Excuse my ignorance, but can you elaborate just a little?

 

I feel that it may be pertinent to say that the current in the "off" state should be very low in the entire circuit as it will be an application that is in a vehicle and battery drain would be an issue if the vehicle is not being used often.

Does the circuit need to operate with the ignition switch off?

 

I feel that it may be pertinent to say that the current in the "off" state should be very low in the entire circuit as it will be an application that is in a vehicle and battery drain would be an issue if the vehicle is not being used often.

Then use the CD4538 chip that @shortbus recommended. Draws micro-amps in the off state.

 

Basically, I would have 12v constant applied to the circuit at all times and the trigger will be the unlock signal that is received from the door lock control box. It is a 12v pulse. It is not long enough to activate the accessory I want to activate, hence the need for this circuit that will activate with a quick pulse for about 10 seconds to allow enough time for the accessory to start up and then everything can be controlled from that accessory once it starts.

Yes, it would activate without IGN on. I've got all the wiring on the vehicle, that's super easy. It is this small component to the system that's thrown me for a little loop.

 

A CMOS 555 chip will also draw only low power - here is a circuit that should fill your needs. Just get rid of the 12V and momentary switch. Connect your 12V trigger directly to the 1k resistor on the base of the transistor. The 100k on the base of the transistor is optional. Use a 2N3904 or 2N2222A transistor or almost any other NPN transistor.

 

Here is the simulation for your enjoyment. The bottom blue trace is the base-emitter voltage of the NPN when a 12V signal is applied to the transistor connected to the base (I made a mistake in the schematic above - that should be a 33k to 100k transistor, not a 1k. Everything else looks fine to me.

 

Thank you very much!!! What software are you using?

 

Thank you very much!!! What software are you using?

iCircuit for iPad.

It has some glitches on 555 timer retriggering but it works alright otherwise.

 

I've got an application where I want to take a 12v input signal to latch a 12v for just 10 seconds and then to stop and have the circuit open again until the input signal is received. I just need roughly 12v output. Really, input could be 11-15v and output can be a large range of voltage as well.

What would be the best way to go about this?

Thanks for any assistance, it is greatly appreciated.

If precision is not important - you could just charge a capacitor and let it discharge through a relay coil - some older motorcycle indicator relays are that simple.

 

How would you recommend activating the discharge of the cap?

 

Any recommendations for PC/Mac based circuit design and PCB software. It's fine if it is paid, doesn't have to be free or web based.

 

Any recommendations for PC/Mac based circuit design and PCB software. It's fine if it is paid, doesn't have to be free or web based.

iCircuit for windows.

 

How would you recommend activating the discharge of the cap?

You can charge the cap via a resistor that's too high to supply the relay coil on its own.

An SCR or the 2 transistor equivalent can latch so the cap discharges the coil, when the current falls below the holding value it unlatches by itself.

The 2 transistor SCR equivalent is easy to rig for a trip point voltage, so the whole thing can be automatic.

 

Below is my take on a simple two transistor circuit that should do what you want, if you don't want to use a 555.
The transistors can be just about any small NPN and P-MOSFET devices.
You can change the value of R1 to adjust the pulse time or use a 100k pot for R1 if you want it to be adjustable.
It draws only a small leakage current when not energized.

 

Interesting. I'll probably give the 555 timer circuit a shot and see how that goes.

Any recommendations on a large electronics component LOT that is out there. I've been searching around, but haven't found anything too great or that isn't way overpriced. Need to get a good base of components here so I'm not always ordering a few at a time, "nickel and diming" me to death.

 

Interesting. I'll probably give the 555 timer circuit a shot and see how that goes.

Any recommendations on a large electronics component LOT that is out there. I've been searching around, but haven't found anything too great or that isn't way overpriced. Need to get a good base of components here so I'm not always ordering a few at a time, "nickel and diming" me to death.

I use Digikey.com and select 1st class US mail (if you are in the US). Shipping is about $3 on small lots of small pieces. About 6 or 8 if they can't fit every thing in an envelope.

 

I'm going to get some parts ordered up for the circuit GohperT supplied. It will at least get me going with something. Thanks again for all the help. I'm sure I'll have some questions and will post up on how it goes!! I'll measure the current on it when it is not in operation and just supplied with the constant 12v.

 

@live4soccer7

Order the LMC555CN. It has very low current draw in the off state.

 

I was heading toward a solution like Wally's, but he beat me to it. Since I have a biological compulsion to present alternatives to the 555, here is one using a classic monostable circuit. It looks like a lot of parts, but five of them (D1, D2, D3, R2, R3) are there to protect the circuit from its environment and itself. For example, D3 is a combination automatic capacitor discharger and U1C input undervoltage/overcurrent protector. Note: There is no need for 1% resistors or that specific MOSFET. These are the parts in my CAD library.

Variations:
1. For a negative-going input pulse, disconnect pin 13 from pin 3 and connect it to pin 4.
2. For a negative-going output that pulls a load to GND, connect the gate of an N-channel power MOSFET to U1 pin 11.

ak

 

Interesting. Is this the IC you are referring to:
http://www.futurlec.com/4000Series/CD4093.shtml

Mofset:
http://www.vishay.com/docs/91278/sihfr902.pdf

Any advantages to this vs the 555?