# 'Invert' a logic low and logic high signal from a FM60 controller [closed]

We have an Outback FM60 controller which outputs 0 or 12V as a command, 0 for logic high, and 12 for logic low. I need to invert that for our solid state relay to output 12 for high and 0 for low. Is there a COTS module or assembly that can do this for me?

• Càn you connect the SSR between the output and +12 V instead between the output and ground? That will invert the logic for free. Mar 12 '20 at 23:57
• Nice try! that made us think for a little bit. If I'm understanding you correctly @Transistor no this is coming from the FM60 aux output and is used to control a NC-SSR on and off. If this were a typical relay it would work but since it's a SSR, wiring the low signal at 12v would require a 24v signal to turn it on not 0v. Mar 13 '20 at 0:15
• Why no link to FM60 user manual and page reference? Link to SSR datasheet? Hit the edit link below your question ... Mar 13 '20 at 7:24

simulate this circuit – Schematic created using CircuitLab

Figure 1. (a) Connecting an SSR for positive logic. (b) Connecting SSR for negative logic.

If I'm understanding you correctly, no this is coming from the FM60 aux output and is used to control a NC-SSR on and off.

To be very clear:

• NC (normally closed) means that power can flow through the output terminals when there is no input signal.
• NO (normally open) means that no power can flow until the input signal is given.

You have supplied no part numbers for the "NC-SSR" and I have never seen one. All commonly available SSRs are normally-open type because semiconductors require power to turn on. In Figure 1 you need to power D1 before the triac can turn on. See Omron FAQ for more on this. There are some small-signal NC-SSRs.

If this were a typical relay it would work but since it's a SSR, wiring the low signal at 12 V would require a 24 V signal to turn it on not 0 V.

No. See Figure 1.

• Thanks for the answer, it's an NC-SSR P/N is Crydom D2425-B. Mar 13 '20 at 18:03
• It's polite to give a datasheet link to save time for folks giving freely of their time to help you. As requested already, please add all the relevant information into the question not buried in the comments. Mar 13 '20 at 18:41