Quote:
Originally Posted by DRC It really sounds very simple, but in practice it does take some sizable effort, if not impossible.
To control the AC, with changing load conditions like driving in sun and maintaining say 22 deg, and driving in cold conditions and maitaining the same temperature, and again, imagine a moving car through different ambient temperatures.... it soon becomes very complex an algorithm, and requires something called PID controller (Proportional, Integral, Differential controller). All temp controllers do have this as a module. A very simplistic form of this is implemented only for temperature (not the fan speed) using a bimetal thermal strip in lower end cars (same thing works in controlling the fan in the engine cooling system), This is actually a P controller only with hysterisis is built in by the charecteristics of the the bi-metal strip. but an electronic implementation is quite complex.
My 2 cents |
Sometimes the simplest system is the best, no need of going to mumbo jumbo. I have seen such a switch working, and given few minutes in SJP road market and 2 hours with a circuit board and solder I can make one.
Picture this.
Temparature set to 22 degree.
If temp > 22.5 degrees Swtich on AC
If temp < 21.5 degrees Switch on heater.
How complicated can that be. The switch is easy, very very easy. A simile google search will find you countless circuit diagrams all assemblable by anyone who has spent a semester in any electrical/electroncs lab.
Its the connection part to AC and heater where the modders will come in.
To convince you further, lets take a simple electronic thermometer people keep inside cars
The sensor reads temparature and then displays it on a LCD. It means that it is giving some current to various points on LCD input screen to generate that display, or it can be thermistor which varies resistance based on temparature etc.,
That same sensor can be used for this purpose.
And before you start counting money, the thermometer with dual display and two sensors costs only 300rs.
Go figure.
Now lets come to a complicated microprocessor linked climate control.
All you need is a CPU with some memory to load the program. A CPU with 80386 equivalent computing power is sufficient, and with the board will cost around 2-3000rs.
Thats for you and me. For a company a very nice complicated system cannot cost more than 3-4000rs.
PS: many electronic gadgets you pick up for 20,000rs in the store in India or about 300 US$ cost just 30$ to build(including factoring the cost for designers salaries etc., and leaving out capitol costs of fab etc.,).