PWR−ISO Circuit - Atlas Scientific

PWR−ISO Circuit
V3.0
TM
Reading electrochemical events in water that is electrically noisy can be a bit tricky. Pumps,
heaters, chillers even overhead lights can leak electrical noise into a seemingly closed system.
When using a hand held device, such as a pH meter it is automatically immune from electrical
noise, this is because its battery powered and does not share a common ground with the rest
of your system. To stop electrical noise you will need to supply your circuitry with isolated
power and data lines. The Atlas Scientific PWR-ISO is a simple 12 pin module that will eliminate
electrical noise in your sensor application.
• Sources up to 150ma of fully isolated power
• Will work with UART or I2C protocols
• Only 32ma current draw in quiescent mode
• Dimensions: 26.5mm X 21mm X 20.35mm (1.04" X 0.83" X 0.80")
Unisolated power and data lines connect on the IN side.
Isolated power and data come out on the OUT side.
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PWR−ISO Circuit
V3.0
Pin Out
GND
Return for the DC power supply. GND (& Vcc)
must be ripple and noise free for best operation.
5V
Operates on 5V (Only 5V)
A
Data path A, is an electrically isolated data path that can be used for UART, I2C
or SPI protocols. This pathway is generic, and can be any part of the communication protocol
such as: RX,TX, SCL, SDA, MISO, MOSI or SCKL.
B
Data path B, is an electrically isolated data path that can be used for UART, I2C
or SPI protocols. This pathway is generic, and can be any part of the communication protocol
such as: RX,TX, SCL, SDA, MISO, MOSI or SCKL.
X
Generic electrically isolated I/O line. This line can be used for any I/O function where
electrical isolation is required. (This pin can source upto 50mA)
Y
Generic electrically isolated I/O line. This line can be used for any I/O function where
electrical isolation is required. (This pin can source upto 50mA)
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PWR−ISO Circuit
V3.0
Data Paths
The data lines marked A and B can be used to isolate UART, I2C or
SPI data protocols. The data path moves strait through the device
where A goes to A and B goes to B.
X
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
V3
X
Y
X
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
OUT
V3
X
Y
OUT
The I/O lines marked X and Y can be used to isolate generic I/O lines.
The data path moves strait through the device where X goes to X
and Y goes to Y.
1 0
0 1
1 0
X
Y
1 0
0 1
1 0
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
V3
X
Y
1 0
0 1
1 0
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X
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
OUT
V3
X
Y
OUT
0 1
1 0
0 1
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PWR−ISO Circuit
V3.0
X
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
V3
X
Y
OUT
The Atlas Scientific PWR-ISO Circuit is designed to eliminate electrical noise. Electrochemical
sensors are very sensitive devices by design. This sensitivity is what gives them their accuracy
and precision however, it also makes them susceptible to electrical noise. Most times this
noise comes from pumps or lighting systems and cannot be detected by a multimeter.
An electrochemical sensor that is picking up electrical noise will show readings that are bouncing
and can be significantly out of range.
0.0
VDC
Pump
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PWR−ISO Circuit
V3.0
The Atlas Scientific PWR-ISO provides power and data line isolation. This isolation will make it
immune from electrical noise. This is because the electrochemical sensor is now connected to
its own power supply and no longer shares its ground line with the device that was creating
the electrical noise (pump, lights etc.)
X
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
V3
X
Y
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OUT
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5
PWR−ISO Circuit
V3.0
Wiring Diagrams
MCU
1010101
I/O I/O RX TX
5V
1010101
X
Y
5V
GND A
B
5V
GND A
B
IN
X
PWR-ISO
V3
TM
Atlas-Scientific.com
X
Y
Y
5V
GND A
B
5V
GND A
B
IN
PWR-ISO
V3
OUT
X
Y
OUT
TM
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PWR−ISO Circuit
V3.0
Ground Loops
The Atlas Scientific PWR-ISO cannot shield against ground loops. A ground loop can
simply be described as a situation where a systems ground line is not actually 0 volts.
A ground loop can have a significant effect on the reliability of your readings.
No Ground Loop
5.0
X
VDC
Y
5V
GND A
B
IN
5V
Difference is 5V
PWR-ISO
V3
X
Y
5V
GND A
B
X
Y
5V
GND A
B
OUT
0V
Ground Loop
5.0
VDC
IN
5.2V
Difference is 5V
PWR-ISO
V3
X
Y
5V
GND A
B
OUT
0.2V
Identifying and resolving ground loops can be very complicated, and is beyond
the scope of this data sheet.
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PWR−ISO Circuit
V3.0
This schematic shows exactly how we isolate data and power using two parts, the
data isolator part # SI8600, and the Power isolator part # ROE-0505S.
The SI8600 is a digital isolator with two bidirectional channels, which makes it excellent
for use with I2C and UART protocols. This Part requires isolated power and pull ups
on both channels on the isolated and non-isolated inputs. Pull up resistors can be
anything from 3k to 10k.
The ROE-0505s is an isolated DC/DC converter that can handle 5V @ 1W. This part
uses a Transformer that provides a 1:1 ratio (5V in and 5v out) however we have seen
that 5V in produces 5.4V out and we recommend using a 5V regulator on its output.
We use part# NCP698SQ50T1G. Note: the Isolated Ground is different from the
non-isolated Ground, these two lines should not be connected together.
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