B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 28)

PPIO2899 Manual
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
27
I
NTERFACING TO THE
PPIO
Each output of the PPIO is capable of handling currents as high
a 500 mA when the output is low. This means that you can connect
a relay or a light or other load between the output and a positive
power supply voltage. See Figure 3 for an example output.
Whenever the PPIO output in the example is LOW the relay will turn
ON and close the contact. To turn ON the relay you should use the
force I/O ON portion of Table 2. Of course, if you use a 24 volt relay,
you will need a 24 volt power supply. The PPIO will control devices
up to a maximum of 50 volts DC.
Figure 3
Each input of the PPIO works with voltages up to 50 volts DC
with a threshold of 2.5 volts. This means that to force a LOW the
PPIO input must be below 2.5 volts. To force a HIGH the PPIO input
must be above 2.5 volts. If you leave the PPIO input open it is the
same as a HIGH input (above 2.5 volts). See Figure 4. In the
example if the temperature is below 72 degrees the thermostat will
be open and the PPIO input will be HIGH. The bit that is read into
the computer will be a ZERO (negative true logic). When the
temperature goes above 72 degrees the thermostat closes and
forces the PPIO input to ground giving you a ONE in the computer.