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You can use your iPad as a digital drawing pad when you need to illustrate something and you don’t have pen and paper handy. It’s D IDVWHU PHWKRG RI GUDwLng, DnG yRX save paper and ink at the same time. Designers aren’t the only ones who can EHnHfiW IURP D GLgLWDO GUDwLng SDG. IW LV gUHDW IRU SUHVHnWDWLRnV, GHVLgn VWXGLHV, SURGXFW FRnFHSW GHVLgnV, LOOXVWUDWLRnV, storyboards and more.
AV WKH L3DG LV TXLWH HxSHnVLvH, here we present a digital drawing pad which is made with the help of a graphic liquid-crystal display (GLCD) having controller hS0108 and a fourwire resistive touch screen. GLCD and touch screen are interfaced with microcontroller ATmega1S.
Touch screen
A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area. It is sensitive to the touch of D KXPDn fingHU, KDnG, SRLnWHG fingHU nail and passive objects like stylus. It is a two-dimensional sensing device that is made of two sheets of material separated by small spacers.
There are three main touch screen WHFKnRORgLHV: UHVLVWLvH, FDSDFLWLvH DnG surface acoustic wave. Here we used resistive touch screen.
Resistive touch screen. The resistive touch screen (refer Fig. 1) consists RI D flHxLEOH WRS ODyHU PDGH RI SROyHWKylene and a rigid bottom layer made of glass. Both the layers are coated with a conducting compound called indium tin oxide and then spaced with spacers.
:KHn WKH PRnLWRU LV RSHUDWLRnDO, Dn HOHFWULF FXUUHnW flRwV EHWwHHn WKH WwR ODyHUV. :KHn D WRXFK LV PDGH, WKH flHxLEOH VFUHHn SUHVVHV GRwn WR WRXFK the bottom layer. A change in electrical current is hence detected and the coordinates of the point of touch calculated by the controller and parsed into readable signals for the operating system to react accordingly.
The four-wire resistive touch screen uses both the layers to calculate the axes information of the touch. Touch measurement is a two-step process. The x-coordinate of the touch point is calculated by creating a voltage gradient on WKH flHxLEOH ODyHU, DnG WKH y-FRRUGLnDWH is determined by creating a voltage gradient along the bottom layer.
The analogue values related to the position of touch are fed to ATmega 1S and processed using its inbuilt analogue-to-digital converter (ADC).
GLCD. This LCD can display images as well as text. The LCD used here has the display format of 1O8×S4 dots. A 1O8×S4 LCD implies 1O8 columns and S4 rows. In total there are 1O8×S4=10O4 pixels. The 1O8×S4 LCD is divided equally into two halves. bach half is controlled by a separate controller (hS0108 in this case) and consists of eight pages.
Circuit description
Fig. O shows the circuit for the digital drawing pad. It comprises microconWUROOHU ATPHgD16, UHgXODWRU 7805, UHVLVWLvH WRXFK VFUHHn, gUDSKLFDO /CD DnG D few discrete components.
The ATmega1S is a low- power CMlS 8-bit microcontroller based on the AVR-enhanced RISC architecture. The AVR core combines a rich instruction set with 3O general-purpose working registers. All the 3O registers are directly connected to the DULWKPHWLF ORgLF XnLW, allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more FRGH-HIfiFLHnW.
The ATmega1S has 1S kB of in-system programmable flDVK SURgUDP PHPRUy, 512 EyWHV RI ((3R20, 1NB 6RA0, 3O general-purpose LnSXW/RXWSXW OLnHV, 3O general-purpose wRUNLng UHgLVWHUV, three flexible timers/counters with FRPSDUH PRGHV, Ln-