Measurement Computing DataShuttle - Manual (Page 65)

DataShuttle and DynaRes 11-12-01 Introduction to Terminal Panels 6-9
The terminals for that I/O have now changed their function from low voltage I/O to high voltage isolated
I/O. The two terminals become one input channel (high and low lines), or one output channel (like relay
contacts), depending on the type of module you have installed.
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When using these terminals as input lines, be sure to connect the positive line to the
old OUT terminal and the negative line to the old IN terminal. Failure to do this will
result in the module not switching.
Installing Pull-up Resistors
As noted in the Applications Reference Manual and previously in this manual, the digital outputs are open
collector and must have a power source connected in order to drive loads. Merely connecting the output
terminal through a load (such as a bulb) and then to digital ground will not work. In this case, a pull-up
resistor connecting the output terminal to a power supply will complete the circuit.
This pull-up resistor is installed in position R8, as shown in Figure 10(b), which connects the output to the
board’s +5V power supply. The Figure on page 6-2 shows the physical location of R8 on the T31 terminal
panel. Note that R8 is not available on the T71 and may have to be installed manually between the +5V
supply and the output terminal in question.
To install this resistor, push the resistor ends through the holes for R8 (from the terminal side) until the
resistor lies flat with the panel surface. On the backside, solder the wires to the holes. Clip off the extra wire
with pliers. This connection does not require any additional traces to be cut. Use a 4.7K resistor to give 1
mA current flow or a 2.3K resistor to give 2mA current flow.
Troubleshooting Q & A
1. Problem: Why can’t I measure any voltage change with my voltmeter on my digital output?
Action: With nothing but a voltmeter connected, this is normal (except on T71 panels, which have
pull-ups installed). The digital outputs are termed “open collector.” These kind of outputs do not
supply any voltage, it must be supplied from another source. This allows the flexibility to use any
supply voltage up to 30V. The easiest way to see the state of an output terminal is to check the state of
the input terminal with a voltmeter.
2. Problem: My digital inputs are “high” with nothing connected to them.
Action: This is normal. The digital inputs are pulled up to about 1.5 volts by leakage from the
LS7407 chips. This is enough to read as a logic high. You can pull them down with a 470
Ω resistor to
ground. If you remove the LS7407 chips the inputs will be low, but the outputs will be disabled.
(NOTE: On T71 panels, inputs will default to low if R10 is moved to GND.)
3. Problem: Can I get an output signal from the input terminals?
Action: Yes, you can use an input terminal to drive light loads such as a TTL input (except on T71
panels).
4. Problem: What should I do with the jumpers connecting the analog input to COM?
. Action: In general, it is best to leave them connected as shipped. Unless using thermocouples
connected to a common ground point on multiple units