Evaluate my control board, pretty please?

[Otomaru]

Hello.

This is my first circuit ever. I have pretty basic knowledge and pretty much 0 experience.

I'm making a circuit which goal is:

• Turn on AMP when my PC turns on.
• Don't turn it back on if i turn it off.
• Turn off as my PC turns off.
• Circuit is not working if PC is off.

It takes 5v from USB from PC side. 2v signal from AMP when it's on. And for power I'm connecting to AMP's starter board, which outputs 12v when off, 16 when on. Relay shorts the on/off button on AMP.
Please validate my circuit - what can be done better, what safety measures i miss? I don't want to burn either of my devices.
Also it would be great if you could recommend a better OP-AMP and voltage regulator. Maybe you know the perfect transistor as well.

Circuit in attachment.

[sanwal209]

Hello,

You made it really complex and its over kill. You can do this with only a single relay. Why dont you turn on the relay with USB 5V and relay turns on the amp. Check the attached image.

So when there will be 5V the amp will be ON and when you turn off PC amp will be off.

[Mechatrommer]

its difficult to follow your circuit, whats the K in circle (1mH) and capacitor (1ohm) next to it? whats AMP_SIGNAL_ON, whats AMP_PSU? but what i understand is, you are burdening the 5V rail with 5ohm divider R8 and R7, thats 1A already, try 4Kohm and 1Kohm. and you will damage Q2, if PC_USB is 5V from PC USB, put limiting resistor to the base.

[Otomaru]

You made it really complex and its over kill. You can do this with only a single relay. Why dont you turn on the relay with USB 5V and relay turns on the amp. Check the attached image.

So when there will be 5V the amp will be ON and when you turn off PC amp will be off.

There is only one relay. It's a screenshor from application i use, i don't know why it has drawings like that for some things, but the relay is the parralel to zender diode.
USB has no power when PC is off. So i'm powering the relay from AMP. I'd like to use basic components to get some experience with them.

its difficult to follow your circuit, whats the K in circle (1mH) and capacitor (1ohm) next to it?

That would be the relay with 1mh coil that has 1ohm resistance. Ignore those values. Again, i don't know why this application draws it like that.

whats AMP_SIGNAL_ON, whats AMP_PSU?

Those are probes for graphs. AMP_SIGNAL_ON would be 2v signal i get from it when it's on, 0v when off. AMP_PSU is likewise probe for graphs, from starter board (Board that powers standby phase and turns on the big transformer when the device is on) 12v when off, 16v when on.

ut what i understand is, you are burdening the 5V rail with 5ohm divider R8 and R7, thats 1A already, try 4Kohm and 1Kohm

Yep, kinda forgot the ohms law there. Will fix that.

and you will damage Q2, if PC_USB is 5V from PC USB, put limiting resistor to the base.

Roger. Can any one explain why that's damaging? Also should i do something to protect signals from USB and AMP_ON?

[sokoloff]

You made it really complex and its over kill. You can do this with only a single relay. Why dont you turn on the relay with USB 5V and relay turns on the amp. Check the attached image.

So when there will be 5V the amp will be ON and when you turn off PC amp will be off.

USB has no power when PC is off. So i'm powering the relay from AMP.

That's sanwal's point: the USB has no power when the PC is off, so then the relay switches off and cuts the power to the amp. Then, when the PC turns on, USB gets 5V, switches the relay, turning on power to the amp. Put a diode to protect the USB from the relay transients and the project is all done. The relay doesn't need power from the amp; it needs a control signal from the PC (over USB, the presence of USB power is enough in your case) and needs mains power which it will switch to the amp when the PC turns on.

I'd like to use basic components to get some experience with them.

There's nothing wrong with that per-se, but when it gets in the way of accomplishing the project's functional goals, you have to decide whether you want the project to work or to learn. Both have value.

[Otomaru]

That's sanwal's point: the USB has no power when the PC is off, so then the relay switches off and cuts the power to the amp. Then, when the PC turns on, USB gets 5V, switches the relay, turning on power to the amp.

Relay shorts the on/off button on AMP.

It mimics button press, it's not a switch for AMP power. So i need pulses at the right moments. I understand i can do the signal handling and relay control with microcontroller, though i'd like to avoid it for this project. I have other projects in mind where a microcontroller is a must.

I'd like to use basic components to get some experience with them.

There's nothing wrong with that per-se, but when it gets in the way of accomplishing the project's functional goals, you have to decide whether you want the project to work or to learn. Both have value.

How can there be anything wrong with that for a individual on his personal time and resources? How is it getting in the way? Is that a projection? Why not both?
The functional circuit is already done, there is no need for a microcontroller any more. I'm here to know if there are fatal flaws in it that would damage either my AMP, PC or the circuit itself - Like what Mechatrommer pointed out.

[Rerouter]

If your simulating a button press when on, and a button press when off, interlocked by the amps current power state, that is not that hard,

Your going to need 2 inputs, one being the 5V usb supply, and the other being some power rail or node in the amplifier that changes with the power state, e.g. the LED,

You monitoring for 2 conditions, and both of these should press the button in effect,
1. USB line goes high (5V)
2. USB line goes low (0V)

a nice easy logic level,

Then you have your 4 interlocked states
1. USB goes high and amp is on : do nothing
2. USB goes low and amp is off: do nothing
3. USB is on and amp is switch off: do nothing
4. USB is off and amp is switched on: do nothing


what we have here is a single XOR logic gate truth table with the state only being checked after the usb input changes state.
so first to tackle the only when usb changes side, this is an XOR gate with a RC delay on 1 input, it will only output a 1 when the state changes, you AND this with the result of your first XOR (sadly you cannot make an AND gate from the spares in the first chip. I would imagine you would want to add a RC delay on this first XOR's input, so it doesn't respond to a transient on the usb side, but say 1-2 seconds of a constant state,

you would then want a 1 shot circuit to trip the relay on for a specific amount of time and no more, as it will likely do a hard reset if you hold the power button for 7+ seconds

so 2 xor gates, and 1 and gate should accomplish what your after.

edit: rethought through the corner cases.

[Otomaru]

@Rerouter - Did you even look at the circuit? What are you doing?

Why is Mechatrommer the only one who seams to pay atention...

Here's the breakdown of the circuit logic:

• R1 C1 creates the delay for "ON" pulse, when this RC reaches saturation for Q1, Q1 creates SC to ground cuting the USB input signal further thus creating pulse as SWITCH_ON_SIGNAL
• When AMP is on i have 2 volts coming from where i have AMP_SIGNAL_ON probe, that's my "OFF" signal but i want to silence it when USB has power, so Q2 runs it to ground while USB is on.
• Now i join both of these signals as SWITCH_SIGNAL for relay.
• To enable these signals to be interpreted by U3A only when the PC is on and shortly after it's off, i have R2 C2, that's the "WORK ONLY WHILE" signal which is interpreted by COMPARATOR OP-AMP U2A which powers U3A only when needed.
• So now U3A works only when needed and sends (filtered) signal further to relay circuit (R4, Q3, D1, K1).
• And now the relay behaves as i wanted.

But i came here to validate for electrical errors, not logical.

[sokoloff]

@Rerouter - Did you even look at the circuit? What are you doing?

Why is Mechatrommer the only one who seams to pay atention...

Can't speak for @Rerouter, but I can say that my first impression was "[Fellow] beginner comes in asking for a fairly simple set of requirements and attaches a relatively complicated circuit." and "Amplifier is typically a power-cycled device [hard power cut] where a receiver is typically controlled with a button press [soft power]" and "When I was an even more beginner than now, I came up with all kinds of over-complicated solutions."

Relay shorts the on/off button on AMP.

It mimics button press, it's not a switch for AMP power. So i need pulses at the right moments.

Aha... Your requirement in your first post was "Turn Amp on when PC turns on". If it's like the amp that drives my subwoofers in my home theater, that screams "control mains power" not "simulate the press of the soft power button", so that's the solution path I went down (and I presume same as @Rerouter).

Among those things, it's easy to see how I (and I think Rerouter) concluded that you seemed to be making a technical mountain out of a molehill.

Now that we know you have a receiver that you want to control, I would consider a solution like this:

1. See if it can be set to "power on after power loss". If so, and you never want to use it with the PC off, just use a relay to switch the mains and you get 100% of the functionality you listed. Relay to power it up, amp turns on after power loss. Turn it off manually, it stays off. PC powers down, amp has power cut.

2. If it does not support "turn on after power loss", and you never want to use the device with the PC off, still do as in #1, but also do one of:
2a. Program a simulated button press with a +5V supply from USB. I would look into whether a Reset Controller IC can accomplish what you want. TI's page on them, but there are many other vendors. These are neat little devices that take a lot of the grunge out of holding a reset line while a power supply stabilizes.
2b. As in 3 below.

3. If it does not support "turn on after power loss" and/or you want to use the device with the PC off some of the time, then look to see if the device has a discrete IR code for "power on". If so, make your device emit that IR code on power up and the IR code for power off on loss of power. (You can use a cap to store enough power to emit a final IR sequence after power loss.) This solution has the advantage of having no mains wiring and no work inside the audio device at all and just a small stick-on IR emitter.

The reason for the additional complexity in #3 is that if you are simulating a button press for "power toggle" with your device, then you can get out of sync with the device. (Device is already on; PC powers up, button press toggles the power off. I know this is what you're doing with the feedback circuit from the amp; I'm just wondering if there's a simpler way that involves no surgery on the audio device.)

If you do go looking in that database, note that "Power ON" is not always called that. It's sometimes called "Zone 1 ON", "Z1 ON", "Main Zone ON", etc. Also note that just because the device's remote doesn't have a discrete power on and power off button doesn't mean that the receiver won't understand such a code if sent it.

I know you said you aren't looking for logical help. If this response offends you by offering logical help, please ignore it and consider that I've authored it for other people who might look for similar solutions in the future. If you haven't considered using IR, I think it's worth considering.

I'd like to use basic components to get some experience with them.

There's nothing wrong with that per-se, but when it gets in the way of accomplishing the project's functional goals, you have to decide whether you want the project to work or to learn. Both have value.

How can there be anything wrong with that for a individual on his personal time and resources? How is it getting in the way? Is that a projection? Why not both?

There's nothing in the least bit wrong with it. I do that all the time (in fact, I'm doing it right now). The root of my response was a misunderstanding of what you were trying to do. On a beginner forum, that's common; sometimes it's the original poster, sometimes it's the responders, sometimes it's both. I misunderstood your original post (I believe this was a "both" case, but in any case, I misunderstood you). You replied to others with some rejection of their solution which seemed like perfectly reasonable solution to me and so I asked what your goal was. It wasn't meant to be accusatory at all; I sympathize with (and try to model for myself and my kids) having fun learning about electronics.

[Otomaru]

Can't speak for @Rerouter, but I can say that my first impression was "[Fellow] beginner comes in asking for a fairly simple set of requirements and attaches a relatively complicated circuit." and "Amplifier is typically a power-cycled device [hard power cut] where a receiver is typically controlled with a button press [soft power]"

Aha, my bad. Should have had been clearer with what I meant with AMP. My apologies. Why “receiver” though? English is not my native language and “receiver” instead of “amplifier” does not sit well with me. I mean the main function is to amplify signal to drive larger speakers. Does it come down to just how it’s powered?

1. See if it can be set to "power on after power loss". If so, and you never want to use it with the PC off, just use a relay to switch the mains and you get 100% of the functionality you listed. Relay to power it up, amp turns on after power loss. Turn it off manually, it stays off. PC powers down, amp has power cut.

Seams to be a option, but that way I’m losing some of receiver functionality.

3. If it does not support "turn on after power loss" and/or you want to use the device with the PC off some of the time, then look to see if the device has a discrete IR code for "power on". If so, make your device emit that IR code on power up and the IR code for power off on loss of power. (You can use a cap to store enough power to emit a final IR sequence after power loss.) This solution has the advantage of having no mains wiring and no work inside the audio device at all and just a small stick-on IR emitter.

That’s the plan for future with Arduino. That’ll be a lot more time consuming than this circuit I’ve designed.

The reason for the additional complexity in #3 is that if you are simulating a button press for "power toggle" with your device, then you can get out of sync with the device. (Device is already on; PC powers up, button press toggles the power off.

Missed that, not that important but I think I can fix it with another transistor.

I know this is what you're doing with the feedback circuit from the amp; I'm just wondering if there's a simpler way that involves no surgery on the audio device.)

Yea, that’s why I was looking for help to validate it’s safety.

I know you said you aren't looking for logical help. If this response offends you by offering logical help, please ignore it and consider that I've authored it for other people who might look for similar solutions in the future.

I’m no snowflake. My communication skills might be lacking and some times I lose patience. I didn’t come here to help me figure out how to achieve the functionality I listed is what I meant. Pointing out logical errors is welcome, you pointed out that my circuit will turn off the device when it’s already on and i turn the PC on, and I thank you for it. Mechatrommer pointed out what i was looking for and i thank him for it, I just want to know if there’s more I should do to protect circuits. ...and recommendations for voltage regulator, transistor and OP-AMP models.

If you haven't considered using IR, I think it's worth considering.

I have plans for whole room. I have considered IR and I already have the parts needed. I’ll change it in future, but now I want some practice with basic elements, transistors, chips like OP-AMP and prototype boards.

There's nothing in the least bit wrong with it. I do that all the time (in fact, I'm doing it right now). The root of my response was a misunderstanding of what you were trying to do. On a beginner forum, that's common; sometimes it's the original poster, sometimes it's the responders, sometimes it's both. I misunderstood your original post (I believe this was a "both" case, but in any case, I misunderstood you). You replied to others with some rejection of their solution which seemed like perfectly reasonable solution to me and so I asked what your goal was. It wasn't meant to be accusatory at all; I sympathize with (and try to model for myself and my kids) having fun learning about electronics.

Oooh boy… You’ve gone done it now… Now I like you.
Yea, I was not as clear or correct as possible. And yes, there were reasonable solutions, but I’m not here for solutions unless they fix faults in the design i have.

[sokoloff]

Aha, my bad. Should have had been clearer with what I meant with AMP. My apologies. Why “receiver” though? English is not my native language and “receiver” instead of “amplifier” does not sit well with me. I mean the main function is to amplify signal to drive larger speakers. Does it come down to just how it’s powered?

In English, an amplifier is exactly what you describe: a device that takes a small signal and makes a large signal out of it.

In audio, a receiver is an amplifier with a bunch of functionality sitting in front of it: switching inputs (CD, DVD, DVR, etc), often an AM/FM/HDRadio receiver [where the name probably came from], perhaps signal processing, maybe switching HDMI signals, maybe a volume control, and then onto the amplifier stage.

It's not exactly wrong to call that an amp and in fact searching for "amplifier" on Amazon eventually finds a Yamaha receiver on the first page of results [barely]. Receiver evokes that set of functionality exactly, where amplifier lead me down a mental picture of the simpler device. (And your English proficiency was so good that it never occurred to me that you weren't a native speaker; I didn't look for the little flag, so in that sense it worked against you a little bit, but your English is infinite better than my Latvian... )

Best with your project. 

[Zero999]

its difficult to follow your circuit, whats the K in circle (1mH) and capacitor (1ohm) next to it?

As the OP said, it's a relay. The circle is the relay coil and the capacitor-like symbol is the contacts.

That would be the relay with 1mh coil that has 1ohm resistance. Ignore those values. Again, i don't know why this application draws it like that.

Please don't use that symbol for a relay, unless you make the capacitor symbols look different enough. It's confusing.

I suggest using the following symbol for a relay:

http://www.reuk.co.uk/wordpress/electric-circuit/relays-and-renewable-energy/

[Otomaru]

Please don't use that symbol for a relay, unless you make the capacitor symbols look different enough. It's confusing.

I suggest using the following symbol for a relay:

I'm not happy with it either, but i have not found any option to change it in this application. My only options are switching between "ANSI Y32.2" and "IEC 60617", and neither of these standards have the drawing like we all know.

On another note... I modified the design (In attachment). Fun part is, i'm looking to change U3A with transistors, and maybe after that U2A aswell - that'll be fun ^^

[ebastler]

@Rerouter - Did you even look at the circuit? What are you doing?

I think he was trying to help you.
But you seem to have taken care of that.

Why is Mechatrommer the only one who seams to pay atention...

Let me venture a guess... 

Seriously, mate: You post a slightly convoluted circuit here, drawn in some strange application which uses a relay symbol nobody can possibly recognize as such; you give incomplete information about the intended function; and you expect people to spend their time to dig into this and help you.

You might as well try being polite, and thanking people for the time they have spent on your behalf -- even if their response is not what you had expected to get.

[Otomaru]

Let me venture a guess... 

Seriously, mate: You post a slightly convoluted circuit here, drawn in some strange application which uses a relay symbol nobody can possibly recognize as such; you give incomplete information about the intended function; and you expect people to spend their time to dig into this and help you.

You might as well try being polite, and thanking people for the time they have spent on your behalf -- even if their response is not what you had expected to get.

Here's what i have in 1st post:

• Here's my circuit.
• Here are it's goals.
• Here is my input, power descriptions and what the relay is for (meaning the circuit with LED is there only for simulation feedback).
• Please validate my circuit - what can be done better, what safety measures i miss? I don't want to burn either of my devices.
• Also it would be great if you could recommend a better OP-AMP and voltage regulator. Maybe you know the perfect transistor as well.

True, what sanwal209 posted could be put under "what can be done better", but later i clarify why that's not the path for me. Also him saying "You can do this with only a single relay" makes me think he did not read past my bullet points.
Here comes the man, Mechatrommer. He says it's difficult to follow - ok, valid point, but he asks about the unclear things (mysterious relay (k), probes), he did not assume anything. He found dangers in my circuit and told me how to avoid them and i thank him for that again.
Rerouter seams to be off topic. Not talking about my circuit, but how, in idea, to achieve the functionality i listed as my circuit goals. Goals i had already achieved.
sokoloff has my respect. He leveled with me. I also thank him for making me discover my receiver has "restore power after power loss" and pointing out a "missing feature" of my design (not turning off receiver when it's already on).
Hero999 just talking about the relay. I thought more people could decode the K in circle after i say there's a relay and the zender diode in parallel with the unknown thing. The application is Multisim, i have no idea why it does not have drawings that every one knows.
ebastler is here as judge and jury. Most valuable contribution.

"slightly convoluted" - Yes, slightly difficult to follow. So what? Am i allowed to ask only about simple things?
"uses a relay symbol nobody can possibly recognize" - I understand that could get in the way, but that does not make the whole circuit a mystery. It got clarified pretty early on.
"you give incomplete information about the intended function" - Uhmm... What's incomplete about the bullet points i have in 1st post? You meant that i called it AMP, not receiver?
"and you expect people to spend their time to dig into this and help you." - Isn't this sub forum (Beginners) meant for this?

I know it's a forum and it's up to the free will of people to help, but when i say "Evaluate my control board, pretty please?" and "Please validate my circuit - what can be done better, what safety measures i miss? I don't want to burn either of my devices." i did not expect people just going "It's difficult to follow" or "It's complex, do this instead".

[Zero999]

and you will damage Q2, if PC_USB is 5V from PC USB, put limiting resistor to the base.

Roger. Can any one explain why that's damaging? Also should i do something to protect signals from USB and AMP_ON?

It's damaging because the base of Q2 doesn't have anything to limit the current. The base-emitter junction of a BJT is just a diode junction which needs to be driven by a current limited supply. Just connecting it directly to the 5V USB supply will kill it.

[Otomaru]

and you will damage Q2, if PC_USB is 5V from PC USB, put limiting resistor to the base.

Roger. Can any one explain why that's damaging? Also should i do something to protect signals from USB and AMP_ON?

It's damaging because the base of Q2 doesn't have anything to limit the current. The base-emitter junction of a BJT is just a diode junction which needs to be driven by a current limited supply. Just connecting it directly to the 5V USB supply will kill it.

So it comes down back to ohms law (and semi conductor tolerances)? Man... i should be more aware/mindful of it.

[Mechatrommer]

thanks Hero for helping me answer the question. this thread went confusing just as the circuit. ok now i understand the relay, apart from the many probe point names there, i still cant see how the user try to switch it off

Don't turn it back on if i turn it off.

so i still dont know where to start, no user switch can be seen. sorry for my incompetency.

[Otomaru]

i still cant see how the user try to switch it off

Don't turn it back on if i turn it off.

so i still dont know where to start, no user switch can be seen. sorry for my incompetency.

In case you missed the updated circuit - It's here.

So the turn on pulse comes from R1 C1 and R3 Q1 and is created only when 5V power appears from USB (If you want i can attach some graphs with signals when i get home), the pulse gets silenced with Q4 if there receiver is on (2v where i have AMP_SIGNAL_ON probe).
Turn off signal comes from where i have the AMP_SIGNAL_ON (2v when receiver on, 0 when off) probe and is silenced by Q2 while there is power in USB.
These 2 signals combine in to SWITCH_SIGNAL (while signal high, relay switch will be engaged - is what went through my head, thus the name).

Trying to explain further has given me multiple better new ideas that i'll try out in weekend (Usually work leaves me too drained), but here's the rest of explanation for the current circuit.

Now in order to turn it off when my PC turns off and there is no more power i need another power source for relay - so the AMP_PSU comes in (PSU as in power supply unit cause it comes from a smaller board that powers standby phase and turns on the bigger transformer when the receiver is on).
Now in order to interpret the off signal only shortly after the PC is off and not while i want to use the receiver for other inputs while PC is OFF - i have R2 C2 and U2A that provides power for U3A output.
Now all that's left is U3A that Interprets SWITCH_SIGNAL only while PC is on and shortly after i turn it off, signaling the relay driver (D1 R4 Q3).

[Ian.M]

Some stuff is best done with a MCU.    When every feature you need is making your circuit more complicated, and changes needed because your spec isn't finalised are resulting in you having to rip up and redesign large chunks of your circuit, you could have saved a lot of time and effort by putting the logic and sequencing into a MCU.  Its the ideal application for one - nothing needs to happen particularly fast. 

You would power the MCU from the standby supply and sense all the voltages (e.g. main PSU output, USB Vbus etc.)  via potential dividers or in the case of the USB Vbus, via an optocoupler so the USB connection doesn't create a ground loop and risk introducing hum.

You need to have a good understanding of the tuner/amplifier's button matrix and IR remote sensor if present.   Tapping into buttons with relays is kludgy and complex, so if it can be avoided e.g. by an optocoupler in place of the relay, or by generating IR RC command signals and mounting an IR LED where it reflects back off the IR window in the front panel into the existing receiver, its preferable.

Generating the IR RC signal could offer you other benefits, e.g. allow you to send commands for automatic input selection.   If the unit has LEDs you could easily tap into that indicate which input is selected, (or if you can find a schematic and trace the input switching circuit to find the control signal for the analog switch that does the actual input selection), you can add additional features e.g don't switch off automatically if an input other than the PC is selected.

[Otomaru]

When every feature you need is making your circuit more complicated, and changes needed because your spec isn't finalised are resulting in you having to rip up and redesign large chunks of your circuit

That's called learning, something i really want with this project. And i'm having fun doing so thus far. Worth™

Tapping into buttons with relays is kludgy and complex

I don't know what you pictured but that sounds nothing like what i have going on.

IR is future plan, but in between this and that i want to create another project using arduino and then creating android and windows applicatons.

Optocoupler - That's a new one for me. Using that i can be much surer about safety of my devices, thanks for the tip, Ian.M.

[Zero999]

Have you ever used an MCU before? If the answer is no or not much, then you'd still be learning a heck of a lot, possibly more relevant to modern electronics, than by doing it the old way.

Have you tried simulating the circuit? If so what does the simulator give you? Does it work as expected? Is the current or power dissipation in any of the components excessive?

[Otomaru]

Have you ever used an MCU before? If the answer is no or not much, then you'd still be learning a heck of a lot, possibly more relevant to modern electronics, than by doing it the old way.

Never used. To be honest i'm not sure what the acronym is for, i found multiple meanings (regarding tech). I'm sure I'll get to learning about MCU eventually, this time I've set my mind to do it the hard (sort of) way.

Have you tried simulating the circuit? If so what does the simulator give you? Does it work as expected? Is the current or power dissipation in any of the components excessive?

I have LED there (LED1 V5 R9) for simulation feedback. It indicates when and for how long the button press is simulated - works like a charm. As to currents... I'm not too sure what to make out of them, every where i measured thus far i get under 1mA. Some places even down to to e-9 - Maybe i should revisit kirchoff's law and calculate manually. Think there were 3 ways to calculate power, i remember only the kirchoff's name, i some what knew them something like 6 years ago.

Could be i don't know enough about semiconductors to make sense of the currents. Will focus on currents when i have more time/energy.

...It was Kirchhoff's current law (KCL), Kirchhoff's voltage law (KVL) and then there was a method where you simplify the circuit down to one power supply and one combined resistance.

[sokoloff]

MCU is microcontroller. (Most relatable example is the heart of an Arduino, an Atmel microcontroller, but there are many others.)

In the spirit of the "restore power after power loss", I realized last night that no one had talked about using the trigger output on the receiver (not all are equipped) as a signal into your circuit that the thing is already on.

Most trigger outs carry +12V DC when the zone is on and are open circuit when the zone is off. This would be a good source for whatever system needs feedback on whether the receiver is powered or not. Have a look on the back of the receiver and see if you have this output. (And while you're there, look for RS-232 or ethernet control as well... )

[Otomaru]

Most trigger outs carry +12V DC when the zone is on and are open circuit when the zone is off. This would be a good source for whatever system needs feedback on whether the receiver is powered or not. Have a look on the back of the receiver and see if you have this output. (And while you're there, look for RS-232 or ethernet control as well... )

Have not found anything like that, nothing distinctive anyway. I'll play around with optocouplers, they have given me a new breath of enthusiasm, still lacking in energy though.