using a 4013 to latch a relay on/off

[geobee]

Hi all. Like to use a 4013 flip flop to drive a relay on/off in latch mode. Managed to make up a little circuit using a transistor to drive the relay, but I am wanting to trigger the  input of the 4013 from the trigger output of one of those little obstacle avoidance  modules off Ebay. The issue is, the trigger output is sitting at the supply volts of 5, but when connected to the input of the 4013, it drops to 3 volts before the it senses anything in front of it. I am going into pin 3 of the IC. Maybe someone has a better idea of a circuit. I need to reverse a model train on a section of track, so need to drive a DPDT relay to do the track supply switching. Any help would be much appreciated.

[Zero999]

That sounds like it should work. The 4013 has a high input impedance, so won't load the output of whatever it's connected to down.

Have you used suitable a decoupling capacitor and connected the inputs of the unused parts to either supply rail?

[geobee]

Many thanks. I did tie the unused pins to ground, but the cap is missing in my design. Will chase that up.

[Terry Bites]

Note that you need a clean clock (and data) signal to get this to work. if youve set up the 4013 to toggle (T-Type FF) then will flap in the wind every time dirty clock is applied. The state of D must be set 40ns before pin 3 goes high. If you are driving pin 3 with more than Vdd (even accidentally) the IC could latch up. If mad current is drawn then SCR latchup is occuring. See https://en.wikipedia.org/wiki/Latch-up.A small series resistor from clock source to pin 3 will help, say 51k.
put a bypass cap to ground as close to pin 14 as you can get it. 10-100n.
Can a 4013 provide enough base drive to your transistor. It can only source or sink a couple of mA from Q or /Q? What value of base resistor have you got. Have you put a diode across the coil to stop back emf killing your circuit?