HunSerialixed Serial Port Add on Board details and Dimensions

December 3rd, 2017

Hubserialixed contains a USB to UART chip and a possibility to design and add your own add on board. Today we are going to give some more details and insight into it. Firs the Mechanical dimensions - this one will help you.

All dimensions are in inches.

And this is the section of the circuit for USB Hub to Serial Port.

The Circuit should also allow you to get the details of the 4 Pin connector Add one.


Raspberry Pi SD Card Power off Corruption and Solution

December 1st, 2017

All versions Raspberry Pi including the latest Raspberry Pi 3 and the Pi Zero W expect to be shut down gracefully, with a shutdown command something like

sudo shutdown now

This however does not always happen. We often pull the Power Chord or the cable may accidentally wiggle loosing the power connection momentarily. This results is SD Card Corruption. The more disastrous result is loosing your programs that you may have been working on for few weeks. This blog is about how to prevent this to happen using hardware method.

The Schematics shows the idea used to make this happen

The +5V Power is given to the Fuse F1. The Diode D1 is a Schotty Diode ( Part Number MBR230LSFT1G) that gives a 0.3V dropped as measured. The 4.7V Power is supplied to the Raspberry Pi Circuit through the 40 Pin Connector. The circuit will work at 4.7V as we have verified it, but if you have USB Devices this scheme may not work.

The Key element is the Super Cap C1, which is nominally a 5F Super Cap rated at 5.5V.

The Key equations that govern this circuit are as follows

1. The Fully charged voltage on the Capacitor is = 5V - Vd = 4.7V
2. The Processor works until the voltage drops until about 3.8V. The is delta V is 0.9V
2. The Current taken by Raspberry Pi 3 in steady state after boot was measured at 300mA
3. The Capacitor formula gives Q = CV

One we disconnect the power chord the Voltage at the resistor divider R1 and R2 drops from 2.5V to 0V. This goes to GPIO6 ( or any other GPIO that you may select). The processor can detect this and issues the shutdown command. Let us assume that the processor needs 10 seconds to completely finish the shutdown process. The total charge required is

Q = ix t = 300mA x 10s = 3 Coulomb

The Capacitor Value required is C = Q/V
or C = 3/.9
or C = 3.33 Farad

A Capacitor value of 5 Farad is adequate for this purpose.

Few Concerns

1. The 4.7 Volt is not an acceptable value and drop of 0.3V Across the Diode is not desirable. A FET based circuit is

The Circuit taken courtesy Electro-Tech .

With this circuit in place the Voltage drop will be only of the order of 0.07V. This is something we need to test.

2. The Capacitor may take high sudden inrush current, and therefore a small resistor in series with Diode may be worth considering.

3. The Capacitor should have low ESR. A typical capacitor tested to make the system work had ESR of 100 milli Ohm.

A typical implementation will consist of an Add on Board with 40 Pin Connector. A USB Micro connector can be installed in the Add on Board and and power may be supplied from the USB Micro connector on the Add ON Board in place of from that the Raspberry Pi Board.

Update 12/3/2017

It turns out that in place of the P-Channel MOSFET and the related circuits as a Diode, we could also possibly try Load Switch using Micrel MIC94040YFL-TR Part.

Notice the Internal Pull Down on the Enable Pin. When there is no power, the Enable Pin will be pulled down. There still be a resistor divider with the Enable Pin at the center point of the Voltage divider.


HubSerialixed - USB Hub + UART for Pi Zero W

November 15th, 2017

Nov 11, 2017

On January 24, 2016, we made first announcement of Hubpixed, a USB Hub - first of its kind product - for Raspberry Pi Zero. It had 4 USB Hubs and did not require and cable or connector. And although the USB Connectors were a little protruding, the area near the 40 Pin Connector was empty - and the 40 Pin Connectors could be accessed. When Pi Foundation updated their design to 1.3, the Pogo Pin locations were changed and we updated our design to support the updated Pogo Pin Position.

Subsequently, the Hubpixed evolved to HubPiWi in which we knocked off one USB Port and added support for Wifi. The HubPiWi Blue further enhanced it by providing support for Wifi as well as Bluetooth.

The launch of the Raspberry Pi Zero W, obsoleted the HubPiWi and HubPiWi Blue but hubpixed was still a useful product.

With this background we are today announcing today another product in the series, that we are calling HubSerialixed. Hubserialixed has 3 USB Hub Ports - which are same as the ones in Hubpixed - The forth USB port has been removed and we have a USB to UART Bridge chip. The RX, TX Pins of the Bridge chip come on a 4 Pin Header.

You can connect any of your add on device using the 4 Pin Header - it could be 433 MHz RF module or a thermal sensor or may be and ADC. Since this UART port works off the USB, you are not concerned about the inbuilt UART ports available on the 40 Pin Connector. In fact none of the Pins of the 40 Pin connector are required to be used.

We have kept the 40 Pin Connector area vacant - so that these pins are still available to be used if you wish to.

The UART Pins are provided as 4 Pin Jumper with following Pins

1. 3.3V


3. GND


There are two mounting holes in the design and you could possibly design a small add on board that will fit on the 4 Pin Header and the two mounting holes. This gives the design extreme flexibility.

In the initial prototype we had only 3 Pin. We had earlier assumed that the power supply was not required, which could have restricted the possibility of having an active add on board.

Here is how the initial prototype board looks like.

The project is expected to go live on kickstarter in a week time. Stay tuned for more information.

More Technical details

1. lsusb lists out the USB UART chip

2. Install minicom

sudo apt-get install minicom

3. See the device number for the USB Serial Port

ls -la /dev/ttyUSB*

4. Start minicom

sudo minicom -D ttyUSB0

5. You can now short the Tx ans Rx Pins and should be able to see the typed character echoed.


HP 15-bs020WM laptop on Walmart Black Friday Deals 2017

November 15th, 2017

The HP's 15-bs020WM will be one of the best laptop deals on the 2017 Black Friday if you could grab one. This is a 15.6-inch touch supported notebook and as usual for laptops of this kind, it comes with Windows 10 Home pre installed.

The processor is Intel Celeron N3710 and comes with 4GB of RAM. The Celeron models are less talked about ( compared to Core i3, i5 and i7) and will spend some time understanding about this processor. Before we do that bear in mind that the laptop comes with 4GB RAM, 500 GB Hard disk and had HDMI port.

The Celeron N3710 is a quad core processor with 1.6 GHz clock frequency and Burst Clock frequency of 2.6 GHz. It is a low power processor intended for thin laptops. The processor performs reasonably well though will not be as fast. For example compared to the core i3-7100U, a popular processor used in expensive think notebooks ( 2 Core, 4 threads 2.4GHz) it is about 1.5 times slower ( of course in processor intensive tasks). But the processor power should not affect other things like browsing and you should be able to feel it.

The other features are not high end but probably you could not ask for anything more in an under $249 laptop.

The stated battery life of 7 hours is decent - probably more than enough you will need in one sitting. This is made possibly with the low power processor. You could possibly get even better if you keep the display at lower brightness.

The 15-bs020WM comes with stereo speakers, and of course the Wifi. And although we do not need the Ethernet now in laptops, it comes with one for wired networking, just in case you need.
There are two USB 3.1 ports and a USB 2.0 port. Also available is a multi-format media card reader, and an audio mic and headphones port.

However, if you are looking to use this laptop for gaming for games that require more of a gaming horsepower, you will be disappointed. The integrated graphics at 400 MHz base clock is just not good enough.

Pros :
- Touch Screen Display.
- Long Battery Life
- Inexpensive

- Not very fast
- Not for gaming


PiSerialixed update and Hubpixed chatter

November 15th, 2017

For everyone on kickstarter who have backed PiSerialixed, we have an update - it has been shipped from our Manufacturing house and it typically takes like 3 days to arrive us. Our expectation is that it will arrive before the end of this week ( i.e. on or before 11/17/2017). I am keeping my finger crossed - I do not have the tracking number available yet and will be able to say with more confidence in a day time. In the mean time you can check the twitter account at - possibly by following it.

Sometimes ago we had posted about PiSerialixed needing a USB Type A to Type B adapter, that makes its usage more friendly. If you have not yet done so, you can pay $2 at our paypal at and indicate your backer number at kickstarter and we will include this cable with your shipment.

If everything goes well, the shipping should start no later than 11/20/2017. As earlier, USA residents will be the first recipients. We will be completing another successful project at kickstarter with Pi Serialixed.

The Raspberry Pi Series products first started rolling out with the introduction of Hubpixed on Jan 24, 2017 in my blog post. It was highly successful and its iterations were well taken of. It is still great product and continues to sell well. If you are using a Raspberry Pi Zero, this is something you would like to have in your lab.

I also had a chance to look at the mechanical case / enclosure for Hubpixed at thingsverse.

It is looking cute with a two part box. I do not have it in my hands. I will encourage you to follow the thingverse link where you can get the STL files. You can then use the STL Files to get it 3D printed. There any many avenues to get the 3D printed case ( I sometimes use ebay).

Feel free to write your comments.


Installing PiSerialixed on the Raspberry Pi Zero

October 29th, 2017

The Pi Serialixed has a 5 Pin Connector that is supposed to connect to following 5 Pins of the Raspberry Pi 3.

It is very important to make sure that we properly align the Pi Serialixed to connect to the Raspberry Pi 3. This is the correct way to connect.

The following two images show incorrect alignment and this is something we would like to be very careful when connecting.