Sony Arouje

a programmer's log

Archive for June 2016

Home made DC – DC converter for Microprocessor

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One important tool when you deal with Microprocessors are, regulated power supply. To power my standalone Atmega’s and test the working I assembled a regulator in a breadboard along with Atmega. I cant relay on some thing running in a breadboard, a loose wire can create tiring troubleshooting. So I decided to build a permanent solution by creating a PCB and assembling the components.

My requirement is simple, connect a 12v adapter and I need 5v and 3.3v output. The 3.3v should provide a minimum 300mA. I have to use this power supply to power ESP8266 or any module that uses 3.3v. I am using LM2575 to provide 5v and LM1117 for 3.3v. Theoretically LM2575 can withstand upto 40v.

Below is the Schematic.



Here is the PCB I created and assembled at home.

Printed side


Lacking some soldering skills, still learning how to solder well.



I can give input voltage via the DC Jack or screw terminal. Three female pins at the right hand side provide 5v, GND and 3.3v. Forgot to include a LED to show the voltage status.

Written by Sony Arouje

June 30, 2016 at 11:42 pm

Digital I/O Expander for Arduino

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When we work with processor like Amega328 or ATTiny85 we will come to a situation like we are running short of GPIO pins. One option is to go for 40pin processors like Atmega16/32/324, etc. But there are some cons with 16/32, these chips doesn’t have PCINT (Pin change interrupt) and we cant use software serial. If we are not dealing with Software serial then we can use these MC’s without any issues. Some of the experiments I am doing, deals with Software serial, so I decided to use Atmega328. But I need more Digital I/O pins. To get more IO we can pair Atmega328 with GPIO expanders like MCP23017 or MCP23S17.

Keep in mind that MCP23017 talks via I2C and MCP23S17 talks via SPI. I prefer I2C as it uses two pins of my Arduino, SCL and SDA. SPI needs 4 pins, MISO, MOSI, SCK and RESET. Also in my system there are several other chips connected to I2C bus and thus deals with only one type of communication.

Lets see how to connect MCP23017 to Arduino

MCP23017 Pinout


As you can see we have 16 GPIO’s in MCP23017, 1-8 and 21 to 28.


  • 5v to pin 9
  • GND to 10.
  • Arduino SCL to pin 12
  • Arduino SDA to pin 13.
  • MCS23017 RESET pin to pin9 with a 1k Resistor.

Now we need to set the I2C address of this pin. You can connect upto 8 MCP23017 by changing connection to A0 to A2 (pin 15 to 17). For e.g. connect all three pins to GND will get an address of 0, connect A0 to VCC and A1 and A2 to GND will give an address of 1 and so on.

Here I am connecting all the pins to GND and I get an address of 0.





Here I am not detailed the connection to Atmega328. I focused on the connectivity between 328 and MCP23017. To see how to run an Atmega in standalone mode, check this post.

Edit: As Anon suggested in comments sections, I added a pullup resistor to SDA and SCL lines. I2C is open drain and without a pullup resistor the system will not work.

Arduino Sketch

I used Adafruit library to interact with MCP23017, you also can directly interact with expander by just using wire library. There is a good post explaining how to write data to MCP23017 without any library.

#include <Wire.h> #include "Adafruit_MCP23017.h" Adafruit_MCP23017 mcp; void setup() { mcp.begin(0); mcp.pinMode(1, OUTPUT); } void loop() { delay(1000); mcp.digitalWrite(0, HIGH); delay(1000); mcp.digitalWrite(0, LOW); }


Here port 0 is referring to pin 21.


Here I talks about I2C connectivity but you can also use SPI using MCP23S17.

These expanders are not limited to Atmegas we can use it with Raspberry pi’s or any other processors that supports I2C or SPI communication.

Happy hacking…

Written by Sony Arouje

June 14, 2016 at 10:41 am

Posted in Arduino

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Schematic of standalone Arduino with FTDI Programming

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I recently wrote a post explaining how to setup an Arduino in a breadboard. This post will show the schematic of the system. It’s a very simple system with minimal components. Here I used Atmega 32a. To program the chip I used an FTDI module.




To program the chip via FTDI module, we have to bootload it first. I used an Arduino Uno as the ISP, I have a home made board to bootload or program Atmega 40 pin family processors.

Once the chip is programmed it can be directly powered by a 9 or 12v DC Adapter. Here I used LM2575 switching regulator to step down the source voltage to 5v. Switching regulators are very energy efficient and produce very less heat compare to linear regulators like LM7805. I am powering the system using a 12v DC source. If there is no adapter then the module can be powered from the FTDI module by shorting the jumper.

Here I configured the processor to run at 16MHZ external clock. If we are using 8MHZ internal clock then we can avoid the crystal and the two 22pF caps.


Happy hacking…

Written by Sony Arouje

June 3, 2016 at 9:48 am

Posted in Arduino

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