Rotary volume control for the Raspberry Pi

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1. Will this work with these type of pot?

   10k B103 3-pin – https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcSha2H8vu2tjdDgKgJrk_r9yOF24JH76gm3h58DSKpJzSRvepY7wA

   Or

   10k B103 5 pin – https://ae01.alicdn.com/kf/HTB1.eMEHVXXXXayXXXXq6xXFXXX7/Dial-potentiometer-b103-10k-double-16-2mm-gear-dianthuses-potentiometer-5.jpg_640x640.jpg

   Thank you!

2. Honestly, I don’t know for sure – never tried. However, potentiometers only have a certain range that they can travel through – a min and max rotation before they stop. Rotary encoders, on the other hand, have infinite rotation so would allow you to scroll as much you want to either way. Also, rotary encoders produces digital signals whereas potentiometers would be analogue. So I suppose it depends on your need.

   This thread may be of some info to you: https://www.element14.com/community/thread/55374/l/potentiometer-instead-of-rotary-encoder?displayFullThread=true

3. Awesome, easy and very well explained! Thank you so much… I ran into one Prolem though:
   I get a negative Volume for minimum volume (-10239) when I do “amixer cget numid=1″. I cannot call ” amixer -c 0 cset numid=1 -175″ with a negative number, for it gets misinterpreted…. I have no soundcard, but use regular output via build in sound: “cat /proc/asound/cards”
   gives
   ” 0 [ALSA ]: bcm2835_alsa – bcm2835 ALSA
   bcm2835 ALSA”

   How can I use the negative value for volume-min. so I can make the volume lower than now? Right now I can only go from 400 to 0, leaving a considerable amount of volume left…..

4. Hi Andy,

   I was wondering if you could help to understand my problem is, as I followed your tuto and the rotary is working but not acting on sound at all.
   (Raspberry 3)

   Here is the output of with the above commands :

   pi@raspberrypi:~ $ cat /proc/asound/cards
   0 [Headphones ]: bcm2835_headphonbcm2835 Headphones – bcm2835 Headphones
   bcm2835 Headphones

   pi@raspberrypi:~ $ amixer -c 0 controls
   numid=2,iface=MIXER,name=’Headphone Playback Switch’
   numid=1,iface=MIXER,name=’Headphone Playback Volume’

   pi@raspberrypi:~ $ amixer cget numid=1
   numid=1,iface=MIXER,name=’Capture Volume’
   ; type=INTEGER,access=rw——,values=1,min=0,max=65536,step=1
   : values=65536

   And once I launch the script I can see the knob acting

   pi@raspberrypi:~ $ python volume.py
   105 (51%)
   Muted
   Unmuted
   100 (48%)
   105 (51%)
   110 (53%)
   115 (56%)
   110 (53%)
   105 (51%)
   100 (48%)
   95 (46%)
   90 (43%)
   85 (41%)
   80 (39%)

   I have not modify your script.

   Sound is coming in the raspberry through Bluetooth (A2DP) and out via the jack plug.
   Thank you for your help

   cheers

5. @srvduplex you say you haven’t modified the script at all, but I think you may need to. In the script there is a min/max value:

   # vals from output of amixer cget numid=1
   min = 0
   max = 207
   

   which I got from the values output by using amixer cget numid=1.

   When you ran that same command, your min/max was shown as min=0,max=65536. So in the script, make the lines look like:

   min = 0
   max = 65536
   

   and see how that works out. You may also need to adjust the line:

   preVolume = volume = 100  # give it some volume to start with
   

   So that the 100 is around 3200 or something, given that your max is reported as 65536.

6. Hello!

   Thank you for a very interesting site!

   I have the same question as klettervirus.

   I get a negative Volume for minimum volume (-10239) when I do “amixer cget numid=1″. I cannot call ” amixer -c 0 cset numid=1 -175″ with a negative number, for it gets misinterpreted…. I have no soundcard, but use regular output via build in sound: “cat /proc/asound/cards”
   gives
   ” 0 [ALSA ]: bcm2835_alsa – bcm2835 ALSA
   bcm2835 ALSA”

   How can I use the negative value for volume-min. so I can make the volume lower than now? Right now I can only go from 400 to 0, leaving a considerable amount of volume left…..

   Can you please help me?

   Best regards
   Johan

7. Hi Johan, thanks for posting a comment.

   To be honest, it’s been a really long time since I’ve played around with this as the project I was going to use it on didn’t go anywhere, so this answer is just a guess…

   I had a look at the amixer man page, and it’s possible to give a percentage value, such as:

   amixer -c 2 cset numid=1 40%
   

   So instead of incrementing a numeric count based on min/max values from a call to amixer, you could try just going up and down from 0 to 100%, something like (the very, very untested code as I’m just winging it right now):

   
   from RPi import GPIO
   from time import sleep
   import subprocess
   
   clk = 5
   dt = 6
   btn = 26
   
   min = 0
   max = 100
   
   GPIO.setmode(GPIO.BCM)
   GPIO.setup(clk, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
   GPIO.setup(dt, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
   GPIO.setup(btn, GPIO.IN, pull_up_down=GPIO.PUD_UP)
   
   isMuted = False
   preVolume = volume = 40
   clkLastState = GPIO.input(clk)
   btnLastState = GPIO.input(btn)
   
   def set_volume(level):
       subprocess.call(['amixer', '-q', '-c', '0', 'cset', 'numid=1', f'{level}%'])
   
   try:
       set_volume(volume)
       while True:
           btnPushed = GPIO.input(btn)
           if ((not btnLastState) and btnPushed):
               if isMuted:
                   volume = preVolume
                   isMuted = False
                   print "Unmuted"
               else:
                   preVolume = volume
                   volume = 0
                   isMuted = True
                   print "Muted"
               set_volume(volume)
               sleep(0.05)
           else:
               clkState = GPIO.input(clk)
               dtState = GPIO.input(dt)
               if clkState != clkLastState:
                   if isMuted:
                       isMuted = False
                       volume = 0
                   if dtState != clkState:
                       volume += 1
                       if volume > max:
                           volume = max
                   else:
                       volume -= 1
                       if volume < min:
                           volume = min
                   print(f"Volume at {volume}%")
                   set_volume(volume)
               clkLastState = clkState
           btnLastState = btnPushed
   finally:
       GPIO.cleanup()
   

   No idea if it'll work, and I cannot try it out as my pi and sound card are scattered around in a box or two somewhere - no idea where right now! 😀 But hopefully it'll point you in close enough to the right direction!

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