HVAC Control on Car PC through Serial Port.

**Mastero** · 05-28-2005, 05:16 AM

Originally Posted by Chris31

RC servo operates on PWM. If the knobs have 3 position, all thats needed is to find out whats the PWM values are to get to those 3 position.

For simplicity sake,

A 555 timer is used to generate the PWM. (Circuit can be found easily by googling)

3 variable resistor each defining the position of the servo can be used. One of the variable resistor is switched into the 555 timer by means of the bits from a parallel port.

Again, to make thing simple small reed relay are used to switch the variable resistors into the PWM circuit...moving the servo to the required position.

Its a ghetto way for non so techie poeple. Should work as well.

Ill never do it this way though

Chris ... i can free two LPT bits ... so say we can have two servo control. the bits can be timed pluse or always on ...

If the 555 timer can be designed so the each pluse on the trigger will change the servo position that shall be nice.

Meaning if you hit the trigger with one pluse the servo will move to x position and stay there, then when you hit the pluse again the servo will move to y position and stay there.. so on ..

You think you can put the design on paper? for the 555 timer

Let me know.

Then we can use two of this to control the vents and the air circulation

mastero

**Chris31** · 05-28-2005, 11:33 AM

Originally Posted by Mastero

If the 555 timer can be designed so the each pluse on the trigger will change the servo position that shall be nice.

Of course it can be done that way but how is the PC able to track where the servo is currently at?

Use 2 bits from the parallel port to provide the position.

00 = OFF position
01 = 1
10 = 2
11 = 3

This way the PC always know where the servo is.

**Mastero** · 05-28-2005, 03:37 PM

Originally Posted by Chris31

Of course it can be done that way but how is the PC able to track where the servo is currently at?

That can be done ....... waiting for the hardware design chris..?

Mastero

**Chris31** · 05-28-2005, 05:11 PM

Originally Posted by Mastero

That can be done ....... waiting for the hardware design chris..?

Mastero

Waiting for whos design?

**Mastero** · 05-28-2005, 06:59 PM

Originally Posted by Chris31

Waiting for whos design?

I taught you had the design .. in mind ......do you ...?

Mastero

**Chris31** · 05-28-2005, 07:33 PM

No, it just a thought that I reckon that can be done quite easily.

Search for 555 timer servo PWM control or something.

Then just use a small relay to switch the potentiometer in the circuit...or better to use an electronic switch. Then just control the switch by the parallel port.

Pretty much job done really.

**Chris31** · 05-28-2005, 08:26 PM

http://home.earthlink.net/~tdickens/...rvo/servo.html

**Mastero** · 05-28-2005, 09:27 PM

chris i know the 555 and the 556 generates PWM

but my concern is how does one change the servo position from x to y to z using the same trigger .. and not changing any hardware

mastero

**Chris31** · 05-28-2005, 09:50 PM

Ok use 74HC4016 or 74HC4066. It contains 4 electronics switches, controlled by individual lines.

You need to control 1 of the 4 lines by another chip.

The 74HC4017 is a clocked decimal counter. Use the reset line when the output reach 5.

**Mastero** · 05-29-2005, 05:35 AM

Originally Posted by Chris31

Ok use 74HC4016 or 74HC4066. It contains 4 electronics switches, controlled by individual lines.

You need to control 1 of the 4 lines by another chip.

The 74HC4017 is a clocked decimal counter. Use the reset line when the output reach 5.

Ok chris lets not just add posts to this thread.....

Can you put your idea on paper ...

Mastero