[Lab] Help? I can't wrap my head around transistors / mosfets.

[Michael Grant]

I have a few FDB6060L MOSFETs I can spare.
They are logic level, 17 mΩ@ VGS = 4.5 V, and are a bit overkill but
overkill never hurt...

You will also want a 5v regulator for the lilypad if you are running it
from the same battery, and a few caps to stabilize it.
And it wouldn't hurt to put a fast diode across the MOSFET in case the
heater has an unusually large inductive component.

If your at the lab this Wednesday I'll bring a few parts.

Michael Grant
--
http://krazatchu.ca/



On Mon, Nov 25, 2013 at 7:28 PM, Justin Slootsky <justin at slootsky.org>wrote:

> The current requirement at 3.6V is .576A
> The current requirement at 7.2V is 1.152A
>
> We'll likely be using a lilypad Arduino (sewable), but we do have a 3.3V
> and a 5V Trinket available to us if required.
>
>
> ------------------------------
>
> *From: *"Michael Grant" <michael at krazatchu.ca>
> *Cc: *"Justin Slootsky" <justin at slootsky.org>, "lab" <lab at artengine.ca>
> *Sent: *Monday, November 25, 2013 7:24:05 PM
> *Subject: *Re: [Lab] Help? I can't wrap my head around transistors /
> mosfets.
>
>
>
> What's the current required for heater?
> If you don't know, measure the resistance of the heater and apply i = V/R.
>
> This will allow you to choose a capable switching device.
> Likely a logic level MOSFET will be the ideal choice, switched via series
> resistor from the AVR.
>
> And which Arduino are you using?
> Most are 5v but some are 3.3 volts.
>
> Michael Grant
> --
> http://krazatchu.ca/
>
>
> On Mon, Nov 25, 2013 at 6:20 PM, Ken McKinnon <klmckinnon at rogers.com>wrote:
>
>> I started writing a response, but figured someone out there in google
>> land would have a better explanation.
>>
>> Try http://sunburst.usd.edu/~schieber/psyc770/transistors101.html
>>
>> If I recall, the arduino is a 3.3 volt device, so you may need something
>> like a optocoupler in between your arduino and the transistor that would
>> need to be at a bit higher voltage to turn on completely.
>> As an aside, a PWM control would probably control the heat to a much
>> finer degree, with a lot fewer parts....
>> Good luck on your project, if you need more or that link isn't precise
>> enough to get you on path, ping again.
>>
>> Ken
>>
>>
>> On 2013-11-25 4:37 PM, Justin Slootsky wrote:
>>
>>> Hey everyone, I'm having trouble understanding transistors / mosfets,
>>> and what I need.
>>>
>>> I'm working with Chris on a heating project, and we're looking at using
>>> an Arduino to control heating pads in a mitten to keep his hand warm.
>>>
>>> The heater will run on 7.2V, which will generate enough heat to keep
>>> warm but not enough to burn.
>>>
>>> What we would like to do is to regulate the power going to the heating
>>> pad based on the value returned from a temperature sensor.
>>>
>>> I forsee us turning the heater on and off based on threshold
>>> temperatures inside the mitten.  In the future, it might be advantageous
>>> for us to be able to turn the power half on if it is near the desired
>>> temperature but for now a binary on/off based on an output from the Arduino
>>> will do.  (software will determine the on/off cycle based on the value
>>> returned from the temperature sensor).
>>>
>>> My understanding is that we need a mosfet or a transistor or something
>>> for two reasons
>>> 1) The Arduino won't send 7.2V power. (even if we use one that has a
>>> direct battery line, it is too much power to send to the Arduino)
>>> 2) The power draw would be too high anyways.
>>>
>>> Can anyone help me with what I need in order to connect this up?
>>>
>>> Thanks
>>> Justin
>>>
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>>>
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>
>
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