Serial Port in Ubuntu - Using Terminal

February 20th, 2018

We are often required to use Serial COM port in embedded system ( Like console booting in i.MX6). A USB to serial board comes handy in such case. First find out which Serial port corresponds to the hardware using

ls -la /dev/ttyUSB*

It is most likely going to be /dev/ttyUSB0

Next install putty

sudo apt-get install putty

Once it is install, you can launch putty using the following command

sudo putty /dev/ttyUSB0 -serial -sercfg 115200,8,n,1,N

This example assumes you want baud rate of 115200, 8 bit, no Parity

If you want to use the App instead, you will need to do following '
1. install gksudo
sudo apt-get install gksudo

gksudo is the gui compatriot of sudo

Next we need to modify the file /usr/share/applications/putty.desktop

Open /usr/share/applications/putty.desktop

sudo gedit /usr/share/applications/putty.desktop

Change the line

Exec=putty

to

Exec=gksudo -k -u root putty

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Order Notixed

February 5th, 2018

Notixed is up for sale at Reference Designer

Order The Notixed: ( Shipping in US is $4 for first and $1 for each additional)

Notixed - Turn Rpi to USB device
Notixed - Turn Rpi to USB device
Turn Pi Zero into USB device using Notixed, Shipping is $4 in US
$3.50

Out of US : The shipping is $6 for first and $3 for each additional unit.

Notixed - Turn Rpi to USB device
Notixed - Turn Rpi to USB device
Turn Pi Zero into USB device using Notixed, Shipping is $4 in US
$3.50

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ArduinoPixed - Integrated USB Hub and Arduino for Pi Zero

January 30th, 2018

ArduinoOixed has 3 USB Ports and an integrated Arduino Nano circuit and thereby allows you to seriously enhance the usefulness of Raspberry Pi Zero.

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It comes with an On board LED, a Push Button Input and a Thermistor that can be used for temperature measurement.

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The Arduino functionality is implemented on ATMEGA328 chip and its Pins come on two Headers of 10 pin each.

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The block diagram below best captures its functionality

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Arduinopixed builds upon our earlier successful projects including Hubpixed and HubSerialixed. It addressed two of the major concerns of Raspberry Pi Zero users - Lack of useful USB ports and lack of A/D Converters.

The key design element is the pogo pin that connects ArduinoPixed to the Raspberry Pi Zero using 4 provided Pogo Pins. There is no wire, cabling or soldering required. ArduinoPixed can be used as an Educational tool, where you can use a Keyboard and Mouse to hook to Pi Zero and ArduinoPixed to start learning programming. You will not only be able to learn C using Pi Zero, you can actually write programs to check real world sensors, like smoke detectors.

ArduinoPixed is priced competitively at $21 for early birds at Kickstarter ( Normal price is $23 each). If you buy in bulk it is $42 for a pack of two ( and $95 for a pack of 5).

Some FAQ

Q1 - One of the kickstarter enthusiast asked - If I connect it with Raspberry Pi zero W, would the Arduino be able to send data to cloud over WiFi (of R Pi)?

Answer - The way it can potentially work is - Arduino will be throwing the data to Raspberry Pi on its Serial Port. As soon as Pi Zero W receives it, it can upload it to cloud.

If I get time I will try some demo of it.

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Order Hubserialixed

January 8th, 2018

Huberialixed is up for sale at Reference Designer

Order The Hubserialixed Blue: ( Shipping in US is $4 for first and $1 for each additional)

HubSerialixed - USB Hub + UART for Pi Zero
HubSerialixed - USB Hub + UART for Pi Zero
Hub + UART for Raspberry Pi Zero, Shipping is $4 in US
$10.00

Out of US : The shipping is $6 for first and $3 for each additional unit.

HubSerialixed - USB Hub + UART for Pi Zero
HubSerialixed - USB Hub + UART for Pi Zero
Hub + UART for Raspberry Pi Zero, Shipping is $6 out US
$10.00

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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.

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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.

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