SSR-RACK24 - 74LS640 – Pull-down DIO device
The input signals to the SSR-RACK will read around 1.33V with no connection. The device
driving the rack, at least in input mode, must be able to sink this voltage below 0.8V. In the case
of the miniLAB 1008, there is a 47kΩ resistor pack that does not sink the required voltage. The
following results using a 10k Ω resistor and a 2.2 kΩ resistor should work. The 10 kΩ resistor
voltage value is an estimate.
Resistor
kΩ
2.2
10
47
Voltage
V
0
0.13
0.8
We recommend, per the PCI-DIO24 manual, a 2.2 kΩ resistor.
The miniLAB 1008, if configured in the pull-down configuration, should be converted to the 2.2
kΩ resistor or the 10 kΩ resistor.
The 2.2 kΩ resistor is working with the miniLAB 1008. This adds a drop of 0.114mA with
respect to the 47 kΩ resistor.