Line powered audio switch, getting there it seems

Hi all

A few days ago, I started a thread to ask if it would be feasible to create a line powered audio switch connecting one stereo output to either of two inputs. After a nice discussion with many people, I came up with a schematic that is available at this address:

Along with it is the detail the working principle, as I understand it. Could anyone be kind enough to have a look at this and comment on it? I would very much appreciate feedback from more experienced designers.

Cheers Olivier

Nice try, but..................

OP213 3mA per opamp Iq.

consider the initial startup, no VCC.

Audio in via 100K resistor, how does the opamp rectify without VCC.

Keep trying...( I like the page design)

martin

After the first death, there is no other. (Dylan Thomas)

This might be a dead end, but

follow the transformer bridge rectifier If (a big IF) you can obtain 20uA you could power a 74HC4052 cmos switch. (Icc 18uA max)

martin

After the first death, there is no other. (Dylan Thomas)

I read in sci.electronics.design that OBones wrote (in ) about 'Line powered audio switch, getting there it seems', on Tue, 26 Apr 2005:

I don't think it will start, because the op-amp needs Vcc before it will generate it. You need to take your Vcc directly from the transformer secondary via a single Schottky diode and filter cap.

I read in sci.electronics.design that OBones wrote (in ) about 'Line powered audio switch, getting there it seems', on Tue, 26 Apr 2005:

Yes. First get your Vcc sorted out, then go on to the relay supply rectifier etc.

Doesn't the relay driver circuitry seem overly complicated? Why is an H bridge required? The relay has only 2 states, either operated or non operated. That takes only one transistor and simple toggle logic IMO.

As I said on the website, I know those buttons exist, but for the fun of it I'm investigating an electronics based solution.

Yeah, that's what I thought as well. But I think the schema I got for the op amp rectifier is wrong, there is an almost direct path from the transformer to the output.

Anyway, if I was to use a single low drop out diode (like BAT42 for instance), that would do half wave regulation and I guess it would be enough for my purposes. It would mean longer charge time, but that's no big deal. Would that be right?

Cheers Olivier

Thanks for the input, I'll keep trying. As to the page design, I like it too ;-)

Cheers Olivier

You have a basic problem with the law of conservation of energy. ;-)

Graham

This is a latching relay, with one coil. Depending on the current flow direction, the relay will be set or reset. Hence the need to have a circuit allowing to control which way the current flows inside the coil, and the H bridge is the only one I know of.

Nope, it's an Over Unity device, the palladium contacts on the relay will.......

martin

After the first death, there is no other. (Dylan Thomas)

Apart from the other problems already mentioned, you need to have some contact debounce, when the switch initialy makes contact the contacts bounce and make and break several times over about 10ms, wich wil togle the flip flop an inderterminate amount of times, an rc filter folowed by a schmit triger usualy sufices, or if you have make and break or changover contacts you can just use a capacitor.

Colin =^.^=

Could you explain a bit more, I'm curious.

Thanks for that.

The OP213 still draw 3 mA/amplifier. That corresponds to a 6 V drop across R4...

I don't think the opamp full-wave rectifier works like you think it does; it will never output a voltage greater than Vcc, and is therefore not helping anything. You can get rid of it.

Would a lithium battery be considered unsporting?

Jonathan

Basically says - you can't create more energy by use of a device than you had to begin with. All systems are 'lossy'.

Graham

Okay, I think I've got it sorted, it's online here:

It looks like following a trail of clues, but I'd like to eventually get there. Thanks to all for the help and support.

Cheers Olivier

Look Here !

You reckon you can draw 1mW from the audio line. Your loony 'active rectifier' will *consume* more power than that - even if it worked - which it won't

Nor is 1 mW capable of driving a relay.

Get real !

Bye bye......

Graham