temp lcd

I found an old case that hadn't been used in years; it has the old "speed" lcd (?) that used to tell the cpu speed; would it be possible to rig this up and incorporate it into my case to monitor the cpu temp? I'm a complete noob regarding anything electrical so not sure if/how to go about it even if its possible; btw, it is a 3 digit thing!

Its possible. You'll need to determine if it has a serial interface, wire it up to an external serial port, and find a correct software interface to communicate with it.

It'd be possible, albiet a royal pain. Every one of those displays (they're almost always LED arrays, like on alarm clocks) were quite simplistic devices. Generally the display was wired up so that if the turbo signal from the mobo was low, it'd pass electricity into one bank of connectors (which would corrispond to the non-turbo readout on the screen), and in the presence of the turbo signal, switched the current over to another bank of display LEDs.

If you're lucky, just behind the display there'll be a bunch of jumpers that corrispond to the LED units that light up under either condition (I had a kick turning my 486 DX2 66MHz into 99MHz back in the day . Making these light up in a series of numbers is possible with thermistor input, but that'd be quite difficult. If each digit is either a 7 or 8 unit LED display, you can use a 7490 and a 7448 IC (the 7490 will take pulses of electricity, count them, and send the data to the 7448, which will convert them to a 0-9 number on the LED display).

A simplier idea (which the above could be piggybacked on to) would be to use a calibrated thermistor bar graph readout: since transistors generally act as a switch when around 0.6VDC hits their base connector, by taking the +6VDC line from the power supply, passing it through a thermistor, and having a bank of something like 10 or 12 transistors which have varying resistance applied to their base connector to only allow them to trigger if X power came in, you could make designs on the display pretty easily corrisponding to fixed temperatures.

Example: +6VDC in to the thermistor, the thermistor (at let's say 30 deg c) cuts that down to 2VDC, and you have essentially an if-then-else bank of transistor+resistor combos - IE transistor 1 and 2 trigger at 2VDC, but transistor 3 doesn't trigger until 2.6VDC, thus LEDs hooked to tranny 1+2 light up.

I can post more detailed stuff about the latter setup if you'd like, otherwise good luck ^_^

yo lucky bob since u said u can post more details on how to make this simply circuit can u do that i wana try it

I would like some more info too; just hope I can understand it!!!lol

/me assumes no responsibility for this circuit, and he lets everybody know that it's been a while since he's done something like this



Notes:
R1 - As *very* few LEDs can handle the straight +6VDC out of the power supply, this resistor is necessary to cut the power down to an acceptable level. As for value, it's a question of what the LEDs in the display can handle. If you're recycling an old display from a 486 or something it's anybody's guess. I'd try gearing it for about 1.5VDC @ 30mA to start (formula for this to follow later); test one element on the display and see how bright it is. If it's too much power, it'll blow the element or the color will change from green to yellowish and blow later. If it's too little power, it'll be really dim. You'll have to experiment. The other option is to go to Radio Shack (since the stuff here requires a trip anyway ^_^) and buy a 7 or 8 segment display, or better yet one of their 10 segment red bar graphs.

Formula for R1:
R1 = (6VDC - LEDv)/LEDi
LEDv = voltage the LED requires. If you want it to last a long time, short change it a bit.
LEDi = current the LED requires. Same as above.

Ra-Rg:
These are the control resistors. The termistor you can buy from Radio Shack increases in resistance as the tempature drops, and each of the NPN transistors has an approximate trigger voltage of 0.6VDC. By (for example) steadily increasing the resistance from Ra to Rg, LEDs A through G will light in order as the temperature increases. You'll have to manually test these individually to find the values you want, since the Radio Shack thermistor doesn't spec any particular resistance at any particular temperature. I think the easiest way to do this would be (when breadboarding the design) to use something like a 10kOhm potentiometer, heat the thermistor to a particular temp, then adjust the pot until the LED lights. Then get an ohmmeter and read the value of the pot.

Brightness control:
Most likely a 1kOhm potentiometer. This should give suffecient control.

This whole thing assumes at least some experience building electronic circuits, and sadly since two of the components aren't known (the power the LED requires and the temperature curve of the thermistor), I can't post exact values for everything. It'll have to be experiemented with. All in all I think you could build this setup for less than $25 provided you've already got an ohmmeter and a soldering iron.

Thanks LuckyBob; from everything you said, I do understand one thing---I do have a soldering iron---just have never used it! But I do appreciate the help; what I'm going to do is print out your diagram, take it to my local ratshack and see if they can tell me what I need and what to do! thanks again;