Microcontroller interfacing with an I/O card

For this industrial electronics project I have I have to interface a computers digital outputs from a microcontroller to an I/O card using potter and brumfield modules. The problem I am encoutering is that I can't change the digital output voltage to a negative properly im running it into 741 set as an inverter, the digital high works as planned but when it is supposed to be a low voltage it still sends out the -5 voltage to the I/O card turning it on, any ideas would be appreciated.

Post the schematic.

William56 said:

For this industrial electronics project I have I have to interface a computers digital outputs from a microcontroller to an I/O card using potter and brumfield modules. The problem I am encoutering is that I can't change the digital output voltage to a negative properly im running it into 741 set as an inverter, the digital high works as planned but when it is supposed to be a low voltage it still sends out the -5 voltage to the I/O card turning it on, any ideas would be appreciated.

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Are these the modules you are using?
https://relays.tycoelectronics.com/datasheets/IAC_DS.pdf
(The same devices come four to a package, with a "Q" somewhere in the part-number: the remarks below apply, but with different pin #s)

What is needed is to apply a voltage on pins 3 and 4, with pin # positive WRT pin 4. The voltage is usually in the part-number: "OAC24" is an AC-output that needs 24 Volts and "ODC5" is a DC-output that takes 5V input. The source must be able to supply at least 10 mA.

There are two ways to activate the module:
1 Connect pin 4 to ground and apply a positive voltage to pin 3
2 Connect pin 3 to the supply and pull pin 4 down to ground (usually an open-collector transistor.)

These output modules are often mounted on a PC-board that carries 4,8,16 or 24 modules: these have all "pin-3"s connected together so that method [2] above must be used. here's an example:
https://lgrws01.grayhill.com/web1/images/ProductImages/IO_Racks_8_Channel.pdf