Digital volume control and DACs

[chrispbass]

The story is not quite over, but more later.

 

[JohnRoberts]

Sounds like a win..... Good job.

JR

 

[chrispbass]

Sounds like a win..... Good job.

JR

Thanks John

 

[abbey road d enfer]

a good dose of stubbornness for good measure

Some call that ingenuity.

 

[chrispbass]

Some call that ingenuity.

Thank you Abbey

 

[JohnRoberts]

Persistence combined with the collective wisdom and experience of this remarkable forum.

JR

 

[chrispbass]

Persistence combined with the collective wisdom and experience of this remarkable forum.

JR

It’s exactly that John. I’ve a few more things to add, and bring this to its final conclusion.

Funnily though, this thread should now be probably moved back to the lab

 

[chrispbass]

Ok, so it’s working, and hopefully will continue to do so.



I did mention a “but” yesterday and here it is.



When operating the volume from the front panel there is a glitch when using the up and down (+ -) buttons. These are part of a small pcb with 6 tactile switches to operate cd, menus select etc. The glitch only occurs when using the down button to lower the volume.



The volume lowers, but after 2 or 3 presses it invokes a sub menu.



The obvious thing was to see if using the remote to change volume caused the same glitch.



Remote no longer working.



101 - test battery



Battery very low - CR2302 cell that I didn’t have a spare to hand at the time.



Ok, still a bit of gas in the tank, so take a look at the sub assembly.



Not much to it. 6 switches, a few resistors and a ceramic cap. A quick glance and it just seems (as far as I could tell) to be a resistor ladder(divider) with each switch connecting to ground, but haven’t traced it out.



Was, there a cracked solder joint on the switch pad?



I reflowed the solder joints and cleaned the pcb down with IPA, and left it to evaporate. I powered back on to find all hell had broke loose! Now there were many glitches from all the buttons. PWR down.



Obviously pcb still “wet” from IPA (doh!) but shows how sensitive the circuitry is…and in some ways a good sign, but back of mind still saying that perhaps there is an internal issue with the imbedded software/logic.



Put it down and sleep on it.



Today, pick up new battery.



Remote working.



No glitch when reducing volume.



Hooray!



Back to fault finding the front panel switches.



So that’s where I am now.



Got severely side tracked tonight so no lab time but will try and iron out what I hopefully believe to be a very small issue.



Need to get the pcb under the microscope for a proper visual.



Possible switch contact issue - bounce/resistance?



Sleep on it again

 

[scott2000]

but after 2 or 3 presses it invokes a sub menu.

Is it usual to use the volume buttons to get to the other menus?

Possible switch contact issue - bounce/resistance?

Old Apogee Rosetta switches will jump over several selections with one push. Very frustrating.
I'd guess the contact issue since you say the remote works fine but the accessing sub menus is kinda weird if it's not supposed to have that function?

 

[chrispbass]

Is it usual to use the volume buttons to get to the other menus?


Old Apogee Rosetta switches will jump over several selections with one push. Very frustrating.
I'd guess the contact issue since you say the remote works fine but the accessing sub menus is kinda weird if it's not supposed to have that function?

Thanks for the suggestions Scott. I’ll look deeper in to it. I’m just relieved that there is no issue when using the remote.

 

[MicMaven]

Is it usual to use the volume buttons to get to the other menus? ,,,
accessing sub menus is kinda weird if it's not supposed to have that function?

Wile Alex Guess No. 2039874 -- On some devices, amateur radio transceivers for example, buttons have multiple functions. For example, a short press may lower volume, while a longer, lingering press may bring up a MENU. In that case, lowering volume may require multiple short presses until you reach the desired level, whilst a long, lingering press may open a MENU, instead. Then again, I may be throwing a wild pitch and be way off bass. After all, I am just guessing! James

 

[JohnRoberts]

MCU push button switches often use weak internal pull-up current sources and switch closure to ground. Debouncing, etc is usually handled in software. A dirty/leaky PCB could confuse the binary hi/lo determination.

JR

 

[scott2000]

On some devices, amateur radio transceivers for example, buttons have multiple functions. For example, a short press may lower volume, while a longer, lingering press may bring up a MENU

For sure. But if the button isn't supposed to have that function, it would be weird if it acted that way..
I guess JR's description sounds like a possibility if not...

Maybe happened across a secret developer menu....

 

[JohnRoberts]

For sure. But if the button isn't supposed to have that function, it would be weird if it acted that way..
I guess JR's description sounds like a possibility if not...

I have no idea what exactly is going on and since the remote works, this seems more of an academic pursuit.

Over the years I have encountered sundry issues with momentary switches. Failure to register a switch hit if the impedance to ground is not low enough to force a logic low. I came up with software work around to resolve at least one such switch failure.

JR

 

[ccaudle]

MCU push button switches often use weak internal pull-up current sources and switch closure to ground.

This sounds like maybe it is using an ADC to only need one button to sense multiple different buttons:

it just seems (as far as I could tell) to be a resistor ladder(divider) with each switch connecting to ground, but haven’t traced it out.

A pullup to one pin which can be configured as ADC, and then the voltage at that pin depends on how many resistors are in series pulling the pin down. Or you could do it the other way, end of the resistor chain to Vdd, and a pull down at the ADC pin, the switches go to a "switch bus" instead of ground, and again the voltage depends on how many resistors are in series.
Would have to wait for Mr. PBass to trace out the circuit to confirm if that is the case.

 

[chrispbass]

I have no idea what exactly is going on and since the remote works, this seems more of an academic pursuit.

Good advice and taken onboard John

 

[chrispbass]

After spending a bit of time with the switch pcb (and taking onboard JR’s comments), I’ve decided that it’s not really worth pursuing.

In addition to the switches, I did reflow the molex connectors to the board and also did a system reboot (just in case), but it’s hardly a massive issue in the grand scheme of things and of course the remote is rock solid.

I feel that my luck may run out if I continue to pursue perfection, when in reality it’s almost a “non fault” or a teeny ghost in the machine, so I’ve decided to wrap this up and call it a day.

I’ve now got it all back together in the case and it was a nice moment to pop a CD in and fire it up properly as I’ve just been using headphones whilst on the bench.

I’ve learnt a lot from this project and although from the outset the deck was stacked against a +ve outcome, I whole heartedly thank everyone for your input/guidance/expertise and experience in helping “keep the ship steady” on this little voyage and for instilling the need to stick with troubleshooting 101 when I may have gone a little “tangential” at times.

thanks to the team…

@sahib
@Khron
@JohnRoberts
@Disco Volante
@thor.zmt
@Admiral-dk
@ccaudle
@scott2000
@abbey road d enfer
@MicMaven

Couldn’t have done it without you guys. The world has not been saved but another “mini victory” and reconfirming what a great community this is.

I haven’t told the owner it’s fixed yet, so tomorrow I’ll get it back to him and should be a nice surprise, especially as he’s been a bit unwell recently!!

Cheers all

Chris

 

[MicMaven]

. . . I’ve now got it all back together in the case and it was a nice moment to pop a CD in and fire it up properly as I’ve just been using headphones whilst on the bench. . . .

Oh , no old man . . . you cannot quit now! We have only just begun raking this one over the coals - we are not even close to reaching overkill . . . um . . . er . . .

OK, never mind. Glad it you got it working again! Cheers. Take Courage. James

 

[chrispbass]

Oh , no old man . . . you cannot quit now! We have only just begun raking this one over the coals - we are not even close to reaching overkill . . . um . . . er . . .

OK, never mind. Glad it you got it working again! Cheers. Take Courage. James

I did think I was wimping out James

Took it back to the owner today…he was a bit speechless to say the least!

Tbf, he rarely touches the controls on the front and rarely uses the CD, but either streams or plugs his laptop in through one of the aux ins.

Good to get it off the bench too, as loads of projects to take it’s place and a studio build starting v soon that’s going to pretty full on!

 

[sahib]

Well done.

I have not contributed anything but thank you.