Solid State Switch

[tntero]

Hello there, im taking an electronics course, but because im on vacation from school, i cant contact my teachers to help me with this one, so here goes:

I play guitar, and i like building effects pedals, so a few time ago i had an idea to do an electronic 555 based auto killswitch, basically, the 555 will send pulses that open and close a switch, my doubt is what to use as the switch. i first thought of a transistor, but the emitter has to be connected to ground, and i only want it either to let the input go to the output or open the switch and cut the signal.

I dont know if you understand what i mean, if you need help understanding the project, just say.

Thanks in Advance
Antero Duarte

 

[crutschow]

Is this an audio signal you want to switch?

 

[tntero]

yes exactly, it will act the same way as a mechanical relay, when i give it an impulse on the gate, it should close the switch, so the audio signal passes, do you know what i mean? my problem is, for example with a transistor, i cant have a signal on the colector that will connect to ground when i have power on the gate.
I've been researching, and i've seen a couple of things online about Mosfet Switching, but i couldnt understand, im portuguese, so its kinda hard for me to understand the technical stuff out there in english xD

 

[shortbus=]

You need something that is called a 'make before break' switch. If you don't use this type of switch, there will be a 'POP' from the amp when switching. Think about when you pull out the cord from the guitar when the amp is on. Here is a link to some of the switches that will work; https://www.electro-tech-online.com/custompdfs/2011/07/MAX4624-MAX4625.pdf

 

[tntero]

You need something that is called a 'make before break' switch. If you don't use this type of switch, there will be a 'POP' from the amp when switching. Think about when you pull out the cord from the guitar when the amp is on. Here is a link to some of the switches that will work; https://www.electro-tech-online.com/custompdfs/2011/07/MAX4624-MAX4625-1.pdf

That seems like exactly what i want, so i just need to connect that to the Vout of the 555 and it will do the kill-switch, correct?

 

[crutschow]

Be aware that those switches, if operated from a single supply voltage, can only switch signals between 0V and the supply voltage. Thus to switch audio signals that go above and below ground, you will need to couple the signal through capacitors at the input and output of the switch, and offset the signal with two equal value resistors connected as a voltage divider between ground, the switch input (after the cap) and the supply voltage.

 

[tntero]

Be aware that those switches, if operated from a single supply voltage, can only switch signals between 0V and the supply voltage. Thus to switch audio signals that go above and below ground, you will need to couple the signal through capacitors at the input and output of the switch, and offset the signal with two equal value resistors connected as a voltage divider between ground, the switch input (after the cap) and the supply voltage.

sorry i got lost in the middle, is there any way you could give me a schematic?

 

[crutschow]

Here's an example circuit.

 

[shortbus=]

Be aware that those switches, if operated from a single supply voltage, can only switch signals between 0V and the supply voltage. Thus to switch audio signals that go above and below ground, you will need to couple the signal through capacitors at the input and output of the switch, and offset the signal with two equal value resistors connected as a voltage divider between ground, the switch input (after the cap) and the supply voltage.

Huh? These are bilateral audio switches, made for this type of use. To my knowledge the internal part of the switch is not dependent on the supply busses of the IC.

 

[crutschow]

Huh? These are bilateral audio switches, made for this type of use. To my knowledge the internal part of the switch is not dependent on the supply busses of the IC.

Well, if you show me a bilateral switch that will transmit audio signals that go above or below the supply voltages (or below ground if it is powered by a single supply), then I'll retract my statement.

 

[Sceadwian]

shortbus, try actually reading the PDF, it specifically states that analog signals from V+ to GND are passed, it can not pass beyond the rails.

 

[shortbus=]

So then they are digital switches and not analog? Why are they being marketed as analog then?

So for the OP this would be a better choice; https://www.electro-tech-online.com/custompdfs/2011/07/MAX4744-MAX4746H.pdf

 

[crutschow]

So then they are digital switches and not analog? Why are they being marketed as analog then?

So for the OP this would be a better choice; https://www.electro-tech-online.com/custompdfs/2011/07/MAX4744-MAX4746H-1.pdf

They are analog switches (that is they can carry analog signals). They just don't go below the minus rail voltage.

But the Maxim device you referenced does go below ground, so I hereby change my statement to "most solid-state analog switches cannot carry signals below the negative rail". But obviously some do.

 

[shortbus=]

@crutschow - Maxim makes a bunch of different ones; **broken link removed**

I learn some thing here, I was thinking that analog meant that the signal went between + and - voltage, like a sine wave or an audio signal. Didn't know it also could be just between +volts and common/ground.