An easy Soundlevel & Source Remote Control for iPad / iPhone

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Hi all

I would like to adjust level on my DIY preamp, not digitally, and control this from the iPad or iPhone - ideally from mPad or mPod, the mpd remote apps. There are way too much level differences from an album to another. Source selection would be a nice bonus.

I am using mpdpup on a Linux Laptop, and a WaveIO board to feed my SPDIF DAC then Pass Son Of Zen preamp,
The mpdpup is remotely controlled by mPad or mPod apps, works quite fine except the album data that is displayed is very limited (especially for classical). But that's another problem :usd:

What options could be imagined ?

I Am not sure if this part of the forum is the right one, sorry for that.

Kind regards
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Yes it is possible, however I am afraid not out of the box. It requires hacking electronics as well as software.

Alsa defines so called controls. The most common control is volume adjustment. MPD (the player you have chosen) lets you specify which one of the volume controls offered by alsa is operated by its volume control "slider" (mixer_type, mixer_device, mixer_control in mpd.conf). That is the simple part.

Now you need to build the volume control backend. I have searched net several times for a ready-made RS232-operated volume control. There are devices for home automation, I do not know about their quality and they certainly seem quite pricey to me, considering what they contain. It should not be complicated, perhaps even without embedded single-chip microprocessor (PIC, AVR).

And the software glue - can be in user space, operating serial port. There is a great alsa plugin for Arcam AVRs operating key controls via serial line. Arcam is perhaps the only manufacturer having published its serial line control protocol. Your code could be much more simple, you would need just volume control.

If someone knew of an already existing rs232 volume control kit, we could just write alsa plugin and have such device usable easily by linux audio players.
Thanks a lot phofman, I have to study deeper your comprehensive answer. I understand I could use the volume control on the mPad and that alsa would not act on the digital signal but divert the action required to another "port". Is that correct ?

However my Asus eeePC I use for mpd server does not have RS232, only VGA, USB and ethernet.
I searched quickly and found a USB => RS232 converter but worth 79$...
I will search again but I have a clearer idea how to make it.

Do you know a resource that explains in simple terms how Alsa works ? I have basically no experience with Linux.

I have a feeling this solution could be useful to many now that smartphones supersedes traditional IR remote control.


Hi guys

If I can't find help on DIYAUDIO on such an issue, where will I find it ?:confused::confused:

phofman has explained a possible way, none has experienced the concept he has drafted ? my coding skills are unfortunately too much below par, not to speak of Alsa Mixer :(

if its ok to plug my project (lol), you can start at and find the lcduino link along with the 'alpha 10 preamp'. this is a full relay based (r2r) attenuator, input selector, output selector and has some support for remote-remote control (over serial, that would tie in to a linux back-end webserver). this would be the 'phone' remote control side of things.

the source code is there and can be changed all you want.

I have some experimental code that links alsa mixer to the lcduino system. a daemon that runs on linux and watches 2 things: the mixer vol control slider on the system as well as the physical knob on the preamp. if one is updated, the other is made to update, and vice versa. the code for that is not released but I can make it available as needed.

I posted quite a bit about all this on amb's forum; you can see the posts under my username (same one) there in the delta1 and lcduino sub-forums.

the architecture I chose has a linux box as the middle system. it has a great IP stack, great webserver and good usb/serial support. you can use a raspberry pi as the middle linux box if you want.

I don't do bluetooth yet but it might be possible.

what I do like to use is xbee (zigbee) modules that are just serial-over-the-air, that is painless and reliable. you can connect an xbee to your pc's usb and another xbee to the preamp and they can 'talk' over the air even across a few rooms of a house.

ethernet is where the phone connection comes in (wifi or real ethernet). then into the webserver. then into a tcp-socket daemon job that is tied to the usb/serial/xbee port. then over the air to the preamp and back again.

nothing has rs232 anymore (lol) but usb/ttl serial is easy and cheap ($5 sometimes on ebay) and that gets you ttl level serial, which is exactly what the preamp wants.
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