Ground, Vs, AIN, DAC, FIO, and MIO are all described earlier.
Vm+/Vm- are bipolar power supplies intended to power external multiplexer ICs such as the MAX4051A (maxim-ic.com). The
multiplexers can only pass signals within their power supply range, so Vm+/Vm- can be used to pass bipolar signals. Nominal
voltage is ±5.8 volts at no load and ±5.6 volts at 1 mA. Both lines have a 100 ohm source impedance, and are designed to provide
1 mA or less. This is the same voltage supply used internally by the UE9 to bias the analog input amplifier and multiplexers. If this
supply is loaded more than 1 mA, the voltage can droop to the point that the maximum analog input range is reduced. If this supply
is severely overloaded (e.g. short circuited), then damage could eventually occur.
PIN2/PIN20 (TX0/RX0) currently bring out the UART transmit and receive lines, but in the future will likely be used as current
sources.
2.12.1 - CB37 Terminal Board
The CB37 terminal board from LabJack connects to the UE9’s DB37 connector and provides convenient screw terminal access to
all lines. The CB37 is designed to connect directly to the UE9, but can also connect via a 37-line 1:1 male-female cable.
When using the analog connections on the CB37, the effect of ground currents should be considered, particularly when a cable is
used and substantial current is sourced/sunk through the CB37 terminals. For instance, a test was done with a 6 foot cable
between the CB37 and UE9, and a 100 ohm load placed from Vs to GND on the CB37 (~50 mA load). A measurement of CB37
GND compared to UE9 GND showed 5.9 mV. If a signal was connected to AIN0 on the CB37 and referred to GND on the CB37,
the UE9 reading would be offset by 5.9 mV. The same test with the CB37 direct connected to the UE9 (no cable) resulted in an
offset of only 0.2 mV. In both cases (cable or no cable), the voltage measured between CB37 AGND and UE9 GND was 0.0 mV.
When any sizeable cable lengths are involved, a good practice is to separate current carrying ground from ADC reference ground.
An easy way to do this on the CB37 is to use GND as the current source/sink, and use AGND as the reference ground. This works
well for passive sensors (no power supply), such as a thermocouple, where the only ground current is the return of the input bias
current of the analog input.
2.12.2 - EB37 Experiment Board
The EB37 experiment board connects to the LabJack UE9’s DB37 connector and provides convenient screw terminal access.
Also provided is a solderless breadboard and useful power supplies. The EB37 is designed to connect directly to the LabJack,
but can also connect via a 37-line 1:1 male-female cable.
2.13 - DB15
The DB15 connector brings out 12 additional digital I/O. It has the potential to be used as an expansion bus, where the 8 EIO are
data lines and the 4 CIO are control lines.
In the Windows driver, the EIO are addressed as digital I/O bits 8 through 15, and the CIO are addressed as bits 16-19.
These 12 channels include an internal series resistor that provides overvoltage/short-circuit protection. These series resistors also
limit the ability of these lines to sink or source current. Refer to the specifications in Appendix A.
All digital I/O on the UE9 have 3 possible states: input, output-high, or output-low. Each bit of I/O can be configured individually.
When configured as an input, a bit has a ~100 kΩ pull-up resistor to 3.3 volts. When configured as output-high, a bit is connected
to the internal 3.3 volt supply (through a series resistor). When configured as output-low, a bit is connected to GND (through a
series resistor).
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