Help with a flip-flop combination lock circuit

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Joined Feb 8, 2010
I have an aftermarket remote start module in my car that has its own remote. The unit also has a test lead that will start the car when it is grounded momentarily. Since my car has an OEM remote to lock and unlock the doors built into the key, I would like to build a simple circuit possibly using CD4013 flip-flops to use a combination of lock and unlock pulses (like lock-lock-unlock-lock) within a set period of time to close a relay to ground the test wire. I would pick up the pulses from the 12 volt lines going to the door lock solenoid in the drivers door. Logically, when the first lock pulse comes in, it would trigger the first flip-flop and start a timer. If the following pulses arrive within the time period in the proper order, the relay would energize. If not, the circuit would reset and wait for the next lock pulse. I found a schematic as a starting point and revised it to come up with the attached. It doesn't guarantee the exact combination (lock-lock-unlock-lock) but it does force two locks only before the unlock. I am still having a problem with the auto-reset after the solenoid is activated. According to the original lock circuit, the R12/C2 timer circuit is supposed to reset the lock through diode D1. If I close SW4, the circuit doesn't work at all. If I leave it open, the circuit works but does not auto-reset. Any ideas?

Also, what would be the easiest and/or best way to put a timer on the overall circuit that would require the proper input (lock-lock-unlock-lock) within 5 seconds or the circuit resets?



Joined Jul 17, 2007
Hello holabr,

Unfortunately, your request for help is in conflict with the Terms of Service, which in part state:

6. Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:
  • Any kind of over-unity devices and systems
  • Automotive modifications
  • Devices designed to electrocute or shock another person
  • LEDs to mains
  • Phone jammers
  • Rail guns and high-energy projectile devices
  • Transformer-less power supplies
Since discussion of automotive modification topics is specifically prohibited, we cannot go any further with your topic.

In the Electronic Resources forum, there is a "sticky" thread which has a short list of member-suggested alternative forums where you might find support for your project.
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