Dreamcast VMU Pi [Completed]

Show off your completed VMµ, or post your build logs here!
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obsidianspider
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Re: Dreamcast VMU Pi

Post by obsidianspider » Tue Sep 05, 2017 8:52 am

I just spent all of Sunday soldering magnet wire. A microscope would have helped.
Screen Shot 2017-09-05 at 10.50.46 AM.png
VMU soldering
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satri360
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Re: Dreamcast VMU Pi

Post by satri360 » Tue Sep 05, 2017 2:30 pm

obsidianspider wrote:
Tue Sep 05, 2017 8:52 am
I just spent all of Sunday soldering magnet wire. A microscope would have helped.
Beautiful job!

satri360
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Re: Dreamcast VMU Pi Build Guide - Power

Post by satri360 » Sat Sep 09, 2017 11:37 am

satri360 wrote:
Sun May 28, 2017 4:55 pm
TDK VLC5045 is installed on the original PowerBoost and the height is tall as 4.5mm. I'd recommend to replace it with a smaller 6.8uH 2020 (5050 in metric) power inductor so that we have more space in the tiny VMU. I used H=2.2mm 6.8uH Murata LQH5BPN6R8NT0 https://www.digikey.com/product-detail/ ... ND/5797750. WURTH 744042006 could also fit but I haven't tested. Performance results will be posted later.
Power inductors
I searched shorter power inductors in DigiKey library and picked 2 candidates - One is 2.0mm Murata LQH5BPN and another 2.0mm WURTH.
Here is the quick table of critical parameters for them.
vmu_power_inductor_table1.png
vmu_power_inductor_table1.png (65.34 KiB) Viewed 4418 times
Both Murata and WURTH has lower rated current probably due to the size restrictions. I calculated the peak current using the formula described in the TPS6109x data sheet under the similar design requirement but limited the minimum input voltage from 1.8V to 2.5V. Adafruit LiPo will be dead at 3.0V and I added 500mV margin for safety.
I_L = I_Out x V_Out / (V_Bat x 0.8) = 0.5*5.15/(2.5*0.8) ~= 1.3 [A] where I_Out = 500mA and V_Out = 5.15V.

Rated current of Murata LQH5BPN is higher than this peak current with more than 20% margin. However WURTH 744042006 will saturate at 1.2A and may not function as expected in the extreme conditions when the input voltage is very low as 2.5V. This won't be an issue if we ensure the minimum input voltage at 3.0V though.

Setup
Connected the regulated power supply to the VBAT input of the PowerBoost and wired the USB Fan as an alternative load since I could not find the Electrical load around. This USB Fan has a neat knob to control the fan speed. I have measured the I_Out = 148mA when fan speed is the lowest and I_Out = 345mA when fastest.
vmu_power_test_setup.png
vmu_power_test_setup.png (21.13 KiB) Viewed 4418 times
Results
Output ripple of the Murata inductor is 20% larger than the original TDK VLC5045 particularly at higher input current. This is probably due to the lower saturation/rated current of the Murata inductor and it loses the inductance quickly at higher current.
I also observed original DC-DC was in the discontinuous conduction mode (switch is off) in low input current while Murata is always in the continuous mode. I am not quite sure if this is caused by the higher DCR but this is a good example of the tradeoff of size and the performance. Output voltage is still stable at 5.1V and I conclude that Murata inductor works well based on the measurements.
vmu_power_inductor_results.png
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Last edited by satri360 on Fri Sep 15, 2017 7:59 am, edited 1 time in total.

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moosepr
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Re: Dreamcast VMU Pi

Post by moosepr » Sat Sep 09, 2017 3:46 pm

Wow, that's some in depth testing! You could switch the power boost for a generic charge/protect board. They tend to be smaller, the pi is happy with an input as low as 3v, and you gain a little run time too. The pi only cuts the 5v down for the CPU anyway. Apparently the 5v is only really needed for proper USB standard compliance
Get a small cheep LCD in your project https://www.sudomod.com/forum/viewtopic.php?f=22&t=2312
Wrap it all round a battery https://www.sudomod.com/forum/viewtopic.php?f=13&t=2292
Or use a custom PCB to make it really small https://www.sudomod.com/forum/viewtopic.php?f=13&t=2512
or make it really really really really tiny!! https://www.sudomod.com/forum/viewtopic.php?f=13&t=2919

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kite
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Re:

Post by kite » Mon Nov 13, 2017 8:10 am

Hey how is this project going? This was another project that inspired me to do my own :) let me know what you think viewtopic.php?f=13&t=4613

satri360
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Re: Dreamcast VMU Pi

Post by satri360 » Sun Nov 19, 2017 9:16 pm

kite wrote:
Mon Nov 13, 2017 8:10 am
Hey how is this project going? This was another project that inspired me to do my own :) let me know what you think viewtopic.php?f=13&t=4613
Kudos to you!

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Re: Dreamcast VMU Pi Build Guide - OLED

Post by satri360 » Tue Nov 21, 2017 12:48 pm

satri360 wrote:
Sun May 28, 2017 4:55 pm
Rework
I've realized that ground path is too poor to give stable 13.5V supply for the OLED driver. Add short wire from pin#2 of U3 to the closest ground such as GND pad of R7.
vmu_oled_pcb_rework.png
Added rework instruction for extra ground connections for the DCDC.

satri360
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Re: Dreamcast VMU Pi [Completed]

Post by satri360 » Sun Nov 26, 2017 6:52 pm

satri360 wrote:
Wed Mar 22, 2017 1:35 am
I am working on the Sega Dreamcast Visual Memory Unit (VMU) as it might be a good fit for Pi Zero.
I've finished the build guide. Please check each sections for the full instructions.
Any feedback or comments would be welcome!
vmu_assy_final_test1.png
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Barryasymn
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Dreamcast VMU Pi Completed

Post by Barryasymn » Fri Jul 12, 2019 2:22 am

I have a JGR lanyard from last year. I have some console history miniatures of the Dreamcast as well.

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