#mq3

[brentunderjaw]

DANNY PUDI MYTHIC QUEST 3.03

[mkkorantanen]

Mikko Queue - 3 / ?

[brentunderjaw]

DANNY PUDI MYTHIC QUEST 3.01

[brentunderjaw]

DANNY PUDI MYTHIC QUEST 3.02

[stefanebe]

View this post on Instagram

The backyard and the front door are open, the temperature is perfect to have dinner and chill outside. I'll be on the set until 11am #risbovibe . . . . 🎼 : MQ3 Feat @redmangilla : Everyday (Reggie & Roc Remix) #classictune . . #risbovibe #music #community #food #frenchinnewyork #Redman #MQ3 (à Risbobk)

[ctellesworld]

NS_Wauseon-OH_Depot_M3Q_UP1982_031115-3

M3Q with the Mopac Heritage unit passes the depot at Wauseon. In the picture, some local railfans gather for a picture of it. 1 of 3 Wauseon, OH - Depot

[tymkrs]

Drink Me Breathalyzer Take 2!

The funny thing about the Drink Me is that it's a miracle that it actually works.  After the folks in the tymkrsIRC took the schematic apart they had some choice words:

"This is one of the least readable schematics I've seen to be honest" ^o^

http://tymkrs.tumblr.com/post/62067063344/drink-me-breathalyzer-take-1

So there were clearly some issues with that schematic.  And we decided to change things around.  

First I added an extra LED to take advantage of the fact that the LED bar driver can drive 10 LEDs.  

And then instead of having a potentiometer that could calibrate the signal, I put a load resistor.  Now according to the datasheet, it needs to be 200k.  So that's what I drew up.  I still kept the calibrating potentiometers for the loref and hiref

I got it soldered up and everything.  And then all of the lights stayed lit no matter what I did to calibrate things.  According to insurgent's research he found another person who said "The MQ-3 datasheet says to use a 200K ohm resistor, but anyone who’s used this sensor knows that this constrains the measured voltage to a tight, high range. I recommend a 10K ohm resistor."

"The datasheet for this sensor shows that the resistance across the sensor is between 2K-20K ohms, so an RL value of 10K ohms will provide a wide voltage output range."

There's also a few ways you can see if something's wrong with the load resistance - to see if there's too much.  First take out the led driver chip.  Then look at the voltage coming from the sensor and compare it to Vcc when you have no alcohol and when you do.  Put one probe to GND, and one probe to pin 5 (signal line on the LED driver).  I got 4.55 volts for both what was coming from the sensor and for VCC.  Per @insurgent: "With 200k load you are only going to have a range of like 4.5 to 4.9 with 5v supply"

SO! We changed it to a 10k.  Now that wasn't the easiest thing because apparently I'm a bit of a barbarian when it comes to desoldering SMT components and I totally lifted the pad off when I desoldered the 200k resistor.  Whisker suggested I scrape off some of the purple soldermask from the wire that the messed up pad was supposed to connect to, and then connect with some solder.  So we got the 10k connected that way, thanks @wireengineer!

And then we measured things again - still with the LED driver chip out.  One probe to GND, and one probe to pin 5 of the socket (which is where the sensor's signal would meet the LED driver chip).  Once without alcohol, and once with.

Without alcohol we measured: 2.32v....140mA being drawn by the circuit

With alcohol and all lights on: 4.35v....>200mA being drawn by the circuit

So after tweaking the lo ref and hi ref potentiometers, we got it so that it reacted appropriately to alcohol being in the air! Wahoo!

Resources: 

http://channel9.msdn.com/coding4fun/articles/A-Tweeting-NET-Micro-Framework-breathalyzer

http://nootropicdesign.com/projectlab/2010/09/17/arduino-breathalyzer/

http://sensorworkshop.blogspot.ca/2008/04/sensor-report-mq3-gas-sensor.html

http://www.danielandrade.net/2010/03/07/building-an-breathalyzer-with-mq-3-and-arduino/

[tymkrs]

Drink Me Breathalyzer Take 1!

So after finishing the HeartMe, I thought it'd be hilarious if I could do some sort of OrganMe series.  And naturally thought about the liver, because well, alcohol is processed through that and what better way to test for alcohol than with a breathalyzer.  Now I've never seen one or needed to blow in one because I'm not really a drinker, but I thought it'd be funny to make one.

And then I looked at the liver.  And it is an uuuggggly organ.  Like, awkwardly shaped and I'm not sure I'd buy my own liver-shaped board, so I thought, next best thing, wine bottle!

I decided to use the MQ3 sensor which is this widely accessible, hard-to-calibrate sensor with a datasheet with too little information.  The main things that I can tell from the datasheet is that it works off of 5 volts and that before it works I need to power it for at least 24 hours.  Connection wise, we've got this schematic to work off of:

So I can choose either A or B to hook up to a DC5V source and then the opposite to hook up to something that can read the signal as well as a potentiometer RL which should be according to the datasheet, around 200k.  

One thing I wanted to do was of course incorporate LEDs, and I've had a little bit of experience with the LM3914 and so I thought I'd used it to drive a bunch of LEDs.  No problem right?

Here's my schematic.  With the help of JohnS_AZ we added a couple of calibrating potentiometers.  RV2 calibrates RLo and RV3 calibrates RHi.  It's like changing the range of what voltages the LED bar driver shows.  I however added RV1 because I thought I'd calibrate the signal.  

When I put it together, it actually still worked! (https://www.youtube.com/watch?v=mhxA_tR6Lj8 2 minutes in)

Now, there are a few things that are super wrong with this schematic.

Good practice is to label the pins of the ic with the pin's function so you know what pin is doing what.

This led driver drives 10 LEDs.  I only have 9. And pin 1 of the LM3914 is supposed to drive a LED, but I have it going to V+...woops.  Essentially, if you have too much alcohol, it shorts out the power!

RV1 is pretty much unnecessary because on both the schematic and the board, the signal from the sensor is essentially going into LM3914 pin.  Potentiometer RV1 is essentially just biasing the signal.  I should instead just have a 100-200k resistor (like what the datasheet says I should have).  Though I will probably go for fixed instead of pot.

It is however pretty!

But I would like it to work and you know, not short out :p. So I'm going to make those changes and then we'll try again!!

@atdiy/@tymkrs