Ok, so in beekeeping, treatments have to be performed for a little pest known as the varroa mite. One of the most common treatments is to apply an oxcalic acid vapor. There are multiple approaches to convert the oxalic acid powder into vapor (all by using heat) but I have an idea for a more efficient design.
General description: A crucible containing the powdered acid will be heated with a couple heating elements. Once a known vaporization temperature point is reached, a small blower will turn on blowing air through a pathway in the crucible out a tip and into the bee hive. The heating elements will cycle to maintain a specific temperature range as overheating the acid powder can cause an adverse reaction that is not beneficial to the bees.
Expect that I will want to control 2 or 3 external relays from the board and power 2 to 4 LED's to show status. I also need to read a K-type thermocouple which I expect to run through a basic amplifier board. If I get fancy, I may want to add a low cost led or lcd display but if that drives the cost of the board to a higher price point, I will probably scrap that idea.
Cost is a factor as I need to keep the overall cost down and materials are already running a little higher than I would like. I had also explored using temperature driven snap switches like what is used in the HVAC field but that is much less flexible when it comes to temperature control as they are preset to fixed values and it's difficult to find the exact set points needed.
I will have a more detailed design chart that I can upload when I get more into the nitty gritty but my initial question is, what specific board would be the most suitable for this type of control ?
If cost is a factor before you even know if your project will work, then you have two goals at cross purposes. Get your project to work perfectly, then try to reduce costs.
I am using known working methods for each of the functions of the whole unit so proving the system to work is really not needed. What I am doing is combining a few functions of working designs and controlling them with more efficient use of power.
The temperature range I am planning on working with is around 280 F (137 C) to 350 F (176 C). I am using a pair of automotive glow plugs in a small aluminum crucible. This is a common design in more simple oxcalic acid vaporizers.
I am using a small computer blower type fan to blow the vapor into the hive. I will use a potentiometer to control the desired air flow. Both the heating glow plugs and the fan will be operated using separate relays which only need 5vdc for coil activation. The relay contacts are rated for well more than the voltage / current they will be seeing.
They system input voltage will be a 12vdc volt lithium power pack. (Alternatively, if I was to use this on a large bee yard with many hives, I could use a 12 volt inverter). Both the glow plugs and the fan are rated for 12 vdc. My little bit of research makes me believe that the arduino boards can handle an input voltage of 5-12vdc but if that is not accurate, I will need to add a voltage ctrl (regulator, transformer, etc.).
Yes, outdoors as I am treating honeybee hives. Using oxcalic acid, especially when vaporizing it, requires proper PPE including a respirator with filters rated for organic acid vapors.
Oxcalic acid is a natural compound found in many plants that bees collect nectar from and is actually a minor component in true honey. However, it is not in a form that deters the varroa mites. By injecting a vapor into the hive, it condenses onto the comb and onto the bees themselves (does not harm them) but causes the varroa mites to not be able to stay attached to the bees and they drop to the bottom and die.
One additional note, I already have an UNO R4 WiFi that I am working with for a separate project but can use this while build my unit to start with but that will be temporary so and looking for a more basic board that covers just what I need for this project. The UNO R4 has more capability than needed so I expect to be able to go to a lower cost board.
Was wondering the same about current draw. Glow plugs can draw quite a lot of current, particularly from cold, which will have a significant bearing on the power source to be used.
Any arduino will do the job. If it were not for your comment about cost being important, I’d choose one of the models with an onboard display, like a LilyGo HMI or an M5Stack unit.
But if you want a simple display and keeping it cheap, then an I2C LCD and an Arduino Nano will be fine.
What’s the vaporization temp?
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Ok, I see you added temp in one of your replies. At 350F you’re entering thermocouple territory, but you might also be able to find a thermistor in that range. @hammy is right that you could probably find an off the shelf temperature controller for less than it costs to build one.
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Strange that you have not given the current requirements for any of your components.
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I don't have the exact current draw of the glow plugs but the blower fan is 1.8 watts at 12vdc. I actually picked up the glow plugs today and will test tomorrow on their current draw.
I'm confused though as to why that would impact which arduino board would be the best fit for this project. I can swap out my power source as needed to provide the required wattage for the glow plugs. A lot of the current vaporizer designs just connect straight to a 12vdc source with no controls and depend on an arbitrary time to complete the vaporization process with no control of temperature. By controlling the temp and cycling the glow plugs as needed, I will reduce the overall power consumption.
Another comment above mentioned looking at commercial temperature controllers but my thoughts are they are all going to require 120 VAC. I'll still take a quick look but not counting on that option.
I have an initial cost estimate for the entire control circuit of $84.00 USD
Arduino UNO R3 $30
Thermocouple $10
T-Couple Amp $10
Relays $8
A couple toggles switches $16
A couple LED's $10
I don't include the blower or glow plugs as they are used independent of the control circuit and would be needed even without controlling the temp.
My very quick look indicates one of the NANO boards could work but I'm not positive which is why I'm posting the question.
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Any arduino will do the job. If it were not for your comment about cost being important, I’d choose one of the models with an onboard display, like a LilyGo HMI or an M5Stack unit.
But if you want a simple display and keeping it cheap, then an I2C LCD and an Arduino Nano will be fine.
What’s the vaporization temp?
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Ok, I see you added temp in one of your replies. At 350F you’re entering thermocouple territory, but you might also be able to find a thermistor in that range. @hammy is right that you could probably find an off the shelf temperature controller for less than it costs to build one.
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I saw the comment about the off the shelf controller but I have yet to find one that isn't powered by 120 VAC. The environment for treating bees rarely if ever has household power available as most be yards, mine included, is not near a residence.
I can look at thermistors but am less familiar with them than thermocouples. I have selected a thermocouple that is used with rapid proto machines that will basically screw into a small tapped hole in my crucible which makes for super easy mounting.
What Diesel engine are they for? My personal experience with glow plugs and Diesel engines are they are very current intense and can be cycled for 10-15 seconds and then off for a lot more seconds. Some were 6 volt units, but run at 12 volts for a short time. All needed replacement after 1-2 years. Modern diesels use a glowing/hot screen in the air stream and they will last for ever. The best glow plugs are in my Kubota tractor.
Go with the classic Nano (ATmega328), it's cheap and widely supported, like Uno R3 in smaller packet.
To keep your budget tight, you could source your components from somewhere else if actual supplier asks $26 for couple of LEDs and switches...
Is this personal or commercial?
Either way, I would agree with the others who mentioned commercial controllers.
There shouldn't be a problem in finding one that can operate at low voltages.
Oxalic acid isn't to be messed with, as you probably know. It's a regulated substance under the UK Poisons Act and elsewhere.
It's not in the same league as cyanide, but still needs to be treated with respect.
Funnily enough, I was after some for wood bleaching after restoring vintage sewing machine cases.
Despite the regulations, it easy to obtain in pure solid form, from suppliers to beekeepers. No evidence of occupation required. My main worry would be keeping good control of the temperature.
Going beyond the vaporisation temperature could go into pyrolysis territory with hazardous results.
I'll search more but have not found an off the shelf controller that is powered at 12vdc as of yet. This is for personal use though because of how some of the raw materials are available, I may fabricate 2 or 3. The aluminum for the main crucible would be a length that would produce three units for instance.
Yes, oxcalic acid is nasty. As I stated above, it requires adequate PPE including a respirator rated for organic acid vapor.
Typically, each treatment used between 3 and 5 grams and even using an uncontrolled device, the powder generally vaporizes before it has a chance to reach critical temperatures. I'm just looking for better control so that I can treat multiple hives in less time and not worry about my crucible being too hot when I add the powder for each treatment. With an uncontrolled device, I have to let the crucible cool a bit between treatments.
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Go with the classic Nano (ATmega328), it's cheap and widely supported, like Uno R3 in smaller packet.
To keep your budget tight, you could source your components from somewhere else if actual supplier asks $26 for couple of LEDs and switches...
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I'll check that model out. Was having a hard time comparing all the different Nano versions.
The cost I put for switches and led's was a rough number pulling from amazon but when I make the actual purchases, I always price shop.
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What Diesel engine are they for? My personal experience with glow plugs and Diesel engines are they are very current intense and can be cycled for 10-15 seconds and then off for a lot more seconds. Some were 6 volt units, but run at 12 volts for a short time. All needed replacement after 1-2 years. Modern diesels use a glowing/hot screen in the air stream and they will last for ever. The best glow plugs are in my Kubota tractor.
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The actual glow plugs are NGK 2031 / Y-103V and are used in small 2 and three cylinder diesels such as tractors. This particular glow plug is the same one that is in a basic ox/acid vaporizer that is available commercially that is powered by a 12vdc auto battery for 5 minutes at a time. The one I have has been used for many years without problems. It's a low cost glow plug that appears pretty robust. I did look into other types of surface mount and insertion heaters but the costs were much greater.