Help with temp. control fan hardware

sorry about the full schematic....the 2nd part is attached
at the moment i only have access to a DC powersupply producing 5,12 and 15 V. triacs are commonly used with ac and thyristors with dc....does that mean thyrisistor is more suitable for me? and how would i go about the ZCD part of the circuit without using an ac power supply ?

can i use a PWM driver instead of this part of the circuit to generate a pulse which will in turn increase or reduce the voltage.

can i use a PWM driver instead of this part of the circuit to generate a pulse which will in turn increase or reduce the voltage.

which driver do you want to use ?

you can use a software generated PWM using 8051 which then requires a devoted timer. the above project can be modified to accommodate PWM, but see if there is a spare timer available (one timer is already used for multiplexing the display).

you can go thru the PWM tutorial on our site for more info.


Arun

@digital-guy, i think you are getting free help but forgetting to thank the moderators, Mr.Arun has clearly explained how the AC fan speed control works and you'll seldom find people who explain the concept in simple terms.

in the code timer1 has been set ( setb tr1) and tr0 has been used for fan speeds. will software generated pwm be in assembly lang and if i can use the pwm then would this mean that my circuit is "complete" . may be if i cannot use the time then would i be able to interface adc with 8051 ?

@digital-guy, i think you are getting free help but forgetting to thank the moderators, Mr.Arun has clearly explained how the AC fan speed control works and you'll seldom find people who explain the concept in simple terms.

Nirmaan

i do thank mr arun kumar for his kind help... but the whole point of this project is to create a DC and not AC fan. i think people should read the whole topic before throwing their questions at other people.

may be if i cannot use the time then would i be able to interface adc with 8051 ?

why do you want to interface ADC to 8051 to control the speed of DC fan ?

i advice you to go thru the PWM tutorial once again and try to see if you can dedicate a spare timer for this job.


Arun

hi arun
since i'm not very good at assembly please correct me where u can...
i understand now the concepts of pwn...basically the voltage depends on how long T.on is. and the maximum voltage e.g. full speed of the fan can be achieved by removing the timer and hence you get Vin.
so does this mean the Vin is the voltage input from the microcontroller (5V)??? or the 12V for the fan????

anyway... for fan off

ORG 0
SJMP START
ORG 03H
SJMP CHECK
ORG 40H
START: MOV P1,#0CFH
SETB IT0
MOV IEN0,#81H
STAY: SJMP STAY
CHECK: JNB P1.0,REVERSE
JNB P1.1,SPEED1
JNB P1.2,SPEED2
SJMP CHECK
SPEED1: ANL CCAPM2,#0FDH
CLR P1.5
ORL CCAPM1,#42H
MOV CCAP1L,#102
MOV CCAP1H,#102
ORL CCON,#40H
RETI
SPEED2: ANL CCAPM2,#0FDH
CLR P1.5
ORL CCAPM1,#42H
MOV CCAP1L,#26
MOV CCAP1H,#26
ORL CCON,#40H
RETI
this is what i know ... i am confused about how the value or the ratio (voltage) i can increment/decrement by pressing buttons :-s
and also this is for manual mode... can u please give me some guidence on how to go about doing the same for auto mode.
and also what about my hardware??? would i stil look like before (attached below)...or now that i am using pwm... it will look different...because i may need to use transistor instead of a tirac
i'm really sorry if im asking too many q's...just need to b clear... thats all:-)

You will need to use a transistor instead of a triac.
A triac will not reliably switch off DC in this case.

The good news is that using such a low voltage you don't need the
opto-isolator.

The transistor can be connected to pin 22 via a resitor.
You probably need to keep R10 as a pull up.

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