Simple switching/pulse project

[dbtoutfit]

Hi,

I am looking for help on making a simple switching/pulse project.

This device needs to work of 12v dc.

Right now I have relays doing the switching but I have many catch 22's with this and I am thinking a IC 555 timer maybe needed here.

Basically what I need is a setup where when 12v dc is applied a pulse is sent to "short" a power button. At this time I have done this by using a 12v relay with a 5v relay. When I apply 12v to the device it trips the relay and shorts the connection after that the device I am turning on supplies 5v to a 5v relay that releases the 12v relay so that the 12v relay will not hold the "short" to the switch as I need a simple "quick" pulse to complete the switch circuit.

This device simply replaces the need to press the momentary button manually.

The 1st problem with my current setup is that I also need it to "short" the switch when 12v is disconnected from the device.

The 2nd problem I am having is when 12v is applied I need the pulse to be delayed, say for 5seconds (A variable pod would be great so that the delay timing could be adjusted from 1-15 or maybe up to 30 seconds)

**broken link removed**

 

[ljcox]

Here is a suggestion for you.

Circuit description.
At switch on, C2 charges rapidly to just under 12 Volt.

C1 charges slowly via R1. When it charges to the upper threshold of IC1a, X goes low & Z goes high. (the USB is at 0 Volt, so A is high)

Q2 turns on and operates K1.

When the USB voltage rises, Q1 turns on & A goes low, X goes High, Z goes low, Q2 turns off & so K1 releases.

When the 12 Volt is switched off (D1 blocks the charge on C2 from the 12V line), B goes high, Y goes low (since C2 is still charged), Z goes high Q2 turns on and operates K1.

Note that C1 discharges rapidly via D3 and R4 (I assume that the 12 Volt drops to zero rapidly)

C2 discharges via the coil of K1 and so K1 releases after a brief delay and the circuit returns to the initial state.

Z1 is to protect the gate of Q1 from electrostatic discharges on the USB line (if the line is open during testing, you may accidentally apply an electrostatic discharge onto the USB line)

IC1 is a Quad Schmitt Trigger NAND gate package CD4093 or similar.

 

[dbtoutfit]

Thanks Len

Any way to squeeze a variable pod in to be able to adjust the time?

See when I crank my car the dc-dc converter is not supplying enough power to the laptop while the car battery is under crank load. Yet there’s enough power for the switch/pulse to be sent thus the laptop doesn’t see it. I need to be able to delay it and adjust the delay.

So I crank the car 12v is sent to the switch and the timer kicks in and counts down to X amount of time adjusted by a pod and then pulse is sent.

Or am I missing something on your schematics that already accomplishes this?

Thanks
Eric

 

[ljcox]

Thanks Len

Any way to squeeze a variable pod in to be able to adjust the time?

R1 & C1 provide a delay. If R1 = 1M, then the approximate delay is = C1 in uF, eg. if C1 = 4.7 uF, then the delay will be somewhere in the 3 ~ 6 second range. Altenartively, if you make R1 = 10M, then 0.47 uF will give you the same delay.

See when I crank my car the dc-dc converter is not supplying enough power to the laptop while the car battery is under crank load. Yet there’s enough power for the switch/pulse to be sent thus the laptop doesn’t see it. I need to be able to delay it and adjust the delay.

So I crank the car 12v is sent to the switch and the timer kicks in and counts down to X amount of time adjusted by a pod and then pulse is sent.

Or am I missing something on your schematics that already accomplishes this?

Thanks
Eric

Eric,
Now that I know that it is to be in a car, I'll have to make a few changes.

But I suggest you learn how this one works before I do that.

I'll send you an email.

 

[ljcox]

Here are 2 more options for you.

 

[dbtoutfit]

emailed you