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

[Aurelius R]

I just finished a Skype call with Justin to explain a bit more about
MOSFETs. He already was on the right track so I basically just repeated
what he already knew.

By the way Justin, here's the sample code I wrote. It's for the ATmega644
as I mentioned, but it might help a bit.

____________________
Peace, Love, Empathy

Alexander Max Rowsell


On 25 November 2013 20:11, Michael Grant <michael at krazatchu.ca> wrote:

> 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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