I'd like to actuate a relay using a controller output that is already in use by another part of my system. This output is supposed to stay true during normal operation, but I can flash it to false then back to true without affecting the function of anything else.
So my idea is to use the quick turn-off/turn-on of this output from my controller to actuate a bistable relay for another output, as I am running out of outputs on my controller. I've tried using a flip-flop in toggle configuration but the low-high transition of the clock signal is not affecting the outputs in any way.
Could this be because I am leaving the signal high and not actually giving it a "pulse"? Is there a maximum width associated with clock pulses?
I selected the SN74HC109 from TI and, according to the truth table, if I drive /PRE, /CLR and J high (5 V) and drive K low (0 V) then when CLK goes from 0 V to 5 V, it should swap the states of Q and /Q. But I am not seeing any changes to Q and /Q on the rising edge at all.
The datasheet is listed here: http://www.ti.com/lit/ds/symlink/sn54hc109.pdf