For my GCSE Coursework I'm making an automatic fan controller. The unit will have an output between 0 - 12V according to temperature. There must also be an LED display, something like 10 LED's in a row and when the output is at maximum voltage all 10 will be lit. I had banked on using a PIC but he's not allowing me to The plan now is to find circuits of this nature and use them Does anyone know of circuits that can vary voltage output according to temperature and one similar to the idea I have regarding to the LED's? Thanks in advance, Leeum
You can utilize an Op-Amp and the temperature sensor (Voltage drop I am thinking) to obtain an approximate voltage in relation to the temperature. For the voltage meter, you can either utilize one of those VU meter ICs or build your own from comparators -- you can utilize Op-Amps to do fullswings with a resistor adjustment.
You could modify the 555 PWM circuit that was posted on BiT a while ago (was it cpemma's?) To use a thermister rather than the variable resistor. GCSE examiners love the 555. I dunno how you'd do the LEDs with that though -- perhaps a VU display chip attached to the thermister too? It's all about t3h h4x ch424
A 0V-12V range isn't possible from a linear voltage regulator on a 12V supply. Bottom end is usually about 1.25V, top end about 10.5V with a normal regulator, more with a low-drop-out type. Not that there's any need for such a low minimum, most fans won't start & run reliably below 4V. I'd go for a good low-drop-out regulator such as the MIC29152. That will get very close to the supply (near 11.9V) and works well with common highish-value thermistors. Adding a 10-led bargraph is a standard LM3914 circuit unless you want to complicate things with 10-11 opamps/comparators. Very simple really (for a GCSE project), but you could add a kick-start to get the fan running in cold weather and produce an Excel graph of output voltage v temperature. That single 555 circuit on my site won't do good thermal PWM, the resistance swing on the "potential divider" control needs to be near 0% to near 100% to get the same range of PWM, you wouldn't get that with a thermistor-resistor PD. Could be done with 2 555 chips (or a 556) though, or a few opamps.
