Though we closed functional testing back in September, we shifted focus to more production-ready related items in October. Here are most of the things that we have worked on to get the DVT ready!

Power Delivery In and Out

In the EVT we had planned to allow power-in from two USB-Cs, the one on the top and the one on the bottom and have them both support PD In/Out at even higher voltages. This was one big challenge that didn’t yield for the longest time, we understood some IC-level and design limitations but instead of force fitting the requirements, we decided to simplify the power delivery part so that we can give sufficient power to the Comet and its peripherals and a reasonable power out.

Here are all the changes in the DVT -

• USB Type-C (Bottom)
  • Power Input, PD-compatible with support for in and out including higher voltages upto 20V
    • Dedicated USB 3.0 bandwidth, so you have a full 5 gbps un-shared
    • Supports OTG and Dual-Role
    • Always ON
• USB Type-C (Both 1, and 2)
  • Non-PD, Type-C data port
    • Shared USB3.0 bandwidth
    • Host-most only, with power out upto 5V@2A

Having a more capable bottom type-C port makes is super helpful for an external dock, which I am personally looking forward to!

Power Consumption

Once we solved delivery, our next stop was consumption. Optimal battery usage is something I wont ignore now and later. Almost all of November we have been busy testing, troubleshooting and here are the results -

• The Comet’s current consumption in active state is about 0.8W with the core peripherals up - SOC, RAM, EMMC without the display turned on.
• Now when you turn the display on and at max brightness, the power goes to 2.2W.
• Quiescent current when it is turned off or suspended to RAM drops to 20 mA (0.08W), which means you can probably get ~8 days of standby.

We have also tested active, suspend and sleep modes for below components -

• Audio Codec ✅
• Display ✅
• LTE Modem ✅
• USB Hub ⚠️ - We hit a snag with this patch. We have replaced the controller in DVT.
• WiFi 🚨 - The WiFi module goes to sleep when not in-use but the underlying SOC’s
• SDHC does not go to sleep. We are working with NXP on this.
• Wake on WLAN ✅ - We can wakeup the device from sleep via WiFI, we successfully tested this by trying to ping the device over the network.

LTE Integration

We have been testing the LTE modem (Quectel EM05) since past 2 months, and we have been able to get all the below working -

• Making calls and sending SMS
• High quality audio via USB at 16 KHz
• Waking up the device when a SMS or Call arrives
• Provisions for LTE and GNSS antennas are added and tested

Here are some demos -

Water and dust protection

In the DVT’s design we have added some levels of water and dust protection with the following changes -

• All the USB-Type-Cs are now waterproof
• We have removed the speaker vents from under the screen and added the speaker vent that will be covered with a water resistant and hydrophobic mesh
• There are no vents or air openings across the Comet
• The headphone jack and mini HDMI will be protected with a non-removable silicone cover
• The display will be sealed using silicone to ensure no water can get in.

We think this can get us upto splashproof levels!

Thermal Dissipation

We have finished our thermal dissipation design for the DVT, this introduces a big change in our internal housing design. The primary heat sources are the SOC, RAM, eMMC and the secondary being the M.2 module which could be a NVMe, LTE or an AI Accelerator. To get to efficient thermal dissipation we have done following changes -

• The middle tray is now entirely Aluminium from the inside, coupled with an efficient heat pipe that can help spread the heat quickly. An added advantage being a lot more protection from impact!
• The plastic body will now be a composite of PC + PBT (50/50) where the PBT polymer will be a Thermally Cool Polymer that can help radiate out some of the heat to the outside.
• All of the contact areas will be insulated with foam on the inside, so you don’t touch a hot surface
• Here are some simulation results when the processor is operating at 3.5W (though it is never going to exceed 2W).

Components Testing

We finished our testing of all components customized for the Comet -

Display

• Earlier this month @Akshay from our GUI team pointed out that our display is just too red and too bright, and some of you might have noticed with the earlier screenshots. We worked with our manufacturer to fix this and you can see the results below
• In this process we also manage to get access to gamma control commands over DSI to the display!
• We have also got the display heat under control by applying a graphite sheet to the back of the display.

Battery

• We have completed our testing of charging and discharging cycles for our customized 4100 mAH battery, we even got ourselves an accurate DC load for this 😄
• The battery gives ~15 Wh, and we were able to discharge at upto 4A successfully

Voltage	Current	Time
3.94 V	4 A	02:05:00 PM
3.81 V	4 A	02:15:00 PM
3.64 V	4 A	02:25:00 PM
3.51 V	4 A	02:35:00 PM
3.41 V	4 A	02:45:00 PM
3.32 V	4 A	02:55:00 PM
3.23 V	4 A	03:00:00 PM
2.96 V	4 A	03:05:00 PM
Cut-off	2.8 V	03:07:00 PM

Discharge Time	Battery Temp (°C)	Energy
1 hour 1 min	40	15.05 Wh

Pogo Pins

To improve the already strong grip with the extension, the male pogo pins on the extensions will now work on a reduced operating force of 20g from 40g, making the total force ~800g (20gx40)

Camera ❌

We have not been able to test our cameras end-to-end, though we can get sensor data but due to some hardware design and ISP compatibility issues we couldn’t get the right images. This is on our list to review in the DVT.

Pre-certification

In mid-November, we also got the EVT tested for all regulatory and certifications requirements. Happy to share that we did quite well, to my surprise!

• Power Frequency Magnetic Testing ✅
• Electro Static Discharge ✅
• EMI Immunity ✅
• EMI Emissions ☑️ - some more protection is needed, you can see below in some cases we are cutting it too close with the limit.

This helps make sure that our design is ready for FCC, CE, UKCA, IC, … certifications that are crucial before we start shipping. In fact most results were so good that we plan to get it cleared for Commercial and Light Industrial class.

More Improvements

• A lot of you are keen to try using the Comet as a DIY phone, I am one of them too. I thought we all could use a 🧭 magnetometer apart from the 6-axis gyro+accelero.
• We couldn’t do modular emmc, but we now have DIP switch for boot mode that can support booting from SD Card as an alternate.
• We have reduced wires inside the housing and simplified repair by shifting to pogo pins based connections for the speaker and haptic motor.
• The 5V on the pogo-pins are now always-ON
• All Kill Switches are now tested and support run-time on and off.
• We have added support for hot SIM detection
• We solved the headphone detection issue in our audio codec driver, now the audio out can switch to headphone on insert.

I will be sharing a separate Mechanix OS update later. There is a lot brewing there too, but just not ready to serve (yet!)