INTERFACING 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.
PPIO2899 Manual | 27 |
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