I have a project which requires me to interface a 24VDC output module (PLC) with a rather outdated 5V TTL input module.
From the schematics of the old module I can draw the conclusion that it uses +5V as a reference for all the inputs and 0V to activate the input.
I found the following module: MICROOPTOMOS 12-28VDC/5VTTL which I can activate using a 24V signal and it outputs 5V TTL.
The schematic of the module is this:
My question is, how would I go about wiring the module in the way that it "pulls" to the ground the 5V TTL input in order to activate it?
Best Answer
Judging by the Schmitt trigger symbol in the receiver this module will output a 'high' when the input is on. You want the reverse. You could use an open-collector transistor to do this or you could reverse the output logic in the PLC. Connect up to your +5 V and 0 V and wire OUT to the TTL input.
Alternative solutions:
simulate this circuit – Schematic created using CircuitLab
Figure 1. Three options.
Figure 2. Use a DIN rail component carrier to make an industrial standard custom module for your interface circuits.
From the comments:
Be careful here. You need to ensure that your solution can't put 24 V DC onto a 5 V input. A typical 24 V PLC output will give 24 V or nothing - and nothing means open-circuit, it doesn't mean 0 V. You need a level converter (24 V to 5 V) and then you need to check your logic is the right direction. Since the PLC is active high and TTL is typically active low you may need to invert the logic. If the interface will do that you don't need to do anything else. If the interface won't then have it done in the PLC logic.