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Question: How to build a soft circuit for controlling heat applied to heat-sensitive ink
circuit for heat-sensitive ink - 2 (50%)
heat controlling circuit + heat-sensitive ink + arduino pro mini - 2 (50%)
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Author Topic: circuit for heat controlling with Arduino  (Read 2068 times)
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Dear all,

I’m looking for ways to generate and control heat for an electronic t-shirt project controlled with Arduino pro mini. The shirt will have multiple parts painted with Thermochromic (heat-sensitive) ink. Each painted area changes its colour every time the Arduino applies heat to it, via a heating element using conductive thread from Sparkfun (234/34 4ply www.sparkfun.com/products/8549).

Recently, I found a schematic (see below) at www.kobakant.at/DIY/?p=2909 but not sure that the heat released from MOSFET is over maximum heat the conductive thread can take.

Anyone has ideas on this or know how to modify the circuit, please let me know.

Thanks.


* heatGenerateSoftCircuit+plan_2.jpg (139 KB, 640x264 - viewed 30 times.)

* HeatControllDriver_Schematic_kobakant.at.png (48.58 KB, 578x418 - viewed 54 times.)
« Last Edit: April 05, 2011, 12:49:43 pm by sawadeejar » Logged

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but not sure that the heat released from MOSFET is over maximum heat the conductive thread can take.
You are mixing up two totally different things. The heat produced by the heater is not the same as the heat generated by the controlling circuit.
Those circuits will not do what you want (there rubbish actually).
You just need a logic level FET and a good power supply. Heaters take a lot of current, is that available?
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Hi Grumpy_Mike,

Thank you for your reply.

Does this N-channel MOSFET IRFP450A 14A 500V (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=MOSFET+IRLML+0030&x=0&y=0) good enough to go with 12v or 24v battery supply?
« Last Edit: April 05, 2011, 04:26:17 pm by sawadeejar » Logged

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No you need a FET that will turn on with 5v, the gate threshold is just the point it starts to turn not when it is fully turned on.
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... Each painted area changes its colour every time the Arduino applies heat to it...
Arduinos use low or pico power processors. They only can apply voltages and if there is a resistor (electrical heaters are mostly resistors) this voltages can cause a current flow. The product of both is the power (P=U*I).
While the max. current from an Arduino pin can be approx. 30-40mA (depending on resistor value) you can assume a power about 200mW. This can only heat a very small area.

If you put much more power to that T-shirt, you risk burning it or yourself!

Take care of that!
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While the max. current from an Arduino pin can be approx. 30-40mA (depending on resistor value) you can assume a power about 200mW
Yes we know that's why we are talking about driving a FET to do the current switching.
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Can you please give me a hint on how to put all these parts together?

Thank you
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Look at this:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html
Any load is the same so when you see motor say heating element.

You can use a FET, gate connected through a 100R or so resistor source to ground, drain to heating element, other end of heating element to 12 or 24 volts. Providing that the FET will fully switch on 5V. Something like the IRFZ44. There is no need for that complementary driver you had before.
EDIT - please note this is IRFZ44 not IRFZ44E, or IRFZ44P, however the IRFZ44N will also just about be OK at 5V

The heat dissipated by the FET will be the current squared times the Ron resistance of the FET.
The heat generated by the heater will be the current squared times the resistance of the heating element.
As the Ron for a FET is very small there is much less heat generated inside the FET than the heater.

For further considerations see:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html
« Last Edit: May 03, 2011, 08:20:04 am by Grumpy_Mike » Logged

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The links are very helpful. I'm waiting for the parts to arrive. I'll get back soon.
Thank you.
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Hi,

I've just received all part and quickly wired them like this:
FET Gate --- 100Ω --- Arduino D5
FET Drain --- Heating Element --- 12v +
FET Source --- Gnd

A picture is also attached.

The problem i have so far is after providing full 5v to the FET Gate for a while, the heating element is not heated up. The part that is completely hot is the FET itself. Is there anything wrong in my wiring?





 


* IMAG0382.jpg (482.28 KB, 1280x960 - viewed 45 times.)
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Hi,

I've just received all part and quickly wired them like this:
FET Gate --- 100Ω --- Arduino D5
FET Drain --- Heating Element --- 12v +
FET Source --- Gnd

A picture is also attached.

The problem i have so far is after providing full 5v to the FET Gate for a while, the heating element is not heated up. The part that is completely hot is the FET itself. Is there anything wrong in my wiring?





 

Can you clearly state what type of mosfet you are trying to use? The drawing says IRFZ44 which is not a LOGIC LEVEL mosfet and will not turn on fully with a arduino digital output. You have been told repeatably that you need to use a logic level mosfet.

Lefty
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Can you clearly state what type of mosfet you are trying to use? The drawing says IRFZ44 which is not a LOGIC LEVEL mosfet and will not turn on fully with a arduino digital output. You have been told repeatably that you need to use a logic level mosfet.

Thank you for the reply.

I'm using IRFZ44E as kindly mentioned by Grumpy_mike.
I don't know how to check if a mosfet is a Logic Level one.
However, in the datasheet www.irf.com/product-info/datasheets/data/irfz44e.pdf (page 7) it's said something like "VGS = 5V for Logic Level Devices" so i assumed it was OK to use.

Can you please point me to one or two that can replace the IRFZ44?
Searching on google i found some tutorials using IRF630 and BS170. Are these any good?

Sawadee

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?? What is the resistance of the heater??

How much current do you expect to put through the heater??

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?? What is the resistance of the heater??

How much current do you expect to put through the heater??



The resistance is about 30-40 Ω. The current is 0.3-0.4 A.


* diagram_heat_controlling_switch_WHAT_mosfet_1.png (14.57 KB, 407x196 - viewed 35 times.)
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did you try to use it, i think it can work .
,
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