User Manual

Page 26
Hexiwear Workstation
OTHER MODULES
ADC inputs
Digital signals have two discrete states, which are decoded as HIGH and LOW, and
interpreted as logic 1 and logic 0. Analog signals, on the other hand, are continuous,
and can have any value within defi ned range. Analog to digital converters (ADC) are
specialized circuits, which can convert analog signals (voltages) into a digital form.
The digital value of the conversion is linearly dependent on the input voltage value.
Most modern microcontrollers have one or more internal ADC sections.
Some of the most important characteristics of the ADC are it’s conversion time and
resolution. Conversion time determines how fast can a sample can be taken - how
fast an analog voltage can be represented in the form of a digital value. Resolution
represents a number of discrete steps that supported voltage range can be divided
into. It determines the sensitivity of the ADC. Resolution is represented by the
maximum number of bits that the conversion value can take. For example: if ADC
has 10-bit resolution, the maximum value that can be written with 10 bits is 1024
(decimal). This means that the measured voltage range, for example from 0-3.3V, can
be divided into 1024 discrete steps of about 3.22mV (3.3V / 1024 = 0.00322V), so the
smallest step of this conversion would be 3.22mV, and it represents the sensitivity of
a particular ADC.
The Hexiwear Workstation board provides an interface in the form of one potentiometer, which acts as a voltage
divider. One end of the potentiometer is connected to 3.3V, while the other end is connected to GND. This allows the selection of any voltage value in the range between GND and
3.3V. The potentiometer output is routed to a 2x4 header, which allows the selection of the pin to which the output voltage will be routed, by a jumper J1 (Figure 27).
VCC-3V3
R4
220
1 2
3 4
5 6
7 8
J1
HM 2x4
C1
100n
G3.6
G4.3
G0.1
G1.7
P1
10K
DATA BUS
OTHER MODULES
OTHER MODULES
ADC inputs
In order to connect the output of the
potentiometer P1 to G0.1, G1.7, G3.6, or
G4.3 pins, J1 jumper should be placed
in the desired position. By moving the
potentiometer knob, the output voltage
of the potentiometer can be selected in
the range from GND to 3.3V
Figure 27: ADC input with the schematic