Eletronic Switch !

[-_nando-_]

Hi !

I'm searching for an eletronic switch that works like a "relay". When have applied signal (5v or any other voltage) it closes the switch, and when the command signal is not present, the switch opens.

I tried the CD4066, and it works. The closed resistence is perfectly ok (120Ohms), but it's opened resistence is 34k, that isn't low enough.

If the closed resistence is something about 1k or less it will work perfectly, but the open resistence must be as higher as possible, something about 1Mohm would be perfect.

Any other suggestion? I'm making a project, and I need 48 eletronic switchs, and it would be very expensive if I use 48 relays...



Best Regards !

[cpemma]

Originally posted by -_nando-_
... but it's opened resistence is 34k, that isn't low enough.

I'm surprised you're finding it so low, the datasheet's quoting 1uA max leakage current, but you could check analogue switches such as the DG418DJ. They're of use where a much lower on resistance is handy (or higher voltage handling), but leakage current is <1nA according to the d/sheet.

[I_Forgot]

What are you trying to switch? AC power? Small signals? DC power?
How much current? What voltage?

I_F

[AndrewT]

Hi,
would discrete use up too much PCB space?

[-_nando-_]

Well, this switch seems to work fine, but they are more expensive than a little relay, so it's out.

I have 4 instruments channels, and 6 sound efects shared.

So, the sound effects output are conected directly to the amplifier, through resistor and a buffer. The six sound effects outputs have 2k2 resistors, that are conected to one buffer, so to choose the desired sound effect, we must switch a sound channel to an effect input, making any combination.

As the sound effects input are also buffered (high input impedance), if the switch off state have a relatively "low" resistance (like 34k), it still conecting the channel to the effect, and high distortion appears when the switch is off. As the channels are buffered too, I placed a 1k resistor to the ground on the effect input, to eliminate the switch off state noise, but as it's resistance is 34k, I just divided it 34:1, and still a very perceivable noise. That's why a relay would work perfectly, because it's off state have infinite inpedance.

An eletronic switch that its off state is 1M or higher would work perfect, but it must be cheaper than little relays.

AndrewT, there's no problem at all about use discretes, do you think that it would work for me? What I need is a not so low impedance on state (1k is more than enough), and a very high impedance off state.

[cpemma]

Originally posted by -_nando-_
I have 4 instruments channels, and 6 sound effects shared...

This system is really designed for switching several channels at once, such as video signals, but it may provide food for thought.

There are ICs designed for switching audio inputs, found in most remote-operated equipment; though comparative expense may put you off. TDA 1029 is one, 4 stereo inputs to 1 pair of outputs.

[-_nando-_]

Very nice article !

I need something exactly like the CBT3244, but with one control (enable/disable the switch) for each IO pair.

The CBT3244 have eight IO pairs, but only 2 controls, so control 1 will enable 4IO pairs at the same time and the control 2 will enable the other 4IO pairs in the same way.

I could use it, but as it would work only like two relays, it would be cheaper than tinny relays only if I buy it in quantity of 1000

[Magura]

Originally posted by AndrewT
Hi,
would discrete use up too much PCB space?

I would like to hear your take on making discrete solid state relays.

Magura

[-_nando-_]

CBT3125 ! Take a look. It's just like CBT3244 (from the tutorial), but with 4 IO pairs with one control (OE) for each IO pair !

The switcher is the same family of the article's switch, do you think that it really will work for me? It must have a high off impedance.

[Boris_The_Blade]

well, not really...but the inputs on most analog switches do not tolerate negative voltages real well...they will distort and/or short the signal. make sure to bias them halfway between the positive supply and decouple the input and output with a capacitor suited to your low frequency desire.

Analog devices makes dual supply analog switches (like the ADG222, but there are others) that are suited better to audio signals. Some parts spec the THD, so you might want to look at that also for audio quality.