Re: 555 timer circuit controlled by tempreture?...help please

tel1e@xxxxxxxxxxx wrote:
On 25 Jan, 14:55, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@xxxxxxxxxxx> wrote:

On 25 Jan, 01:50, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@xxxxxxxxxxx> wrote:

down load LTSpice.
copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -


Hi
Ok Jamie I have done that (Thanks) & I can now see a circuit diagram.

I'm not sure what this is...is it a bespoke circuit for my needs?

Will this supply power to the heater until it reaches a determined
temperature (15 degrees C) ?

Sorry for all the questions but I'm lost with this stuff & really
don't understand.

Thanks.

U2 is a PTC "Positive Temperature Coefficient" resistor.
you'll want that close to the heater resistors which is
assumed to be on the Uc chip?

The PTC will increase in value as the temperature raises.
You need to shop around for the PTC from mouser, Digikey etc..
they come in various values and spec'd differently. for example
many are rated at what's considered room temperature, (25C)/77F.

R1 can be recalculated to match the PTC you get so that the voltage
at the network (- input) is just above the voltage at the (+) input
of the comparator at 15C. For example, 6.2 volts at (-) input at 15C would
be ok. you must think of this in terms of a voltage divider.

C1 and R4 is part of the timer, the two select the time and depth
of the threshold on the time cycle. You could actually omit these two
components from the circuit if all you want is a temperature switch.

If it's very cold, the PTC will most likely prevent the timer from
turning off the heaters until the PTC registers heat from the heater
resisters. If the temp is near the 15C, then the heaters will come on
and then off during the 5 sec window. As the initial temperature is
higher the timer will expire sooner, until at which point, the initial
temperature will be high enough to where the (-) input of the comparator
will be lower than the initial starting voltage at the (+) input, which
is calculated via the C1 and R4 and thus never turned on.

Q1, is a PNP power transistor. it must be large enough to handle
a 2 Amp load which shouldn't be a problem to locate..

The comparator used here, need not be the LTxxxx type here, you can
use others in place of it.
LM393 for example.
http://i2c2p.twibright.com/data***/LM193.pdf

You could even use an old LM741 to drive it. It really does not matter in this circuit...

http://webpages.charter.net/jamie_5";

.

Quantcast