Issues With Stereo Audio(Pi3+PAM8403+ Kedei HDMI)

[DeRock89]

The Power Boost can only supply 1A @ 5V right?

I could be wrong -

The Pi 3 uses ~750mA idle
PAM 8403 at max volume uses 12mA
pro Micro 5V 16MHZ uses 12mA or there about.
Kedei HDMI display - could not find info on power consumption. If you find out then you can work out how much ampere you need to power everything.

Yeah I tried to find info on what it pulls but wasn't able to either: So unless the screen pulls 200mA then everything should be fine right? What would be my options if everything actually exceeded 1A?

Do you think I will have further issues by using speakers rated at 4 ohm? It doesn't make sense to me if a 8 ohm speaker is rated 3 watts and a 4 ohm is rated 3 watts then they should both pull 3 watts, otherwise why rate it for 3 watts in the first place?

I've been thinking about this because I did some reading on speaker impedance and in normal audio applications, a 4 ohm speaker draws double the amps of an 8 ohm. If you tie two 8 ohm speakers in parallel then you get double the draw because it becomes 4 ohm. If 8 ohm speaker are tied in series then they become 16 ohms.

I'm also attempting stereo sound. I don't know if me using both + and - connections for both L and R with two speakers also increases the load. I don't understand what the bridged concept in the datasheet means.

[joeygbsn]

It all depends on if the amp can drive an 8ohm speaker at 3w. If you look at the datasheet it says that with 5v and a 4ohm speaker max power is 3.2w but with an 8 ohm speaker max power is only 1.8w. Looking at your diagram are you only using the fpc board to run power to the amp and screen? With the small traces and added connectors you may have a significant voltage drop across that once you get to the screen and amp.

[DeRock89]

It all depends on if the amp can drive an 8ohm speaker at 3w. If you look at the datasheet it says that with 5v and a 4ohm speaker max power is 3.2w but with an 8 ohm speaker max power is only 1.8w. Looking at your diagram are you only using the fpc board to run power to the amp and screen? With the small traces and added connectors you may have a significant voltage drop across that once you get to the screen and amp.

Can I just use resistors to to get that 3.2w down some? Either on the voltage supply lines to the amp or at the speakers so they won't draw so much currant?

[joeygbsn]

Yeah you could just put a small resistor in series with the potentiometer so there would always be some resistance. You'd have to test some values to find out what works. Or you could try powering the amp with 3.3v.

[vnman]

Just search for "PAM8403 Headphones amp" with Google, you need to turn the amp into headphones amp. This can be done with a few resistors and you can you switch headphones plug to mute the sound when headphones plugged in.

In the mean time you can put these lines in config.txt to reduce the screen powe consumption since it does not need to use GPU for down scale the video -

Code: Select all

# custom display resolution (480x320 looks good , and 720x480 is not too bad too,3rd res is: 810x540 )
#         /----------------- Width: 480px ( or 720px /or 810px)
#         |   /------------- Height: 320px ( or 480px /or 540px)
#         |   |   /--------- Refresh: 60Hz
#         |   |   | /------- Aspect ratio: 6=15:9 (1=4:3, 2=14:9, 3=16:9, 4=5:4, 5=16:10)
#         |   |   | | /----- Margins: 0=disabled (1=enabled)
#         |   |   | | | /--- Interlace: 0=progressive (1=interlaced)
#         |   |   | | | | /- Reduced blanking: 0=normal (1=reduced)
#         |   |   | | | | |
hdmi_cvt 480 320 60 6 0 0 0

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
hdmi_drive=2

Note the code is not mine.

[DeRock89]

Just search for "PAM8403 Headphones amp" with Google, you need to turn the amp into headphones amp. This can be done with a few resistors and you can you switch headphones plug to mute the sound when headphones plugged in.

In the mean time you can put these lines in config.txt to reduce the screen powe consumption since it does not need to use GPU for down scale the video -

Code: Select all

# custom display resolution (480x320 looks good , and 720x480 is not too bad too,3rd res is: 810x540 )
#         /----------------- Width: 480px ( or 720px /or 810px)
#         |   /------------- Height: 320px ( or 480px /or 540px)
#         |   |   /--------- Refresh: 60Hz
#         |   |   | /------- Aspect ratio: 6=15:9 (1=4:3, 2=14:9, 3=16:9, 4=5:4, 5=16:10)
#         |   |   | | /----- Margins: 0=disabled (1=enabled)
#         |   |   | | | /--- Interlace: 0=progressive (1=interlaced)
#         |   |   | | | | /- Reduced blanking: 0=normal (1=reduced)
#         |   |   | | | | |
hdmi_cvt 480 320 60 6 0 0 0

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
hdmi_drive=2

Note the code is not mine.

Is this code just for use temporarily because won't it reduce the brightness and graphics?

Do you want to Pm me your address so I can send you that FPV ribbon cable?

[vnman]

No it would not reduce brightness and graphics. Its job is to set the right graphics resolutions (what the screen support) on the pi so that there would be less work on the GPU on the screen trying to scale down. Note I am not talking about the GPU on the pi.

Suppose the Pi output is 720p via HDMI the screen would need somehow down scale this to fit 480 right? that is the job of the GPU on the screen and since it have to convert signal it has to use some power...

PS. Are you ok to ship the FPV to Norway? PM me with paypal so I can compensate you for the trouble.

[DeRock89]

Yeah you could just put a small resistor in series with the potentiometer so there would always be some resistance. You'd have to test some values to find out what works. Or you could try powering the amp with 3.3v.

On the input or output pins of the pot? What values do you think? I have some 1K and 10k resistors and a variety kit of all kinds of values ordered?

I wonder how low the sound will be when powered with 3.3v... I got a 10uF capacitor too to place on the power rail like in sotas build. I just wonder if I will have the same issues lololos build has of consuming a ton more battery by having caps installed. Lololos build is using two super caps though.

[VeteranGamer]

Just search for "PAM8403 Headphones amp" with Google, you need to turn the amp into headphones amp. This can be done with a few resistors and you can you switch headphones plug to mute the sound when headphones plugged in.

In the mean time you can put these lines in config.txt to reduce the screen powe consumption since it does not need to use GPU for down scale the video -

Code: Select all

# custom display resolution (480x320 looks good , and 720x480 is not too bad too,3rd res is: 810x540 )
#         /----------------- Width: 480px ( or 720px /or 810px)
#         |   /------------- Height: 320px ( or 480px /or 540px)
#         |   |   /--------- Refresh: 60Hz
#         |   |   | /------- Aspect ratio: 6=15:9 (1=4:3, 2=14:9, 3=16:9, 4=5:4, 5=16:10)
#         |   |   | | /----- Margins: 0=disabled (1=enabled)
#         |   |   | | | /--- Interlace: 0=progressive (1=interlaced)
#         |   |   | | | | /- Reduced blanking: 0=normal (1=reduced)
#         |   |   | | | | |
hdmi_cvt 480 320 60 6 0 0 0

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
hdmi_drive=2

Note the code is not mine.

Is this code just for use temporarily because won't it reduce the brightness and graphics?

Do you want to Pm me your address so I can send you that FPV ribbon cable?

just to add....

this is how i had my config for my HDMI build....
i personally didn't notice any issues with the brightness, and the graphics are what they are (still way better than a composite)




.

[vnman]

The config.txt settings is just to see if the power consumption reduced since there will be no down scale processing involves. That is up to @deRock89 to see which resolutions is acceptable.

As for the resistors you could follow this blog here - http://chromo.cc/crate/crate-sound-headphone-amplifier.

to simplify follow this pic -