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Circuit help. 555 Timers, Inverters, Transistors.

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peterfares

New Member
Hello, I am trying to design a a circuit and need help.
I have attached a diagram for a part of it that isn't working.

What I am trying to accomplish is that whenever DLS or DUS are pulsed I need the connection from DLA to FobARM and the connection from DUA to FobDISARM to be disconnected for some time. The CD4049UB is an inverter.

Can anyone tell why this isn't working? Thanks.
 

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BrownOut

Banned
What exactly isn't working? In order to tell if the transistors will work, we need to see all the connections. We can't tell anything about DLA, fobARM, etc. If you just want generic switches, try using relays instead of BJT's. The one you need disconnected would use the NC contacts or use an inverter to connect it.
 

peterfares

New Member
Ok, here is the whole circuit.

I realize I was vague with the initial question. There is a couple things not working correctly, such as the circuit between DLA and FobARM not being closed when pulsed, but I think I might have solved that actually. I am getting more 555s today as one of them burned, don't really know why.

Ok, what about this. All 6 of the inverters on the circuit are one chip with 6 inverters on it. When either DUS or DLS are pulsed, The inverter U8 is affected and the voltage dips below the threshold to activate the 555 it outputs to.
 

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MikeMl

Well-Known Member
Most Helpful Member
I think you are trying to use the transistors as relays. The base of a transistor is not isolated from its emitter, and that is what is tripping you up.
 
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peterfares

New Member
I think you are trying to use the transistors as relays. The base of a transistor is not isolated from its emitter, and that is what is tripping you up.

Should I just replace all 4 PNPs with relays? How fast do relays switch? When DLS or DUS are pulsed, DLA or DUA are also going to be pulsed very soon after.
 

MikeMl

Well-Known Member
Most Helpful Member
In order to suggest something, I would have to know the voltages at DLS, DUS, DLA, DUA and the respective currents being switched? Is the minus supply terminal of the 555 logic tied to the ground reference of DLS, DUS, DLA, DUA?
 
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peterfares

New Member
DLS, DUS, DLA, and DUA are all at 0 volts when off and car battery voltage when pulsed.
DLS is door lock switch, DUS or door unlock switch, DLA is door lock actuator, and DUA is door unlock actuator.
There is not really much current being switched, all I need them for is to tell when they are on and off so that the circuit can pulse (take to ground) the correct button on a keyfob at the way right side of the circuit. Instead of the battery at the right, I put a 3.3V voltage regulator in place.
Whenever DLS or DUS are pulsed, DLA and DUA WILL be pulsed but DLA and DUA can be pulsed without DLS and DUS being pulsed.

When DLS and DUS are held to ground and either DLA or DUA are pulsed, the correct button on the fob at the right is pulsed, so the two 555s on the right are working correctly.
 
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MikeMl

Well-Known Member
Most Helpful Member
If DLA an DUA are the acutators, then it will take a current pulse of several AMPS!!!! to actuate them. The other end of the actuators are grounded to the car body, right?

If so, you will need PNP transistors, or PFETs, (high side switch) and the signal from the 555 will have to swing from gnd to 12V. I think a DPDT relay between the 555 and the signals is the simplest way to go.
 
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MikeMl

Well-Known Member
Most Helpful Member
No, I am not actuating them with this circuit, the circuit only needs to know when they are actuated (from the car).

Huh? Aren't you trying to interrupt the DLS to DUS connection?
 

peterfares

New Member
Basically this is what the circuit needs to do:
If DLA is pulsed
  • pulse the Fob Arm Button after 1 second
    • Except if DLS was pulsed up to 5 seconds before DLA
If DUA is pulsed
  • pulse the Fob Disarm Button after 1 second
    • Except if DUS was pulsed up to 5 seconds before DUA

Whenver DLA or DUA are pulsed
  • Break the connection between ARMPin and a remote starter
  • Break the connection between DISARMPin and a remote starter
 
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