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

Mon Nov 25 20:27:35 EST 2013

The MOSFETs that Michael has offered will fit the bill perfectly.

____________________
Peace, Love, Empathy

Alexander Max Rowsell

On 25 November 2013 20:27, Aurelius R <maxrowsell at gmail.com> wrote:

> 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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>>>>> 2. then email Lab at artengine.ca to send your message to the list
>>>>>
>>>>>
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>>>
>>>
>>>
>>
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