Homebrew PCBs

I forgot the most important part !!
Where it is !
http://sites.google.com/site/elettronicaarduinoesperimenti/Home/thermostat-with-ua-741

I used a thermistor, and a BC547 transisor in place of the ua741.
ICs are way too expensive to waste on a thermostat ;-)

ST

On Thu, Dec 24, 2009 at 6:31 PM, saposoft <sapoliste@...> wrote:
> I forgot the most important part !!
> Where it is !
> http://sites.google.com/site/elettronicaarduinoesperimenti/Home/thermostat-with-ua-741
>
>
>

Well Well this is fantastic ... care to share the schematic ? 

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:

>
> I used a thermistor, and a BC547 transisor in place of the ua741.
> ICs are way too expensive to waste on a thermostat ;-)
> 
> ST
> 
> On Thu, Dec 24, 2009 at 6:31 PM, saposoft <sapoliste@...> wrote:
> > I forgot the most important part !!
> > Where it is !
> > http://sites.google.com/site/elettronicaarduinoesperimenti/Home/thermostat-with-ua-741
> >
> >
> >
>

2009/12/24 saposoft <sapoliste@...>:
> Well Well this is fantastic ... care to share the schematic ?
>
> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>>
>> I used a thermistor, and a BC547 transisor in place of the ua741.
>> ICs are way too expensive to waste on a thermostat ;-)

I need to keep a heatsink, its about 3 inches by 2 inches, in a switch
mode psu, cool,  about 35degC would be fine, I have a fan that easily
manages the task, but is noisy if on all the time, so was thinking of
driving the fan via a thermostat circuit so I designed one but havnt
built it yet, and before you say thats a waste of a 741, mine is based
on a 18f2550 !

Why, because I can understand the thing, I can use the a/d converter
to read the thermistor, then get the controller to output PWM to
control the fan speed, I'd never get it working if i went with analog
electronics now!

I'm ashamed to admit i've probably forgotton so much analog that i
know less of it now than when i first got interested in my teens.

I have lost the schematic. I tried to find it when the question came
up a few days ago but can't find it!
There was even a guy in Brazil(?) which duplicated it and made a
webpage, can't find that either.

Anyway you make a voltage divider with a potentiometer and thermistor,
connected between the supply and ground.
The base of the transistor goes in the middle node (output of voltage
divider). Emitter is ground and collector is output (drive relay like
you do).

Depending on wheter you have a PTC or NTC thermistor you need to put
it towards ground or positive supply, the potentiometer vice-versa. If
the potentiometer is towards positive you want to add a series
resistor in case it is adjusted to zero.

When the voltage on the base reaches ~0.7V the transistor turns on.
You can even add hysteresis  by putting a resistor from collector to
base (high value), same as you use R4.

Of course this all depends on supply voltage stability and transistor
junction temperature and... BUT all this seems no problem it works
just fine for years now.

ST

On Thu, Dec 24, 2009 at 6:42 PM, saposoft <sapoliste@...> wrote:
> Well Well this is fantastic ... care to share the schematic ?
>
> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>>
>> I used a thermistor, and a BC547 transisor in place of the ua741.
>> ICs are way too expensive to waste on a thermostat ;-)
>>
>> ST
>>
>> On Thu, Dec 24, 2009 at 6:31 PM, saposoft <sapoliste@...> wrote:
>> > I forgot the most important part !!
>> > Where it is !
>> > http://sites.google.com/site/elettronicaarduinoesperimenti/Home/thermostat-with-ua-741
>> >
>> >
>> >
>>
>
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>

I have a wonderful fan controller circuit!
Here you go:

<http://i46.tinypic.com/2nss26a.gif>

Of course you do not need the voltage regualtor part if you have a
stable DC supply there already. I needed this to operate from a AC
transformer with unstable output.

This circuit is in my two Farnell power supplies (ex military, MASSIVE
fans). They are stopped now most of the time, only when I draw some
power they speed right up. R2 stops the fan speed from oscillating up
and down.

I have also put this circuit in a electronic DC load, it is so sweet
to have it absolutely quiet at no load and speed right up when you put
a few hundred watts into it.

Thinking about it, this circuit may well be the most beautiful I ever
made, just because it is so darn simple and really works perfectly.

_______

As you can see it uses the same idea as the temperature controller for
the laminator, just with a mosfet.


ST

On Thu, Dec 24, 2009 at 6:54 PM, Lez <lez.briddon@googlemail.com> wrote:
> 2009/12/24 saposoft <sapoliste@...>:
>> Well Well this is fantastic ... care to share the schematic ?
>>
>> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>>>
>>> I used a thermistor, and a BC547 transisor in place of the ua741.
>>> ICs are way too expensive to waste on a thermostat ;-)
>
> I need to keep a heatsink, its about 3 inches by 2 inches, in a switch
> mode psu, cool,  about 35degC would be fine, I have a fan that easily
> manages the task, but is noisy if on all the time, so was thinking of
> driving the fan via a thermostat circuit so I designed one but havnt
> built it yet, and before you say thats a waste of a 741, mine is based
> on a 18f2550 !
>
> Why, because I can understand the thing, I can use the a/d converter
> to read the thermistor, then get the controller to output PWM to
> control the fan speed, I'd never get it working if i went with analog
> electronics now!
>
> I'm ashamed to admit i've probably forgotton so much analog that i
> know less of it now than when i first got interested in my teens.
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>