[Done] Salami's 1st GBZ Modded-HDMI UART Shift-Buttons Brightness Control

[salami738]

One question - How do you intend to reduce/increase volume if using headphones?

I will send special commands (example: Shift+Button Up) from the arduino via I2C to the raspberry.
Then i use a script on the raspberry to change volume with the linux mixer.


My solution has the following advantages:
- Stereo sound on the headphones
- Correct mixing of Stereo to Mono for the loudspeaker
- You can add a MOSFET between headphone jack switch and amplifier power in, so you dont have to power the amplifier, if you use headphones
- You don't need a pot, you can add resistors instead, so the headphone output can have the same loudness as the speaker

BUT also has its disadvantages:
- Changing of headphone volume needs the linux mixer
- You need an arduino leonardo or switches for vol+ and vol- connected to the raspberry
- More software needed


A perfect solution would be to use a linear amplifier, then you can connect L- and R- together (no BTL one, like the PAM8403).

[codeman0624]

I uploaded an image for you: .

The important part is not to use the ampifier for the headphones, and you dont need that, because the display can drive headphones.
The amplifier is only needed for the loudspeaker. And because the loudspeaker needs mono, i mixed the stereo signal with the 10k resistors.

Did you actually use this exact schematic? I'd be curious if it worked. It looks like the datasheet for the PAM8403 recommends DC blocking capacitors on the inputs. And sometimes headphone jack outputs (like out of the HDMI screen) are biased around a DC voltage, rather than around ground. I don't know any of this for a certainty, just something to keep in mind if it doesn't end up performing well or giving you good sound. You could potentially replace the 10k resistors with something like 10uF capacitors and see what it does.

[vnman]

I was thinking of turning the AMP from speaker amp to headphones amp and use the headphones jack with switch to turn off the speaker when headphones plugged in. This way you can have stereo speakers, the 1W tablet speakers.

OR do the headphones pass through, connect the speakers direct to the AMP output to have stereo and utilize the MUTE on the amp to turn off the speakers (or use SHDN to shutdown the amp) when you want to use headphones. I would have thought that you do not have the need to adjust volume on the headphones once you have the volume level the way you want, I do not adjust volume on my headphones when I listen to music on my mobile phone.

[salami738]

I was thinking of turning the AMP from speaker amp to headphones amp and use the headphones jack with switch to turn off the speaker when headphones plugged in. This way you can have stereo speakers, the 1W tablet speakers.

OR do the headphones pass through, connect the speakers direct to the AMP output to have stereo and utilize the MUTE on the amp to turn off the speakers (or use SHDN to shutdown the amp) when you want to use headphones. I would have thought that you do not have the need to adjust volume on the headphones once you have the volume level the way you want, I do not adjust volume on my headphones when I listen to music on my mobile phone.

Maybe you can use this list of articles about using PAM8403 as a headphone amp:
- http://chromo.cc/crate/crate-sound-headphone-amplifier
- https://electronics.stackexchange.com/q ... dphone-amp

But none of them gave me an exact solution for headphone-switching-jack plus speaker. So i tested my own (diagram in the photo), and it works fine.

[salami738]

Today i fixed most of the high energy usage issue of the display.
Content is in: viewtopic.php?f=44&t=4242#p51445

I am very happy with that. Gives me a 25% bonus on battery runtime. Had 3hours (with 4800mAh battery from Galays S2) before.

[chaosratt]

So what are your new consumption levels?

[salami738]

So what are your new consumption levels?

Measuring equipment / components used:
- Raspberry PI Zero W
- PAM8403
- Arduino Leonardo Clone
- Uni-T UT139C multimeter
- HDMI screen from KUMAN/Amazon at 80% brightness

Before the HDMI display mod:
In game: 3,7 to 3,9W (depending on battery voltage - banggood power boost is not very efficient at low battery voltages)

After the HDMI display mod (1.8V regulator replaced):
Emulationstation: 720mA at 4,2V battery voltage = 3,024W
CPU full load: 860mA at 4,2V battery voltage = 3,612W
In game: depends on the games cpu load (between the two values).
-> average: 20% savings

After the HDMI display mod (1.8V and 3.3V regulator replaced):
Emulationstation: 670mA at 4,2V battery voltage = 2,814W
CPU full load: 800mA at 4,2V battery voltage = 3,360W
In game: depends on the games cpu load (between the two values).
-> average: 25% savings

[fdeluxe]

Wich HDMI screen do you use? I have a kedei screen but I havent noticed an way to adjust brightness.

[salami738]

Wich HDMI screen do you use? I have a kedei screen but I havent noticed an way to adjust brightness.

Hi, we are currently reverse engineering a similar display in: viewtopic.php?f=44&t=4242. Another user already asked about the backlight on the Kedei without backlight button. Atm we need more time to figure out, how the backlight driver works. Can you start a new thread with pictures of your display, where we can see the chip numbers?

[LilJosh]

@salami738
Any tips on how to get the screen to fit correctly into the case? I just started my build and have been having issues with screen clearance even after cutting pcb. Also Very nice build so far!