Experimenting with Gas Sensors and Arduino


We have 4 different Gas Sensors on our web shop: MQ-2, MQ-3, MQ-7 and MQ-135.

All they work on same principle: sensor element is heated and it’s conductivity change with the gas concentration.

The heater require 5V and have 31 ohm resistance, so your power supply should provide 200mA of current for the sensor.

Sensor have both analog and digital output, the analog output is 0-5V, the digital output is frequency related to the output value.

MQ-2 is sensor of LPG, Propane, Methane and Hydrogen gas and can be used for domestic gas leak alarms
MQ-3 is sensor of Alcohol and Benzine and can be used for breath analizer
MQ-7 is sensor of Carbon monoxide CO and can be used for car gases analizer
MQ-135 is sensor of NH3, NOx, Alcohol, Benzine, Smoke, CO2 and can be used for quality of air analizer

We did some experiments today with all four sensors connecting them to OLIMEXINO-32U4 (Arduino Leonardo compatible).

The sensors have 4 pins: AO – Analog Output, DO – Digital output, GND, VCC-5V

MQ-1 MQ-2

OLIMEXINO-32U4 should be switched to work on 5V.

Three wires are used: AO from sensor to A0 of Arduino, VCC from sensor to 5V, GND from sensor to GND of Arduino.

The sketch is simple:

int sensorPin = A0;
int sensorValue = 0;
void setup() {
 pinMode(sensorPin, INPUT);
void loop() {
 sensorValue = analogRead(sensorPin);

It reads the sensor value and print it on Serial terminal.

Note that when sensor are power up they need about 1 minute to settle, in this time the heater heats up the sensor.

We experimented with Isopropil alcohol, Benzine, Lighter Gas, human breath of two different persons :)

Here is the measured data:

MQ-2 normal air output  100
     Isopropile alcohol 540
     Ligher Gas         760
     Benzine            450
     Breath1            150
     Breath2            140
MQ-3 normal air output 180
     Isopropile alcohol 800
     Ligher Gas         400
     Benzine            700
     Breath1            220
     Breath2            270
MQ-7 normal air output  150
     Isopropile alcohol 750
     Ligher Gas         900
     Benzine            800
     Breath1            170
     Breath2            160
MQ-135 normal air output 130
      Isopropile alcohol 700
      Ligher Gas         760
      Benzine            450
      Breath1            150
      Breath2            140


the results are:

MQ-2 shows good sensibility to Lighter Gas

MQ-3 detects well Isopropile alcohol and Benzine

MQ-7 detects well Isopropile alcohol, Ligher gas and Benzine

MQ-135 detects well Isopropile alcohol, Lighter gas

New Product in stock: Open Source Hardware SMT-PROTOBOARD with many SMT component footprints and KiCAD files


SMT-PROTOBOARD is Open Source Hardware prototyping board with these features:

  • FR-4, 1.55 mm, gold plating
  • dimensions: 124.46 x 101.6 mm
  • SMT footprints:
  • LQFP 32, 44, 52, 64 at 0.8 mm step
  • TQFP 32, 44, 52, 64, 80, 100 at 0.50 mm step
  • x4 SOT23-6
  • x3  SOT89
  • x3 buttons 6×6 mm
  • micro SD card
  • mini USB connector
  • JTAG connector
  • UEXT connector
  • x6 LEDs 0805 + R0805
  • TSSOP 2*92 at 25 mils
  • TSSOP 2*32 at 50 mils
  • PROTO x3 16×4 0.1″ step
  • PROTO x2 16×8 0.1″ step

Board is designed with KiCAD and files are available at GitHub

New Products is stock: Desoldering pumps with teflon tips and copper core de-solder wick

Desoldering Pump 366-А

When you have to repair boards or replace components you need tools to remove the solder from the components.
We now stock two type of desoldering pumps: D-336A black plastic desolder pump from the picture above with plastic body and special anti grip foam coating and


metal body GS-136A

Both pumps are easy to use and make good vacuum force to remove the solder. Their pistons are with double air seals which guarantee no air leaks.


De-solder wick is another useful tool when removing solder, just put it on the component pin and apply heat with the soldering iron the copper core wick will suck all solder from the component.

It’s with 3mm braid fine wires and 1.5 mm length.

The Long anticipated RT5350F-OLinuXino is finally in stock and we have some more good news


RT5350F-OLinuXino development started loooooong time ago, we made the hardware very quickly and hit the wall with the software :)

The Hardware had two revisions, we knew that this IC is overheating and need external DCDC power regulator to release it from the heat, but we first decided to try how bad is it with the chip steps down the 5V to 1.2V with internal LDO, well…. the chip was easily rising to 60C at room temperature 20C, so we made revision.B where we add external DCDC and the temperature of the chip cool down to 40C, so far so good.

The next obstracle was WIFI tuning, Ralink have bunch of registers which are not described in the ‘datasheet’ but you have to know what do with them if you want to tune your WIFI to work correctly.

OpenWRT wisely skips this area of memory as each module vendor is responsible to write the optimal info for the chip in these. It took us about year to figure out what to write in these registers, including obtaining NDA info about the chip features.

The result is good, the chip makes link from up to 20 meters when in house and up to 50-60 meters in open air which is about the maximum of this small PCB printed antenna.

RT5350F-OLinuXino is now in stock and cost EUR 15 in single quantity.

We didn’t stop here, we made also EVB with two relays, button, RT5350F-OLinuXino socket, UEXT connector, USB host, two 100MB Ethernet ports and EXT connector with all unused ports.



The RT5350F-OLinuXin-EVB is also in stock and cost EUR 24 including RT5350F-OLinuXino in it.

Then we decided to make new version with just one Ethernet and LED display in DIN enclosure:


you can see it here how it looks in plastic box:


RT5350F-OLinuXino-DIN is still not complete but will be in stock soon (hopefully end of June). The price will be about EUR 35. It will be nice solution for home automation, serving array of ESP8266 sensors and BLE modules as OpenWRT supports 6LoWPAN.


A33-OLinuXino Open Source Hardware Linux SBC with Quad Core Cortex-A7 ARM processor running at 1.5Ghz


While we stopped the work on A31, we decided that A33 is promising device as it have Mali video and there is chance to have open source drivers and Linux support with hardware acceleration.

A33-OLinuXino is OSHW project and you can see the preliminary files at GitHub.

With size of 70×76 mm it’s small SOM like board, you can see the component arrangement above:

There are two 40 pin 0.1″ connectors: upped for LCD connector, lower for GPIOs, I2C, SPI, etc

A33-OLinuXino have PMU AXP223, A33 Quad core Cortex A7 running at 1.5Ghz, 4/8GB NAND Flash, 1GB RAM

On the left side you can see USB-OTG, LiPo battery connector, debug UART, button, micro SD card on the bottom

On the right side there are Audio IN and OUT connectors and flat cable connector with MIPI and CSI signals.

We still have no idea what it will cost when released as we don’t know how many layers will be the PCB, but we guess it will be in the LIME range i.e. about EUR 30

A31-SOM update


About year ago we posted on this blog about our work on A31 SOM module, a lot of time passed away so we would like to make clear statement about it’s status.

A31 SOM hardware was complete long time ago, but we found lot of bugs in A31 during the software development. Lot of things do not work as expected and the chip have overall poor performance. The video is with PowerVR which means there will be no Linux acceleration forever. All you will got running on it with hardware acceleration is Kernel 3.4 with Android. Memory do not work reliable above 200Mhz clock which is terrible performance. While we have hesitated if we have to put more effort on this chip we got notice from Allwinner that they discontinue A31 and A31s production which ended our hesitation.

A31 has very short life, Tom Cubie shared on IRC before while that Allwinner internally hate this chip with all it’s bugs too :) so I guess Allwinner also got relieve to get rid of it.

Leasons learned, we move forward :)

First Open Source Projects from Bulgarian government


The Bulgarian Government open source the code of some projects paid by the state for very first time.
The open source code is on https://github.com/governmentbg/
This happens with the support of общество.бг (society.bg).
Why open source is so important for the government projects? Because people will have access to the final code government spends tax money for and all technical knowledge people could have look what exactly is done. Many people could see the source and give feedback improving the security and functionality of the code.

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