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Design of a Digital Choral Folder
panel is updated. The concept of an electrical switch is one of the foundations of
electrical engineering. The most basic form of a switch is a physical one that actually
disconnects/reconnects the wires in a circuit. However, the simplest electrically
controlled switch without moving parts is the transistor. The invention of the field-effect
transistor in the early 1900s sparked the modern era of electronics, and is a key ingredient
in nearly every modern electrical device, from personal computers to audio equipment,
even including the E-Ink panel used in this project. Transistors are three terminal devices
which can be combined to influence an input signal and achieve all different types of
output characteristics. One of their most common applications is as an electrical switch.
Both analog and digital switches have been developed extensively using transistors and
are available as stand-alone ICs. There are many kinds and variations of electrical
switches, two of which are explained in this section.
D-Latch. A data latch, or d-latch, also called a “transparent latch” is an electronic
component which can be used as a switch. Basically, a d-latch takes a digital signal input
and passes it through unchanged while the device is enabled. When the latch is disabled,
the previous value on the output of the latch is preserved and a change in input is ignored
on the output. A data latch is a good way to switch a digital signal, but it is not meant for
analog signals. The major limiting factor of a d-latch is its response time – the time
required for a change in input to be reflected on the output.
Buffer Amplifier. An operational amplifier, or op-amp, is an analog circuit component
which passes an input signal through with some amplification, or gain. A unity gain
buffer, or voltage follower, has a gain of 1. Its logic symbol is shown in figure 11. The
output of the unity gain buffer will be nearly an exact copy of the input. However, when
the buffer is disabled there is no output on the device at all. The important limits on a
non-ideal buffer are its response time and its bandwidth response.
Figure 11: Buffer Logic Symbol
3.5 Software Development on the E-Ink Kit
The E-Ink development kit comes with a working computer system to drive the display.
Software may be written for this system to do all sorts of things. The system is based on
the Linux kernel, which may be downloaded and modified for any purpose under the
GPL. The kit also includes software development tools called Thinspace, which are a
simple set of scripts and programs that interact with the kit hardware. This section will
cover the basics of the Linux system on the E-Ink kit, the Thinspace development tools,
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