
Figure 21. Global Signal Component Configuration
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PSoC® 4 Segment LCD Direct Drive
Figure 22. Project 2 LCD TopDesign Schematic
To test the project, program the device, connect the display as in Project 1 (Figure 17) and view the output. You will
still see a scrolling display; however, power consumption for this project is significantly reduced.
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22
PSoC® 4 Segment LCD Direct Drive
8.3
Project 3: Segment LCD and CapSense User Interface
This project demonstrates a complete user interface (UI) consisting of CapSense touch sensing and a segment LCD
for display. UI controllers spend most of their time, and hence power, waiting for user input. To implement a power
efficient design, the PSoC 4 periodically enters Deep-Sleep low-power mode.
Note: This project uses manual tuning of CapSense widgets to achieve very low scan time and power consumption.
Knowledge of CapSense manual tuning is a prerequisite for this project. See the PSoC 4 CapSense Design Guide to
understand manual tuning.
This project is a modification of Project 2 to add CapSense capability. Figure 23 shows the timing diagram, Figure 24
shows the TopDesign schematic for this project, and Figure 25 shows the firmware flow.
In this project, PSoC 4 stays in the Deep-Sleep mode for only 128 ms, so that CapSense scans the sensors
frequently enough to detect fast touches. Upon wakeup, CapSense bundles together all slider elements and scans
them as a single proximity sensor. If any slider element is touched, the proximity sensor detects a touch and then
each element is scanned individually to determine slider touch position. The slider position is then displayed on the
LCD.
If all the CapSense widgets are inactive for 128 ms after a touch is detected, the device returns to Deep-Sleep mode.
In the absence of touch, the average current consumed by PSoC 4 is less than 21 µA.
Figure 23. Project 3 Timing Diagram
Deep-sleep
128ms
Current
3.5mA
500µs
Active
7µA
time
Powered On
Figure 24. Project 3 TopDesign Schematic
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23
PSoC® 4 Segment LCD Direct Drive
Figure 25. Project 3 Firmware Flow
Change LCD drive mode to PWM
Scan the slider and display the finger position.
Sensor inactive
for 128 mS ?
No
Yes
Change LCD drive mode to Digital
Correlation. Enter Deep-Sleep mode.
WDT wakeup after
128 mS
Bundle all the sensors together and
scan as a single sensor
Touch
detected ?
No
Yes
To test the project, connect the LCD as Figure 17 shows, touch the slider, and confirm that the LCD displays the
slider position. When the slider is inactive, the LCD displays “dSLP” to indicate the Deep-Sleep mode of the device.
Note that the default CapSense parameters are manually tuned for CY8CKIT-042 under a given set of conditions.
You should manually tune the CapSense again if the touch response is poor. The other alternative is to use
SmartSense™, a firmware algorithm that automatically sets all parameters to optimum values. See the PSoC 4
CapSense Design Guide for details. Note that using SmartSense increases power consumption. The approximate
average power consumption for this project with SmartSense is 40 µA.
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PSoC® 4 Segment LCD Direct Drive
8.4
Project 4: Alphanumeric Segment LCD
This project takes advantage of the large number of GPIOs available in the PSoC 4100M/4200M/4100L/4200L
devices to drive a VIM-828 segment LCD module, which has eight 14-segment digits, four COM electrodes, and 32
SEG electrodes. This project requires Cypress CY8CKIT-043 or CY8CKIT-046 and a VIM-828 LCD.
The segment LCD Component provides rich APIs to display strings on 14-segment alphanumeric displays. This
project shows a static text “PSoC4200” displayed on VIM-828. See the PSoC Creator project for more details. Table
5 gives the pin mapping information for wiring VIM-828 to CY8CKIT-43 and CY8CKIT-46.
Table 5. Wiring Information
LCD Pin Number
LCD Pin Function
CY8CKIT-43 Connection
CY8CKIT-046 Connection
1
COM3
P0[7]
P2[0]
2
SEG0
P0[6]
P2[1]
3
SEG1
P0[5]
P2[2]
4
SEG2
P0[4]
P2[3]
5
SEG3
P0[3]
P2[4]
6
SEG4
P0[2]
P2[5]
7
SEG5
P0[1]
P3[6]
8
SEG6
P0[0]
P3[7]
9
SEG7
P7[1]
P9[0]
10
SEG8
P4[0]
P9[1]
11
SEG9
P3[7]
P9[2]
12
SEG10
P3[6]
P9[3]
13
SEG11
P3[5]
P6[1]
14
SEG12
P3[4]
P6[0]
15
SEG13
P3[3]
P6[3]
16
SEG14
P3[2]
P4[0]
17
SEG15
P3[1]
P4[1]
18
COM2
P3[0]
P3[4]
19
COM0
P6[5]
P6[5]
20
SEG16
P6[4]
P5[5]
21
SEG17
P6[2]
P5[6]
22
SEG18
P6[1]
P4[4]
23
SEG19
P6[0]
P4[5]
24
SEG20
P2[7]
P4[6]
25
SEG21
P2[6]
P4[7]
26
SEG22
P2[5]
P3[1]
27
SEG23
P2[4]
P3[0]
28
SEG24
P1[3]
P8[7]
29
SEG25
P1[2]
P8[6]
30
SEG26
P1[1]
P8[5]
31
SEG27
P1[0]
P8[4]
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PSoC® 4 Segment LCD Direct Drive
9
LCD Pin Number
LCD Pin Function
CY8CKIT-43 Connection
CY8CKIT-046 Connection
32
SEG28
P5[5]
P8[3]
33
SEG29
P5[3]
P8[2]
34
SEG30
P5[2]
P8[1]
35
SEG31
P5[1]
P8[0]
36
COM1
P5[0]
P5[6]
Summary
This application note demonstrated the segment LCD drive in PSoC 4. The combination of robust capacitive touch
sensing and best-in-class low-power capabilities make PSoC 4 an ideal choice for a low-power, single chip, user
interface solution.
This application note also gives four example projects to get started with the PSoC 4 segment LCD, show low-power
operation, and demonstrate a complete user interface.
Note that PSoC 4 has many additional features such as programmable analog and digital, 32-bit ARM Cortex-M0
microcontroller, and serial communication blocks that allow you to create an entire system solution around PSoC 4.
About the Authors
Name:
Nidhin MS
Title:
Applications Engineer Sr.
Background:
Nidhin graduated from GEC Thrissur, with a Bachelor's degree in Electronics and Communication
Engineering. His technical interests are analog signal processing, low-power design, and capacitive
touch sensing.
Name:
Rahul Raj Sharma
Title:
Applications Engineer
Background:
Rahul graduated from RNSIT Bangalore, with a BE in Electronics and Communication Engineering.
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Document No. 001-87391 Rev. *C
26
PSoC® 4 Segment LCD Direct Drive
Document History
Document Title: AN87391 - PSoC® 4 Segment LCD Direct Drive
Document Number: 001-87391
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
4129400
NIDH
09/18/2013
New application note
*A
4602278
NIDH
12/19/2014
Updated the example project. Added mention of SmartSense for project 3 with
power numbers.
*B
4797445
NIDH
06/24/2015
Updated Feature List , Basics of segment LCD, and Table -1 for PSoC 4A-M
Added Project 4
Updated template
Added PSoC Resources section
*C
5068119
NIDH
02/09/2016
Added PSoC 4 L series, CY8CKIT-046 information
Added CY8CKIT-046 to pin mapping table
Updated projects to PSoC Creator 3.3 CP1
Linked PSoC 4 low power AN in the introduction
Added a note for Table-2 indicating that these are approximate power numbers
that may vary with device family, LCD and firmware
Added step-by-step instructions for Low-Power Operation to section 6.3
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Document No. 001-87391 Rev. *C
27
PSoC® 4 Segment LCD Direct Drive
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