Help with temp. control fan hardware

yes that one will be fine, you need to connect a Diode across motor to prevent back emf.

so do i just need a normal (2n2222) transistor? i will need to drive a 12V dc motor

yes that one will be fine, you need to connect a Diode across motor to prevent back emf.

without knowing the rating of your DC 12 V motor if you connect it to the poor 2n2222 transi you could see smoke coming up !

first find out what is the motor's current consumption using multimeter, i,e how much milliamps/amps the motor draws when connected to +12 Volts

micro like 8051 can only provide(source) 1 mA current @ 5 volts and that small current is not sufficient to turn ON a transistor fully, so better use a darlington transistor ( which has 2 transi inside, one with high gain and the other with high power) or even better a mosfet N channel .

all this can be ascertained only if we know the current consumption of the DC motor.



Arun

hi
so the only thing different on my hardware is that i replace the tirac with the darlington transistor...and i would stil need opto-isolator as i want to separate 5v from uC and 12v for fan...rite ??
how would i connect the transistor to my 12V and the opto isolator ?? and also can u please check my code that i posted earlier ...

first find out what is the motor's current consumption using multimeter, i,e how much milliamps/amps the motor draws when connected to +12 Volts

all this can be ascertained only if we know the current consumption of the DC motor.

you haven't given the current consumption, yet

and i would stil need opto-isolator as i want to separate 5v from uC and 12v for fan...rite ??

opto-coupler is not required, but you can use it only to protect the micro from EMI from motor. even without opto, it will work.




Arun

i was planning to use a multimeter instead of motor for now to see the variation in voltages and if it all goes accordin to plan...but i want to use a 12Vdc , 14.4W, 1200mA fan...if possible with current configurations. so since there might not be any need for opto-isolator and tirac... would the pin22 from uC go straight into the darlington transistor???

not straight,but through a 1k current limiting resistor into the base.
You may use an npn darlington like TIP121 for the job....

Now after seeing your Dc Fan's current rating, you can surely not use puny transistors like 2n2222 or BC337 etc since your fan consumes quiet amount of current, you have to use a N- channel Power mosfet like IRFZ44N or IRF540N they are easily available bcoz they are extensively used in UPS and Inverters.

and yes you can directly connect the Port pin22 ( with a pull up already installed) to the gate of the mosfet without any series resistor between the port pin and the gate of the mosfet bcoz mosfets are voltage driven devices unlike transistors which are current driven.



Arun



Arun

can i use any power mosfet as long as it has the same specs of irf540n e.g. VDss 100V, RDS(on) 40m ohm, ID 33A. ? and pin22 will go into the Gate? and 12V go into the source and the fan's +ve wire go into the drain and the fan's -ve wire into the ground ??

Be careful, you have to use N-channel power mosfet

and pin22 will go into the Gate? and 12V go into the source and the fan's +ve wire go into the drain and the fan's -ve wire into the ground ??

your connection is wrong, its connected like this; pin22 (with a 10K pull up already connected) to the gate (without any series resistor), +12 Volts to Fan's positive and fan's negative wire connected to the Drain of Mosfet, source is connected to Ground.

you should have a diode across the motor to protect the mosfet from EMF back kicks. just like you have diode across a relay. here's diagram to clear things (diode is missing though)





Arun

so will the diode be placed as it is on the diagram below? and which type of diode i need... i noticed you have 2 connections going to the gate... shall i just ignore one and do the one with p22 without the 10k. and can i use any mosfet as long as it has the same specs as IRFZ46N ???

i also forgot to mention that i am using an 8pin ds1820 instead of a 3 pin one... would it matter if i connect it up in the same..??