LM4780, mute + microcontroller

edpgc · 16th August 2004, 06:26 PM

Hi all

I've got a LM4780 amp running pretty nice, thanks to some helpful hints from you guys. Now I want to switch the mute on and off from a microcontroller, and this is causing me great confusion. I thought I had it sorted with a npn and pnp transistor tied together, it worked in my head but not in the real world apparently.

Anyone done anything like this before? The output is 0/3.3v, 3.3v can be on or off doesnt matter, but I need to switch the mute resistor on and off, ie connect it and disconnect it from vee (about -30V)

Just need to know how to connect it all together, I'm sure I'm close, I don't want to have to use a relay or something silly like that for this!

Cheers guys!

Ed

Faber · 16th August 2004, 07:56 PM

You didn't tell us which MC are you using, but you can use something like this, using the 16f86 microchip.

Sibstitute the led with a transistor and you're done.
bye!

edpgc · 16th August 2004, 08:42 PM

just a pic, can do about 20mA I think

Now which LED?! Or am I being thick?

johnnyx · 16th August 2004, 09:38 PM

What about using an opto - coupler?
The input or driving side is driven like a led, the output side could be a transistor or fet or thyristor,,,,, there are many types. With the isolation this method gives you, there will be no problem with the -30v rail. It will interface easily with a microcontroller.

edpgc · 16th August 2004, 09:40 PM

Interseting idea, really looking for a solution just using parts I've already got. THis really shouldnt be difficult, perhaps I should sleep on it!

carlosfm · 17th August 2004, 01:14 AM

10k resistor from the Mute pins to V- : sound.
Direct connection from the Mute pins to ground: no sound.

I would do it with a simple switch.

Why a microcontroller?

theChris · 17th August 2004, 01:48 AM

with a microcontroller, you could make an IR sensor turn on, or signal sense turn on, or ect. possibly so you can control the amp from a computer?

Faber · 17th August 2004, 08:19 AM

Quote:

Originally posted by edpgc
just a pic, can do about 20mA I think

Now which LED?! Or am I being thick?

Oooops, wrong image. anyway, you just need 1 mA for both channels, it's quite simple to achieve with the image I've attached. The MC have to drive a transistor, the trans opens up and the current flows as in the picture I've attached.

The intended picture of my previous post is the following.
Bye!!

Faber · 17th August 2004, 08:20 AM

picture

edpgc · 17th August 2004, 04:25 PM

but that won't work, the emitter will be at -30v, and the switching voltage is 0 / +3.3 result is that the transisotr is always fully suturated, whether its at 0 or 3.3, since they are both much higher voltage than the -30v of vee attached to the transistor.

Thanks

Ed

16th August 2004, 06:26 PM	#1
edpgc diyAudio Member Join Date: Apr 2004 Location: Birmingham, UK	LM4780, mute + microcontroller Hi all I've got a LM4780 amp running pretty nice, thanks to some helpful hints from you guys. Now I want to switch the mute on and off from a microcontroller, and this is causing me great confusion. I thought I had it sorted with a npn and pnp transistor tied together, it worked in my head but not in the real world apparently. Anyone done anything like this before? The output is 0/3.3v, 3.3v can be on or off doesnt matter, but I need to switch the mute resistor on and off, ie connect it and disconnect it from vee (about -30V) Just need to know how to connect it all together, I'm sure I'm close, I don't want to have to use a relay or something silly like that for this! Cheers guys! Ed

17th August 2004, 01:14 AM	#6
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Mute on the LM4780 10k resistor from the Mute pins to V- : sound. Direct connection from the Mute pins to ground: no sound. I would do it with a simple switch. Why a microcontroller?

17th August 2004, 01:48 AM	#7
theChris diyAudio Member Join Date: Dec 2001 Location: SIUE, Illinois, USA	with a microcontroller, you could make an IR sensor turn on, or signal sense turn on, or ect. possibly so you can control the amp from a computer? __________________ if only it could be used for good, not evil...

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16th August 2004, 08:42 PM	#3
edpgc diyAudio Member Join Date: Apr 2004 Location: Birmingham, UK	just a pic, can do about 20mA I think Now which LED?! Or am I being thick?

16th August 2004, 09:38 PM	#4
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	What about using an opto - coupler? The input or driving side is driven like a led, the output side could be a transistor or fet or thyristor,,,,, there are many types. With the isolation this method gives you, there will be no problem with the -30v rail. It will interface easily with a microcontroller.

16th August 2004, 09:40 PM	#5
edpgc diyAudio Member Join Date: Apr 2004 Location: Birmingham, UK	Interseting idea, really looking for a solution just using parts I've already got. THis really shouldnt be difficult, perhaps I should sleep on it!

17th August 2004, 04:25 PM	#10
edpgc diyAudio Member Join Date: Apr 2004 Location: Birmingham, UK	but that won't work, the emitter will be at -30v, and the switching voltage is 0 / +3.3 result is that the transisotr is always fully suturated, whether its at 0 or 3.3, since they are both much higher voltage than the -30v of vee attached to the transistor. Thanks Ed

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