Related
Recommended
Engagement
  • Author Author: tariq.ahmad
  • Date Created: Date Created
  • Last Updated Last Updated:
  • Views 2115 views
  • Likes 7 likes
  • Comments 17 comments

Tinkering vs Engineering: Can You Build a Laptop from Scratch? -- Episode-640

Clem's latest project takes a deep dive into laptop design, merging various components, such as a BLE keyboard, compute module, mouse, and a universal diagnostic screen into a custom-built laptop. However, the path to success wasn't without its challenges. 

Watch the Video:

Downloads | Bonus Video | Bill of Material | Discussion

The project required a unique power system. For that, Clem opted for multiple 2000mAh LiPo cells, instead of a single large one. To achieve the necessary voltages (3.3V@1A, 5V@2.5A, and 12V@0.5A), Clem faced the complexity of generating multiple voltages from a single-cell source. This involved designing a switching converter, a task he had never done before.. 

image

Troubles arose when attempting to parallelize the step-up converters. Clem's initial approach faced issues with voltage regulation and load-induced voltage drops. The struggle to balance multiple step-up converters led to unexpected challenges, impacting the overall system's stability. Despite successful testing of the charging circuit, integrating the system with an actual computer brought about further complications. 

image

Clem wanted to use a Sudosom module; however, development wasn’t quite complete. This prompted a switch to a Raspberry Pi Compute Module 4. However, the step-up converters failed to deliver sufficient current, causing the voltage to drop and the computer to brown out. Even switching to a CM4 Lite did not resolve the problem. 

image

In a last-ditch effort, Clem used resistors in an effort to control the voltage, but realized that the project demanded more expertise in power supply construction than he currently possessed. The undertaking highlighted the distinction between tinkering and engineering, emphasizing the need for precise measurements and in-depth knowledge in the latter. 

image

Clem's rapid one-month endeavor revealed the importance of a well-planned and fresh design for such complex undertakings. 

Downloads and Links:

Bonus Video:

Bill of Materials:

Product Name Manufacturer Quantity Buy Kit
MICROCHIP Power Load Distribution Switch IC, Active Low, 1 Output, 5.5 V in, 700 mA, 0.14 ohm, SOIC-8 MICROCHIP 5 Buy Now
MOLEX HDMI Connector, 19 Contacts, Receptacle, PCB Mount, Surface Mount Right Angle MOLEX 2 Buy Now
MIKROELEKTRONIKA Rechargeable Battery, 3.7 V, Lithium Polymer, 2 Ah, JST MIKROELEKTRONIKA 3 Buy Now
BOURNS Power Inductor (SMD), 10 µH, 2.1 A, Shielded, 2.5 A, SRR0745A BOURNS 6 Buy Now
TOREX DC-DC Switching Synchronous Step-Up Regulator, 0.65-6V in, 5V out, 0.5A out, 3MHz, SOT-25, 5Pin TOREX 6 Buy Now
TEXAS INSTRUMENTS DC-DC Switching Boost Step Up Regulator, Adjustable, 2.7V-14Vin, 600 kHz, 2Aout, SOT-23-5 TEXAS INSTRUMENTS 2 Buy Now
MICROCHIP Battery Charger for 1 Cell of Li-Ion, Li-Pol battery, 6V input, 4.2V / 500mA charge, SOT-23-5 MICROCHIP 3 Buy Now
TOUCHSCREEN 10.1 MULTICOMP PRO 1 Buy Now
MOLEX FFC / FPC Board Connector MOLEX 6 Buy Now
 

Actions
Parents

  • You've embarked on an impressive project and made an incredible project.

    However. Regarding your power supply, I took a peek at your KiCad files—just a few critical issues I see right away.

    I am using this converter for an example (so I can use designators.)

    image

    1. For the ceramic output capacitor (C28), you should have a relatively large CV 0805 (imperial) MLCC. A large CV means the highest rated voltage at whatever capacitance you picked. An 0805 has much less DC-Bias effect than a 0603 and is available with higher rated voltages. Since you have the space, I would also use a 0805 on the input (C29) as well.

    image

    2. That tiny ground trace on the capacitor is KILLING the supply. Everything should have a FAT connection to ground. The kind of connection that is tough to solder!

    3. You should not use traces for any of the switching signals! Everything should be a large copper pour. Even though you used larger traces, their inductance is a significant issue. For comparison, here is a partial shot of the board I made for the "How to make a noise-free SMPS" video:

    image

    In this case, I used a through-hole switcher IC (and this is a buck, not a boost--but the principles are the same.) Notice how the ONLY trace I used is for the feedback signal (which I don't think your fixed switchers have.)

    The massive Vout and GND pads at the top are the output filter capacitor. The Vout and SW at the bottom is the inductor. See how I drew massive copper pours for them?

    I would also encourage you to use large pours, NOT TRACES, throughout the distribution of your 5-volt rail.

    For example, here are the 3v3 and 5v rails in the Mega IIe's design:

    image

    (The empty space is GND, which I deleted for this picture.) Only in a few cases did I draw a trace from my fat pours to a chip.

    As a suggestion, I would have laid out the supplies something like this. (Don't copy this exactly. I just did it real quick.)

    image

    Since you have enough room, I would also suggest adding an extra capacitor footprint so you can add a second value.

    Last. I would encourage you to do two things if you're going to move forward with your own SMPS design.

    1) Make the SMPS as standalone boards first. You need to test them in isolation. You'll rarely get them right on the first try. Then you can replicate their design to the larger PCB.

    and the most important

    2)  Please, please, please, verify the operation of your switchers on an oscilloscope! Your DMM is lying to you!! Given how your PCB looks, I would NOT be surprised if your peak-to-peak noise was several volts, meaning you are hitting that poor CM4 with >10 volt transients! It's also possible your supply is oscillating from all of the inductance on the power distribution network (PDN).

  • in reply to baldengineer

    Oh yeah, the inner and bottom layers should all be ground. And there should be more ground stitching vias than you can count.

Comment Children