Hey guys,

Can anyone help me?
I am trying to create a low heating circuit prefered about human body temperature(37-40 degree celsius).

The application is bascially using it to heat up a wire mesh via conduction which will be used to attract and kill mosquitoes

So far I have tried researching and most websites suggest induction heating but they are of very high tempertures which is not what I require.

 

I think the secret will be to use a closed loop system, so it senses the heat and adjusts the power to keep the heat at the correct temperature.

I would try a LM35 or LM34 temeprature sensor which makes a simple DC voltage in resonse to the sensed temperature, then a comparator oscillator oscillating around that setpoint which gives the required PWM to maintain temperature.

It might sound complicated but is a fairly simple circuit.

The main issues are on the high power side. Have you decided on a power supply, heating element(s) and how to switch the power?

 

I maybe wrong here, but I've read and always assumed that the main attraction of mosquitoes to humans/animals is CO2. Not heat. The existing mosquito killers use burning of propane or similar gases to generate the CO2, heat is just a byproduct.

 

I think the secret will be to use a closed loop system, so it senses the heat and adjusts the power to keep the heat at the correct temperature.

I would try a LM35 or LM34 temeprature sensor which makes a simple DC voltage in resonse to the sensed temperature, then a comparator oscillator oscillating around that setpoint which gives the required PWM to maintain temperature.

It might sound complicated but is a fairly simple circuit.

The main issues are on the high power side. Have you decided on a power supply, heating element(s) and how to switch the power?

I am looking at maybe a 9volt battery, the problem now is i dont know if I should use a induction circuit.
Here is a link of the induction circuit maybe i can change the value of the components but do you think it can work RB?
http://www.rmcybernetics.com/projects/DIY_Devices/diy-induction-heater.htm

 

I maybe wrong here, but I've read and always assumed that the main attraction of mosquitoes to humans/animals is CO2. Not heat. The existing mosquito killers use burning of propane or similar gases to generate the CO2, heat is just a byproduct.

Hey shortbus yepp, they are attracted by CO2 moist and heat I have the CO2 and moist part covered did a few experiements and realise that they are still not attracted. I soon discovered that they also take heat into consideration.

 

I am looking at maybe a 9volt battery

If you mean the small 9V "transistor" battery, I think you'll be disappointed. There just isn't much energy stored in that small package. Making heat requires energy. Heat IS energy.

BTW, I agree with the approach suggested by RB. That's what I'd do.

If anyone ever cracks the code why mosquito attraction is mostly genetic, we can stop messing around with UV light, heat and CO2. Things like uric acid, lactic acid and even cholesterol in the skin correlate to mosquito attraction, but I'm not sure anyone is suggesting it's cause-and-effect yet.

 

How big is the mesh cylinder shown? If it's several inches in diameter you may need a few Watts of power to keep it at the right temperature (depending on ambient temperature). Wayneh's right; a 9V battery (PP3) won't do the job.

 

I maybe wrong here, but I've read and always assumed that the main attraction of mosquitoes to humans/animals is CO2. Not heat. The existing mosquito killers use burning of propane or similar gases to generate the CO2, heat is just a byproduct.

Not arguing with the CO2, but they do see body heat and can clearly see your veins under the skin, seeing where they are closest to the skin from the IR glow of the vein shining out of the skin. I saw it on a science show.

Glowing bug zappers attract mozzies very well too, either they like the HF flickering blue light or just the fact that the thing is nice and warm.

 

How big is the mesh cylinder shown?

Its about 13cm in diameter.

What if i can connect 2 9v batteries in series making it 18v would that help? Or do I need a step up transformer?

I tried UV lights, I did a bit of literature research and found out that Mozzies also like certain colours and hate certain colours thats why they are not so fond of UV lights (just a thoery).

The problem now is how do i come out with a circuit for this usage

 

Maybe draw some veins with a crayon and shine an IR LED on it.

 

Its about 13cm in diameter.

What if i can connect 2 9v batteries in series making it 18v would that help? Or do I need a step up transformer?
...

That thing will radiate (lose) all its heat really well. You are going to need quite a bit of wattage to keep it at 37'C especially at night in the open air where there are drafts etc. I'm thinking 10W to 20W for heating depending on ambient temps and drafts?

It will need to be mains powered (to get enough watts for the heating) through a step-down transformer. That's all for the wire frame heating, the "zapper" part will be extra.

 

Can you not use an heater in the centre of your mesh at the desired temp, and put a high voltage on the mesh like the fly zappers use to kill the mossys.

 

Can you not use an heater in the centre of your mesh at the desired temp, and put a high voltage on the mesh like the fly zappers use to kill the mossys.

Would'nt it be dangerous as it is exposed. The mesh will be expose to allow people to carry it. I tried applying direct voltage onto it, it created a 2A current flow which is super dangerous.

@RB I guess I would have to scrape this idea? We were thinking of making it battery operated

 

If you really need to heat that heavy mesh- you will need some watts to do it.

You could pass a heavy current through the mesh, at a very low voltage.
The simplest way would be to connect some heavy copper bus bars to each end of the mesh, connect them to the output terminals of a soldering gun.

A soldering gun is just a small transformer with a shorted secondary (soldering tip), which gets hot from the massive current flow.

The mesh is much larger and has a much higher resistance, so it will not heat up as much as the tip does.


The transformer provides electrical isolation, so it's safe, the output voltage is very low.

You could regulate the temperature using a sensor and a simple on/off controller to hold the desired temperature

 

.... but if it must be battery-powered and portable then you'll need strong arm muscles; the battery will be large and heavy .

 

Maybe a change of approach? If the heater is just to make the right "colour" of IR light, then in can be enclosed within a clear container.

That insulates it from heat loss and the power consumption goes right down.

As a good example of an insulated container, try an incandescent light bulb. You can get a small 12v bulb and run it at regulated current/voltage with PWM, so the filament JUST gets warm.

I'm not sure how you would measure the temperature but you could try a non contact IR thermometer. In the worst case that the thermometer measures the glass and not the filament maybe you could just control it so the glass is at 37'C?

I wonder what the mozzie sees? The glass or the filament?