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12v Sensing Switch

Hi guys,

I asked this question a long time ago, and I only got back to finishing the project recently. My problem was that I needed to create a circuit that turned another on or off, depending on the voltage state of a given wire, 12/6v.

So, I came up with the following,

12V + o----. | | Relay _|_ - 1N4001 Coil |_/_| ^ | | o----' ___ |/ JOE ---| Zener .-. | | | | 10K| | | '-' | | | o----' | === GND

Which works absolutely perfect (ish). It works fine, but when I installed this into my car, the 12v/6v wire that is meant to trigger the circuit has 0A running through it - it is more a clock pulse thing I think. So, how can I make a circuit that will trigger the above circuit given two states,

12v Circuit Off 6v Circuit On

Given a wire that can be in two states, 12v 0A and 6v 0A. I'm thinking I might have to use a Zener to reduce the voltages to 6v\\0v and then some kind of IC like a 555 which the clock input to switch a J-K, or something along those lines.

Help is very appriciated and the simpler the better!

Thanks guys, Ben

Reply to
lessani
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I have found this,

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It looks like the perfect solution to my problem, what do you think?

Reply to
lessani

Hi, Ben. You can get a "12V = OFF, 6V = ON" by using a PNP transistor, like this (view in fixed font or M$ Notepad):

| | +12V +12V | | | | .-. | | R2| | | | | | | | '-' | |Vin ___ | |< | o-|___|- -| | R1 |\\ | | | .---o | | | | 1N4001 C| | - C|RY1 | ^ C| | | | | | | | === === | GND GND (created by AACircuit v1.28.6 beta 04/19/05

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If you use a PNP darlington, you can drive a decent-sized relay with R1 = R2 = 10K. The relay turns on when the input voltage goes down to 6V, drawing half a milliamp of current from the base of the PNP.

If you want to interface with some digital logic, just use a standard PNP like a 2N3906, and use a 1K load resistor instead of the relay and the diode. You will then have a logic signal you can interface to CMOS logic (you can't use this with TTL) -- a logic "1" (12V) at the collector when the input is 6V, and a logic "0" (GND) when the input is

12V. 4000-series logic will work with your 12V supply, which should make things easier.

I'm not clear on what you're trying to accomplish with this signal. You need to carefully define what you need to do.

Good luck Chris

Reply to
Chris

Let me re-state what I think you want:

You want the relay to be energized when a

6 volt pulse occurs, and to stay energized until a 12 volt pulse is detected. The relay will then stay de-energized until a 6 volt pulse occurs again.

Is that correct?

If so, and if your pulse is at least 10 mS long, you can do it with 2 relays and a couple of parts.

N/O (6v relay)

+12 --------. +-------------------.--- | | ^---+ ||--------------------------+ [R1] | | | +->|-+ | | | +----+ +----+---+ | | 12V | | | 6V | | Relay _|_ - | Relay _|_ - 1N4001 Coil |_/_| ^ [C1] Coil |_/_| ^ | | |100uF | | | | | | | Gnd --------+----+---+---------------+----+

R1 is chosen to be equal to the coil resistance of the

6V relay. You can take +12 output from the open point of the 6V relay when the relay is energized - or you can use a double pole relay and take the ouput from the second set of points.

Ed

Reply to
ehsjr

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