Preface

OLED requires 14V and VMU Zero generates it using Boost Converter. Conversion efficiency and output voltage ripple are evaluated.

Test Setup

Procedure

1. Slide the Switch S1 to OFF position to disconnect the battery
2. Attach the USB cable
3. Display single color or white image on the OLED
4. Measure I_in / V_in at R17 and I_out / V_out at 14V output
5. [Test Case #1] Repeat 4 with varying the display image
6. [Test Case #2] Slide S1 to ON and remover USB then Repeat 3-5 

Results

OLED Power vs White Input Level

Efficiency #1 - VBUS vs 14V Output

Efficiency #2 - VBAT vs 14V Output 

Preface

TI BQ24075 Li-Ion Battery Charger is used in the VMU Zero V1. This device also integrates the power path management to supply regulated power to the system even the battery is depleted or detached.

Test Setup

Procedure

1. Slide the switch S1 to ON position to connect the battery
2. Attach USB cable and fully charge the battery
3. Probe VBAT and GPIO14 (TX) to monitor the system power status
4. [Test Case #1] Leave the screen at emulator selector

   Remove charger and plot the discharging profile

5. Charge the battery
6. [Test Case #2] Load Super Mario on NES Emulator and leave at demo
   Remove the charger and plot the discharging profile
7. Slide the switch S1 to OFF position to disconnect the battery
8. Probe VBAT and CHG# to monitor the charging status
9. [Test Case #3]  Leave the screen at emulator selector
   Slide the S1 to ON position and plot the charging profile

Results

Discharging Profile Case #1  - Idle at Emulator Selector

Discharging Profile Case #2  - Super Mario Bros on NES Emulator

It only lasts 20 minutes with the 150mAh battery. 500mAh battery will be considered for V2 design...

Charging Profile Case #3 - Idle at Emulator Selector 

Charing time will look very similar regardless of the tasks on the Pi unless total input current exceeds the limit of 1.3A which is configured at I_LIM pin.

Preface

VMU Zero is using the original piezo speaker in the VMU. Piezo actuator is essentially a capacitor and it requires higher voltage to drive.

Test Setup

Procedure

1. Set volume as 100%

   amixer cset numid=1 -- 100%

2. [Idle] Probe the GPIO18 directly at Pi output in idle state
3. [Frequency Response] Probe V_in at R21 and V_out at LT3469 output
4. Play pre-generated single tone wave file

   aplay sin_1khz_100.wav

5. Measure the sound level at 2cm proximity using SoundMetrer X on iPhone
6. Repeat step 3-5 with varying the frequency from 10Hz to 20kHz
7. [THD] Probe V_in at R21 and V_out at LT34469 output
8. Play pre-generated 1kHz wave file
9. Record the sound at 20cm proximity using WaveSpectra on PC
10. Repeat step 7-9 with varying the peak level of the wave from 10% to 100%

Results

Idle

Continuous 8.4kHz oscillation was observed at PWM output when no audio. Amplitude was about 1.6V and DC offset was around 1.60V.

Frequency Response - Individual

Peak volume at 5kHz.

Frequency Response - Sweep

Narrow peak frequency response from 3kHz to 6kHz. Anything below 2kHz is significantly attenuated with -20dB.

THD

THD was almost 100% when the volume is 50% level because the PWM output was clipped above 50%. This resulted 3rd harmonic tone surpassing the fundamental of 1kHz at the speaker output.