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Simple and Cheap DIY system for under $20
- Thread starter MarkN
- Start date
RobM (YankeeRob)
TVWBB Super Fan
ANOTHER UPDATE!
This morning I went to take some measurements for the comparator circuit. I slapped an ohmmeter on the thermistor and was getting flaky results. It was still set up in its test harness. I had it plugged into a CD ROM motherboard audio cable and the connection was funky so I fixed it and decided to run the experiment again.
Testing part 2:
I decided to focus on the temp range of 230 to 250 because it seems that it where this will operate. Same test harness as before. Also, my setup uses a 10K multi turn pot but you might want something with finer granularity.
Anyway:
I brought the temp up to 253 and adjusted the pot so the fan just barely turned off. To do this you need to go back and forth a little bit.
With the fan now off i VERY SLOWLY began to bring the temp down in 5 degree increments. The fan turned on again at 240!
OK Great. Now slowly bring the temp up and see where it turns off. It turned off at 248.
Bring temp down again and it turns on at 237.
So it seems the circuit as shown WILL work with a variance of 10 to 15 degrees!!
I still want to strap the comparator on the front end to tighten it up a bit. Hopefully I can do that today.
-rob
This morning I went to take some measurements for the comparator circuit. I slapped an ohmmeter on the thermistor and was getting flaky results. It was still set up in its test harness. I had it plugged into a CD ROM motherboard audio cable and the connection was funky so I fixed it and decided to run the experiment again.
Testing part 2:
I decided to focus on the temp range of 230 to 250 because it seems that it where this will operate. Same test harness as before. Also, my setup uses a 10K multi turn pot but you might want something with finer granularity.
Anyway:
I brought the temp up to 253 and adjusted the pot so the fan just barely turned off. To do this you need to go back and forth a little bit.
With the fan now off i VERY SLOWLY began to bring the temp down in 5 degree increments. The fan turned on again at 240!
OK Great. Now slowly bring the temp up and see where it turns off. It turned off at 248.
Bring temp down again and it turns on at 237.
So it seems the circuit as shown WILL work with a variance of 10 to 15 degrees!!
I still want to strap the comparator on the front end to tighten it up a bit. Hopefully I can do that today.
-rob
RobM (YankeeRob)
TVWBB Super Fan
Joe,
This circuit is pretty easy to build. Really the only trick is mounting the fan on your smoker so it doesn't melt.
If you do go the commercial route get a Stoker rather then a Guru. They cost the same but the stoker is programmable with software supported on this web site. You could even set up a stoker such that you could control your smoke from any computer on the internet. Many of us have.
-rob
This circuit is pretty easy to build. Really the only trick is mounting the fan on your smoker so it doesn't melt.
If you do go the commercial route get a Stoker rather then a Guru. They cost the same but the stoker is programmable with software supported on this web site. You could even set up a stoker such that you could control your smoke from any computer on the internet. Many of us have.
-rob
RobM (YankeeRob)
TVWBB Super Fan
Joe,
It's a pretty simple circuit. Almost the same thing that controls your home heating for the most part. I worked on it today.
I think I will drop the thermistor because it became open when too much heat was applied. I am going to try and find a replacable probe and use that instead. The probe is like ~$10.
I will feed the probe voltage into a ref voltage and slam on/off a fan.... Total parts less than $20. If you want put it in a kit maybe $30 but that will include the probe, parts box, fan, fan mount and connections to it. Stay tuned to this thread as I have made some good progress this weekend
-rob
It's a pretty simple circuit. Almost the same thing that controls your home heating for the most part. I worked on it today.
I think I will drop the thermistor because it became open when too much heat was applied. I am going to try and find a replacable probe and use that instead. The probe is like ~$10.
I will feed the probe voltage into a ref voltage and slam on/off a fan.... Total parts less than $20. If you want put it in a kit maybe $30 but that will include the probe, parts box, fan, fan mount and connections to it. Stay tuned to this thread as I have made some good progress this weekend
-rob
Joe,
Ideally, my intent was to keep SCATS under $20. If we find the right thermistor and fan, this solution should be very usable. We will definitely post the part numbers and where to get everything once we have solidified the design. Interchanging thermistors would also be an option if you wanted to change temp ranges.
Rob,
I thought these thermistors were advertised as current limiting when it got too hot? Seems like the therm should have remained open once the temperature passes a certain threshold.
-mark
Ideally, my intent was to keep SCATS under $20. If we find the right thermistor and fan, this solution should be very usable. We will definitely post the part numbers and where to get everything once we have solidified the design. Interchanging thermistors would also be an option if you wanted to change temp ranges.
Rob,
I thought these thermistors were advertised as current limiting when it got too hot? Seems like the therm should have remained open once the temperature passes a certain threshold.
-mark
I know the blower used for the Stoker is a 5 volt fan. It would be really cool if this circuit and blower could be setup to run off a 9 volt battery. If so, that blower housing could "house" the blower, circuit and 9 volt battery. Having a single wire to the probe would really make this a simple setup. Thoughts?
9 volt batteries are not a good choice for applications like this. They have high internal resistance and as such, should only be used in very low current applications. They also have poor capacity. Combine these with cold weather and they likely won't last long enough for a cook.
johnbrisbin
TVWBB Member
Originally posted by A. Vale:
I know the blower used for the Stoker is a 5 volt fan. It would be really cool if this circuit and blower could be setup to run off a 9 volt battery. If so, that blower housing could "house" the blower, circuit and 9 volt battery. Having a single wire to the probe would really make this a simple setup. Thoughts?
Most common fans are either 12VDC or 120VAC. The Stoker fans at 5VDC are a rarity and reduce the choices available (but they make the wiring and circuity simple).
While modern circuits can run for months or even years on a small battery, any blower worthy of the name will consume far more power than a 9V battery can deliver because it does real work (in the physics sense). The battery would be exhausted in minutes with even a small 5CFM blower.
A larger, deep-discharge battery could work but since you are looking for 8 to 16 hours for a brisket smoke the battery will probably be too large to attach to the fan mounting. The proximity to heat, the awkward angles of mounting in some smokers and the limited support strength of the blower to smoker adapters available from current vendors all combine to force separation of the battery (if such is used) from the blower and the smoker.
Battery power is a useful option, but most of the time it is more convenient to plug in a wall wart into an extension cord. Other times a battery is necessary.
If you choose a 12V system, you can power the system directly from a car battery or similar or a readily available 12VDC adapter and you have a much broader (read cheaper) choice of fans.
You can reduce the wiring by putting the required circuitry on the fan, but the heat will tend to reduce reliability of that circuitry. Since putting the circuitry at the sensor is worse, the usual choice will be to use more wire and co-locate the whatever circuitry is required (comparators to sharpen the response and allow adjustment, for example) with the power supply.
Wire is cheap compared to the alternatives.
RobM (YankeeRob)
TVWBB Super Fan
Some thoughts on these most recent posts:
The thermistors we got from ebay I think are too fragile to be in an oven that can go up to 350 degrees. When my heat gun came too close and the temp went up to 300 it shorted. We need something more durable and I have found this here:
http://www.comforthouse.com/pol362reppro.html
For $10 it's a Polder replacement probe. In our application you will need a reference thermometer to know where to set the motor stop point. This could be your smoker thermometer or something else. You could get the complete Polder device and use that to bring your pit to temp. Then unplug the probe and stick into into the fan controller. I purchased the Polder unit and 2 spare probes yesterday.
If these probes are like my other kitchen probes they are NTC so at room temp they are 300K and 350 about 3K. This is not a problem using an op amp comparator on the front end. I found an op amp at the Shack for $1 that can do this. The op amp looks at the voltage of the probe (created by voltage divider) on the non-inverting input and compares that to a reference voltage set by a pot on the inverting input. The output of the op amp drives the MOSFET transistor and thereby the fan. The circuit works in an ON/OFF fashion and gets rid of the current breakover issue.
Fans and voltages
Stoker blowers have a chip in the 1/4 inch plug that I think will be destroyed at 12 volts. Granted you could snip the wires but the blower is expensive. I build my own PC's and therefore have a couple of old CPU fans lying about. Since I'm going to strap this unit on a BGE I'm pretty sure I wont need more than that. If you need to you should be able to swap out any fan you need because the circuit I describe does a hard ON/OFF so a larger fan with higher breakover current should not matter.
Voltages: I am using a 12 volt brick. I like 12 volts because I want this unit to be a backup so if I'm at a contest and the power fails I can run this from my truck battery.
The power supply voltage for the sensing circuit is 12 volts but the motor drive voltage can be totally separate if you need it to be.
OK then so far for the circuit the component list is like this.
1 NTC replacement probe
1 resistor for probe voltage divider
1 100k multi-turn pot (ref voltage divider)
1 op amp
1 op amp output resistor to feed gate of MOSFET
1 MOSFET
1 CPU fan
12 volt brick (from my Guru)
if you want to throw on a "Fan On" indicator
1 2.2K resistor
1 green LED
I also found a piece of stove pipe that seems would be perfect for a BGE mount. Once I get the electronics working I'll worry about fan mounts.
-rob
The thermistors we got from ebay I think are too fragile to be in an oven that can go up to 350 degrees. When my heat gun came too close and the temp went up to 300 it shorted. We need something more durable and I have found this here:
http://www.comforthouse.com/pol362reppro.html
For $10 it's a Polder replacement probe. In our application you will need a reference thermometer to know where to set the motor stop point. This could be your smoker thermometer or something else. You could get the complete Polder device and use that to bring your pit to temp. Then unplug the probe and stick into into the fan controller. I purchased the Polder unit and 2 spare probes yesterday.
If these probes are like my other kitchen probes they are NTC so at room temp they are 300K and 350 about 3K. This is not a problem using an op amp comparator on the front end. I found an op amp at the Shack for $1 that can do this. The op amp looks at the voltage of the probe (created by voltage divider) on the non-inverting input and compares that to a reference voltage set by a pot on the inverting input. The output of the op amp drives the MOSFET transistor and thereby the fan. The circuit works in an ON/OFF fashion and gets rid of the current breakover issue.
Fans and voltages
Stoker blowers have a chip in the 1/4 inch plug that I think will be destroyed at 12 volts. Granted you could snip the wires but the blower is expensive. I build my own PC's and therefore have a couple of old CPU fans lying about. Since I'm going to strap this unit on a BGE I'm pretty sure I wont need more than that. If you need to you should be able to swap out any fan you need because the circuit I describe does a hard ON/OFF so a larger fan with higher breakover current should not matter.
Voltages: I am using a 12 volt brick. I like 12 volts because I want this unit to be a backup so if I'm at a contest and the power fails I can run this from my truck battery.
The power supply voltage for the sensing circuit is 12 volts but the motor drive voltage can be totally separate if you need it to be.
OK then so far for the circuit the component list is like this.
1 NTC replacement probe
1 resistor for probe voltage divider
1 100k multi-turn pot (ref voltage divider)
1 op amp
1 op amp output resistor to feed gate of MOSFET
1 MOSFET
1 CPU fan
12 volt brick (from my Guru)
if you want to throw on a "Fan On" indicator
1 2.2K resistor
1 green LED
I also found a piece of stove pipe that seems would be perfect for a BGE mount. Once I get the electronics working I'll worry about fan mounts.
-rob
RobM (YankeeRob)
TVWBB Super Fan
SUCCESS!!!
After several failed attempts (NEVER use a 741 as an comparator!) I finally got this thing working. The fan turns on/off at nearly the exact same voltage (or temp) every time! Some changes:
- I'm using a LM339 comparator instead of 741 op amp
- I blew up my 12 volt brick so I found an 18 volt laptop brick instead. I added a 12 volt regulator to the circuit for the sensing part. The motor connect right up the 18 volts for max CFM.
- I added a "Fan On" LED.
So the parts list is now:
Polder replacement probe
4 resistors
1 10K pot
1 LED
LM339 comparator
MOSFET
12 volt regulator
CPU fan
Of course you'll want a project box, perf board and connectors for your probe, fan and DC power. Note that ALL of these items can be found at Radio Shack. In addition you can use and DC power supply (brick) from 12 to 24 (I think) volts because of the 12volt regulator. I'll bet everyone has an old brick laying about suitable for the task.
All my wiring is on breadboard right now so the next task is to get it on perfboard and mounted in a project box. Then I need to mount the fan for a BGE test burn.
I'll take pics as I build it. Hopefully I can get it done this weekend.
-rob
After several failed attempts (NEVER use a 741 as an comparator!) I finally got this thing working. The fan turns on/off at nearly the exact same voltage (or temp) every time! Some changes:
- I'm using a LM339 comparator instead of 741 op amp
- I blew up my 12 volt brick so I found an 18 volt laptop brick instead. I added a 12 volt regulator to the circuit for the sensing part. The motor connect right up the 18 volts for max CFM.
- I added a "Fan On" LED.
So the parts list is now:
Polder replacement probe
4 resistors
1 10K pot
1 LED
LM339 comparator
MOSFET
12 volt regulator
CPU fan
Of course you'll want a project box, perf board and connectors for your probe, fan and DC power. Note that ALL of these items can be found at Radio Shack. In addition you can use and DC power supply (brick) from 12 to 24 (I think) volts because of the 12volt regulator. I'll bet everyone has an old brick laying about suitable for the task.
All my wiring is on breadboard right now so the next task is to get it on perfboard and mounted in a project box. Then I need to mount the fan for a BGE test burn.
I'll take pics as I build it. Hopefully I can get it done this weekend.
-rob
Rob,
This is great news! Even though I own a Stoker and a BBQ Guru I really want to build one of these as it sounds like a lot of fun. I'll have to follow your lead for the circuit but have a lot of ideas on how to package the blower and circuit into a single package. When do you think you will have time to list the electronic components (ideally Radio Shack part numbers too) and show a picture of the circuit or an updated diagram?
This is great news! Even though I own a Stoker and a BBQ Guru I really want to build one of these as it sounds like a lot of fun. I'll have to follow your lead for the circuit but have a lot of ideas on how to package the blower and circuit into a single package. When do you think you will have time to list the electronic components (ideally Radio Shack part numbers too) and show a picture of the circuit or an updated diagram?
RobM (YankeeRob)
TVWBB Super Fan
OK, My Polder probe actually came in Friday. Up to that point I was using a different one. Good news is they are identical in thermal terms. I tested out my circuit with a heat gun. once it's set to a temp just blowing on the probe will cause the fan to turn on until the heat gun gets it back to temp.
Anyway, I thought that this might generate alot of responses so I started a new thread here:
http://tvwbb.infopop.cc/eve/forums/a/tpc/f/9270072103/m/5980036295
Anyway, I thought that this might generate alot of responses so I started a new thread here:
http://tvwbb.infopop.cc/eve/forums/a/tpc/f/9270072103/m/5980036295