system for monitoring and controlling temperature in two infant incubators

[peeryus]

Hi all

My project is a system for monitoring & controlling temperature in 2 incubators using a GUI. My 1st question ( of many in the near future) to the experts is, what heater can I use. I want a low voltage heater, preferably 5V/12V. I can't seem to find anything. The dimensions of the incubator are 45cm x 30cm x 20cm.

Please help

Thanks

 

[ericgibbs]

Hi all

My project is a system for monitoring & controlling temperature in 2 incubators using a GUI. My 1st question ( of many in the near future) to the experts is, what heater can I use. I want a low voltage heater, preferably 5V/12V. I can't seem to find anything. The dimensions of the incubator are 45cm x 30cm x 20cm.

Please help

Thanks

hi,
The vehicle range of 12v is available. Are these human infants.??
portable 12v heaters - Google Search

 

[peeryus]

Thanks for the quick reply

Yeah human infants but it's not going to be really used in the field. Just for my project purposes. A requirement of my system is that there needs to be a fan and heater connected in the incubator separately and the GUI must display if the fan and heater are on/off. The user must also be able to switch the fan or heater on/off using the GUI. I think the demisters come with a fan and heater though :-( Any other ideas? I'll keep looking.

Thanks

 

[Reloadron]

Thanks for the quick reply

Yeah human infants but it's not going to be really used in the field. Just for my project purposes. A requirement of my system is that there needs to be a fan and heater connected in the incubator separately and the GUI must display if the fan and heater are on/off. The user must also be able to switch the fan or heater on/off using the GUI. I think the demisters come with a fan and heater though :-( Any other ideas? I'll keep looking.

Thanks

OK, so you don't need a mountain of safety features? When you say GUI (Graphic User Interface) do you mean as in using a computer for control and control software driven?

Ron

 

[peeryus]

Yeah I'm going to use Visual Basic for the GUI. Basic block diagram is, GUI -------> Microcontroller -------> Incubator. No serious safety features. To warm the incubator, I want to use a heater and a fan to spread the heat evenly. I'm looking for a simple 5V/12V heater. Also, any idea what power the heater should be able to deliver to warm up the incubator (dimensions given above) reasonably easily.

Peer

 

[Reloadron]

What you have is a box with a volume of about 27,000 Cubic Centimeters. You could get into the watt density and this link may help. Also, you aren't looking at much heat. I would guess maybe a little above 34 or 36 degrees C. to maintain the box at.

The trick becomes finding a heater element for air that is a small low voltage element. Maybe a small finned strip element or small duct heater? I haven't had much luck looking.

OK on using VB to make your form and GUI. That should work out well. You can interface with a PIC or any number of data acquisition or data I/O devices for measurement and control. If you want to be slick you could use a basic 3 wire el cheapo computer fan and measure the tach out (two pulses per revolution) for a fan failure and fan speed detector.

The problem is finding a suitable low voltage heater for air. Worst case you could likely throttle one of the 12 volt automotive heaters I have seen online. Again, you don't need much heat.

Ron

 

[peeryus]

Thanks for the replies

I worked it out as follows :

@ 20°C : density = 1.2041 kg/m^3

Therefore mass = (1.2041 kg/m^3) x (0.027 m^3) = 0.0325kg

Q = m x C x (delta T)
= (0.0325kg) x (1.005 kJ/kg K) x (294K - 293K)
= 0.0327 kJ
= 32.7 J
= 0.009 Watt-hour

So would I be correct in saying that I need 0.54W if I want to increase the temperature by 1 degree in 1 minute?

 

[Reloadron]

That sounds correct. The basic problem is finding a heater. Fabricating your own isn't out of the question but a nice little 12 volt air heater would be nice. Have you found anything?

Ron

 

[peeryus]

Hi Ron

I've been looking everywhere but can't seem to find anything. Even if it runs off 24V I won't mind. I'll just use a transistor to drive it. But I want to stay away from AC mains. I'll keep looking though. I'm using this fan.
(SUNON | KDE0504PFV1.11.MS.A.GN | KDE Series High Speed 40 mm 8 CFM 5 VDC Vapo Bearing Maglev Motor Fan - Future Electronics)
Nice and small and the highest CFM and rpm that I've come across and it needs 5VDC.

Peer

 

[Diver300]

You can just have transistor on a heat sink as the heater. You need a current limit, and this circuit:-

**broken link removed** works fine. If the transistor is the heater, the load resistor (but not the current limit one) will be zero.

 

[peeryus]

It's for an honours degree. I want to keep everything DC powered. My supervisor has allowed me to use a halogen bulb instead of a heater as I could not find a heater. This makes life abit easier.

Anyways, I've attached my code to test the circuit for the fan operation. I'm using a transistor to drive the fan. The transistor is turned on when portB.0 goes high in the "equal" routine. I'm using an stk500 to program the micro. It works fine but once the fan comes on on the first time portB.0 goes high, it doesn't stop for maybe 20seconds. What could be causing this?

.include "8515def.inc"

.org 0x0000
	rjmp main

.def output = R16

main:
	
	ldi r16, low(RAMEND)
	out SPL, r16
	ldi r16, high(RAMEND)
	out SPH, r16

	LDI output, $FF
	OUT DDRB, output ; making as o/p

	LDI output, $00
	OUT DDRD, output ; making as i/p

	LDI output, $FF
	OUT portD, output ; enable pullup resistor

	LDI output, $00
	out portB, output ; put all led's on
	
	in r17, pinD
	cpi r17, 254
	breq equal
	
	rjmp main

equal:
	
	sbi portB, 0

**broken link removed**

Thanks

 

[Boncuk]

I do not recommend to use anything as heater which involves a heat sink.

Any heat sink will result in accumulative heating, meaning the heat sink will still radiate heat with the heater switched off - resulting in high temperature overshoot.

Instead I suggest to use high power resistors (available from 5 to 17W (and 0.082Ω to 15KΩ for 5W types)) with ceramic body.

Arrange a few of them directly on the fan pressure side. Using resistors for heating each resistor should not dissipate more than 50% of its rated power (better 40%).

Calculate the number and value of the resistor assembly to have them heated slightly above the highest desired temperature for optimum accuracy and least overshoot.

The software should be able to recognize tendencies and react accordingly - PWMing the heaters.

Boncuk

 

[peeryus]

I see what you are saying Boncuk and value your advice. The thing is that in a real incubator, resistors aren't used to warm the incubator. A bulb or even a heater are used. Any ideas what I'm doing wrong in the code? :-(

 

[peeryus]

Hey guys

I'm using an STK500.I'm trying to get my ADC code for my temperature sensor working but I'm having a problem programming the chip(ATmega16). I get this error (shown below) when trying to program using AVR Studio. My ISP frequency = 57kHz and clock frequency = 3.6MHz

**broken link removed**

And when trying to program the micro from CodeVisionAVR, it cant detect the STK500.

What am I doing wrong?

 

[peeryus]

Just an update........

Ok so I got the ADC to work for two separate Lm35's. I am using two LM35's and can display the corresponding temperatures on an LCD and switch the fan on when the temp goes to a max value and switch the heater on when the temp goes to a min value (for now I've just used LED's to simulate the switching of the fan/heater). Now I need to create a VB app that'll display each temp & the status of each fan/heater. Its the 1st time I'm using VB for something like this. Can someone help me learn how to use this or provide a link/tutorial that'll assist me?

Thanks in advance