Need help making Temp sensor w/LCD and also

[Crappyone]

Hello there I am an electronics engineer student. I have only been taught the basics I'd say so far. I can understand stuff pretty well, but I just have a hard time getting started off. I'll let you guy know what I want to do and you guys know if you can help me.
Well I'm looking to make a panel on my Case to have 3 - Rheostats (1 for Front 2 fans, 1 for Rear 2, and 1 for 2 on Radiator). I would also like to have about 4-5 LEDs next to each Rheostat and have them light up as the Voltage increases/Fan speed. Next to them I would like to have an LCD screen that I can have tell temps of Inline water sensors and any other sensors I add later. I read through MANY MANY tutorials about this stuff but I guess I'm still to new to Electronics and can't figure out how to Atleast start drawing a schematic diagram.
Any help would be appreciated. Thank you

 

[Frank4d]

I can think of a few ways to control fan speed (assuming you are using 12 volts as the source, and want the speed to be variable):
- Potentiometer in series with the fan. This is cheap and easy, but also requires you to choose a potentiometer resistance value and wattage rating that is suitable for the fan. This will vary depending on the fan.
- Rheostat across the 12 volt supply with the wiper connected to the fan. This is also cheap and easy, but typically the resistance must be low compared to the fan so it burns more power. Same as above... you need to choose a potentiometer resistance value and wattage rating that is suitable for the fan. This will vary depending on the fan.
- Adjustable regulator (LM317 type or equivalent). Typical circuit needs one resistor and a potentiometer. Output voltage is not affected by what fan you use (as long as you use a LM317 with high enough current rating), but you will not get a full 12 volts out for 12 volts in... more like 10.8 volts max.

For the LEDs, a LM3914 chip will light up LEDs proportional to the input voltage.

You could also control the fans using pulse width modulation (PWM) which applies a 12 volt square wave to the fan, controlling speed by varying the duty cycle ot the AC applied. But interfacing this to LEDs that light as the fan speed increases would be more challenging.

 

[Whatsisname]

Having an LCD display stuff would require usage of a microcontroller unless you were to interface it with the computer then run temperature monitoring software along with the lcd driver software. With the microcontroller you would be able to have multiple temp sensors with ease as opposed to the PC, and you could use PWM to control the fans, much better for the fan and it saves power, as well as allowing you to use cheapo bargain bin potentiometers. Furthermore it would allow the whole fan controller assembly to be an isolated unit that could be moved from computer or computer.

Although it sounds complicated, it shouldn't be too difficult depending on how much time and money you are willing to invest.

 

[Fenris_Ulf]

If you just want the LCD to display temps, this is pretty easy. About 5 years ago I built a display like this for my watercooled rig. The least expensive way is to get a rotary switch, simple voltage based LCD display (for example) and some thermisistors. The rotary switch determines which thermisistor is being read by the display. I used the -12 and +12v lines from the power supply to give me a 24 volt differential which I then used with the thermisistor and another resistor and op-amp to give me a voltage that was approximately equal to one tenth the temperature in degrees F. The LCD displays the voltage and the decimal place is moved by one of the jumpers on the LCD, resulting in the display of degrees. It sounds complicated, but it's not that difficult once you understand and you would learn a great deal about analog electronics, especially voltage dividers and single supply op-amps.