Archive for September, 2009

DIY BBQ Smoke Generator – 2nd and 3rd Attempts

Friday, September 25th, 2009

I’ve had a few more gos at making smoke and, well, there’s still work to be done.

2nd Attempt

not bad for 3 bucks

There were two main issues with the first attempt. The smoke was intermittent, and I needed to manually shake the ramp. In the second attempt I tried to take care of both problems with one stroke.  I mounted a fan to the underside of the ramp. This would induce air circulation, and the spinning would vibrate the ramp. I settled on the fan out of a a hair-drier. The idea was appealing for several reasons:

  • An old hair drier is $3 at the thrift store.
  • A hair drier uses 120V AC.  I wouldn’t need a separate source to power it
  • It’s a fan.

Fan mounted to ramp

So I got the fan out and mounted it to the ramp.  It turns out that this idea wasn’t all that good.

  1. Mounting the fan in the middle of the ramp like that did little to improve circulation.
  2. The fan didn’t vibrate all that much
  3. It turns out the motor was actually DC.  They use the heater coil as a resistor to get the voltage they need, then rectify it with a diode.  It’s a brilliant, low cost solution for them.  It was a pain in the butt for me.
  4. The fan was LOUD.  You know, like a hair drier.

So other than learning how a hair drier is wiried, attempt 2 was pretty much a bust. I got the same smoke performance from a louder unit that needed a 12V power supply.

3rd Attempt

The fan didn’t really do much in the second attempt. It didn’t vibrate, and didn’t improve airflow. In the 3rd attempt I tried to fix both problems.

To increase the fan’s vibration, I decided to give it a little off-center weight. Inserting a screw into one of the blades shifted the center of gravity, and made it vibrate like a champ.  This didn’t do anything to help the noise / circulation issues though.  I try to be nice to my neighbors whenever I can, and 4-5 hours of vibrating hair drier noise just isn’t nice.

So I shifted gears. Instead of a constantly vibrating fan with on-off heat, I decided on an intermittent vibrating fan with more consistent heat. Since the initial smoke issues were caused by the On-Off heat control, maybe a more constant heat would lead to constant airflow / smoke. The Fan was relegated to vibration duty, turning on periodically to help the wood settle.


I built an arduino sheild (yes I used an offset header) to:

  • Send a 25% output to an SSR controlling the heaters. 
  • Vibrate the fan for 5sec every 10 min (more than enough to help the wood settle)

Great plan right?  I got everything set up, saw the smoke start, and walked away for 30 min.  Anyone know what happened next?  Anyone?  Yes.  You in the back.  The heaters added more and more heat to the chamber?  More than the air could remove,  even though the airflow was increasing with temperature?  You’re right!  I had suspected that this might happen, just not so quickly. 

…I came back to a fire.  It was contained within the box, and the box was alone on an a stone patio.  There wasn’t any danger, but the fan was cooked.  damn. Here’s some carnage photos where you can see the vibration screw:



So What Now?

I was hoping to be able to macgyver my way through this thing using aluminum foil and tape.  I’m going to have to up my game a bit.  In future attempts I’m going to start from overkill and work my way down, rather than the bottom up method I’ve been using.   So that means:

  • Really sealing the chamber.
  • Using an external fan
  • Using dampers to control airflow in and out.
  • Mounting the vibration mechanism OUTSIDE the fire box so it doesn’t get smoke/fire damage
  • More precise temperature control.  That’s right.  PID control.  I said overkill.  I meant it.

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DIY Barbecure Smoke Generator – First Attempt

Thursday, September 10th, 2009


Some serious progress has been made. We have smoke! It’s nowhere near done, but the results are encouraging. Here’s what’s been done since the last post.

Toaster Tear-down


The toaster I used cost me $10 at the thrift store. The first order of business was to take everything apart. 20 minutes with a screwdriver and some wire cutters, and I was left with the components I needed:

Stripped down

  • A heat-resistant box
  • 2 heating elements
  • A thermostat
  • An extra piece of sheet metal for the ramp (formerly the toaster’s outer shell)


All that stuff is in every toaster, and it’s all I really needed. This was a high-end model apparently, so there was a bunch of extra electronic components in there too. Lots of goodies for future projects. I won’t bother listing them all, but take a look at this picture. Not a bad haul for $10!

Heating Element Relocation

Relocated Heaters

With everything apart, I could start construction. Per the design, the heating elements were relocated to the bottom corner of the chamber. I needed new holes, and as you can see from the picture, I did a terrible job. I should’ve used a sheet-metal drill. Instead I used tin-snips. Oh well. The holes are in the right place, and the heating elements fit.

Ramp Construction

Fabbed RampRamp Inserted

The sheet metal that used to form the oven’s outer shell was cut and bent to form the wood-feed ramp. The inner walls of the box are contoured, so it took several tries to get something that fit nicely.

Thermostat Relocation

Relocated Thermostat

The last thing to do was move the thermostat. Since all the heat was going to be localized in a new place, I figured the thermostat should be nearer to it. I made a new hole in the center of the back, and mounted it there.

Time to Test!


Other than worrying about electrocution and burns, the testing phase was pretty straight forward:

  • I put 3 pieces of apple wood on the ramp so they were touching the heater.
  • Most of the holes in the hot boxwere then sealed with aluminum foil. I left holes for air intake and exhaust.
  • After plugging it in, it took maybe 10 minutes to find the right thermostat setting. I slowly upped the temperature until there was a constant flow of smoke.
  • Beyond that it was just sitting around and basking in the smokey aroma.



Of course there’s lots of work still to be done, but I’m really happy with this first attempt.

The Positive:

  • Those 3 pieces of applewood gave me 5 hours of smoke. I only had to intervene twice; shaking the box a little to get the wood to the heaters. Other than that it was continuous, automatic smoke!

Room for improvement:

  • The smoke density wasn’t constant at all.  When the heaters were on there was a lot more smoke formation (Heat + increased convective airflow.) When they we off the smoke tapered off.
  • Needing to manually shake the ramp violates one of the main design criteria I’m shooting for. This thing should “operate unattended.”
  • Currently the thermostat is out in the open, making it susceptible to ambient temperature changes.
  • It’s a little dangerous.  There’s exposed 120VAC all over the place.

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DIY Barbecue Smoke Generator – Project Kickoff

Tuesday, September 8th, 2009

Smoke Gen

Unlike most of the projects I’ve done in the past, this one is going to be a multi-poster. There’s just too many ins, too many outs. What’s the project? Turn a toaster oven into a high-quality barbecue smoke generator. Aaaaaand go!

First of All, Why Bother?

I’ll concede there’s a certain Zen-like satisfaction that comes from using only fire.  Constantly tending and tweaking,  making sure everything’s right.  I’ve done that, and with some success.  what I want now though, is consistency.  I want to start the process knowing there aren’t going to be any headaches.  I want automation.  It’s a travesty I know, but I’ve come to terms with that.

Design Criteria

Here’s what I’m going for. If I can get the smoker generator to do the following, I’ll consider the project a complete success. It should:

  • Operate Unattended for 8-16 hours.
  • Generate consistent smoke.
  • Allow for adjustable smoke density
  • Accept standard wood.  (No custom bricks, no sawdust, etc…)

Easy right?

The Plan

Smoke Gen Principle

The design I’m going to try is pretty similar to what you’d see in a commercial smoker. The wood is on a ramp that leads to a heating element. A restricted amount of air is allowed to flow past the wood. Because there’s incomplete combustion, lots of smoke is generated. As wood is consumed, ash falls away and new wood takes its place. Gravity may be all I need for that to occur, but I’m guessing I’ll need to vibrate the ramp.

Stay Tuned…

It’ll be interesting to see how it goes. Subsequent posts will detail the construction process, as well as testing and any re-design. If it all fails in a huge ball of fire? Well that will be covered as well.

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Anatomy of a Digital Thermometer Probe

Sunday, September 6th, 2009

After years of faithful service, the probe on my kitchen thermometer was starting to fail. I have a spare, so the failing one went in a drawer. The other day I was thinking about making my own temperature probe for another project, and figured now would be a perfect time to cut open that old probe to see what’s inside!


Probe Internals

I took the probe down to the ‘ol hackerspace and gave it quick cut on the bandsaw. With the outer sheath open everything just slid out, and I got a look at the internals:

  • Thermistor
  • plastic sheath
  • shielded/insulated single conductor wire

Shielded Single conductor

That last one threw me for a loop.  A SINGLE conductor wire?  I thought for sure there would be two insulated conductors inside that shielding.   It turns out they actually use the shielding as one of the conductors.  In the picture below you can see where the negative lead (I presume) is attached to the shield.

Thermistor Closeup

So there you have it.   Current travels out through the insulated wire, and returns through the shield.  The resistance of the loop is determined by the temperature the thermistor is seeing. The base unit infers the temperature and displays it.

You Mentioned “Another Project?”

Oh right, this is a project blog. The idea for a probe project is this: I make barbecue. During the ~16 hour cooking process I’d like to have 4-5 probes in the meat at various depths. In this way I could show the temperature gradient throughout the cooking process. If I make my own, the probes would be cheap enough to make this project feasible.

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