PIC08 Circuit To Control 12v PC Fans

Hi everyone, just looking for some help on an electronics project I'm doing at school. I'm making a PIC08 circuit which controls three 12v computer case fans using a Thermistor as an analogue input. However I discovered that the output voltage I'm getting from the PIC isn't high enough to actually start the fans so I'm having to change my plans slightly.

I'm hoping to change the power supply of the circuit to 12v but use a voltage regulator to bring the voltage going into the PIC down to 4.5 (or 5) volts. However I'm having trouble finding a voltage regulator which has these specifications.

Can anyone recommend what I should do? I will update this post with circuit diagrams later once I have time.

EDIT: Here's the PCB I'm currently using. If possible I don't really want to have to make another.

EDIT 2: Corrected - I am hoping to change the power supply to 12v then bring down the voltage with a regulator.

 

Thanks Harald, so would this be what I'm looking for? http://tinyurl.com/cstnfjv

Part number "TS7805CZ"

 

Thank you for your advice. How would I use a heatsink? Also if it makes a difference, the circuit will be inside of a computer which means it should in theory get some extra cooling.

 

Thanks for your advice. Would this provide better heat dissipation? Or would it just be smaller?



On a side note, can anyone see anything blatantly wrong with my original PCB drawing? I've breadboarded the circuit and it did work with 3v motors (like are seen on the drawing). However I have no way of knowing how the thermistor works, and what values to set my PIC program to.

Thanks.

 

Thanks for all of your help so far everyone...

Please could you look over this PCB designs and see if anything looks wrong? I've added pictures as attachments below.


Also, would this be the right type of heatsink for the voltage regulator previously posted?
http://www.maplin.co.uk/clip-on-to2...arch&utm_campaign=KU50E&utm_content=Heatsinks

I apologise for the large link.

 

Bump.

 

Thank you for your advice.

1) How could I replicate 12v using a battery?

2) I have searched decoupling and this requires a capacitor? What type of capacitor would this be, and where would it be placed in the circuit?

3) How do I put an output cap on a voltage regulator?

Finally, would it be easier to have 2 circuits with 2 different power supplies and connect them with an opto-isolator?

 

1) Using 10 AA cells sounds like a better idea then, thank you.

2) I've added a different track running to the voltage regulator, and I've also added an input capacitor with a diode before it (placed the right way, I hope). I've added an image of my updated PCB design below: is this what you meant?

3) I've taken a quick look at the data sheet and I can't find anything about output caps. Surely the regulator will cap itself? At 10v input, it says that the minumum output is 4.8v and maximum is 5.2v. I'm not sure if this will change as I'm using 12v?
Here's the datasheet: http://html.alldatasheet.com/html-pdf/100156/ETC/TS7805CZ/116/2/TS7805CZ.html

I also have a new problem: on the data sheet it mentions something about linking all of the pins of the voltage regulator to the same negative rail. I've added a diagram below from the data sheet to explain what it means, but do I have to do this?

Thanks.

 

OH. How stupid of me! I thought 'caps' was about capping the output voltage, not capacitor!

Thanks for your help So can anyone see any problems with my circuit?

 

Programming Thermistor As Input For PIC08

This thread follows on from a previous thread regarding a project I'm doing to make an automated PC Fan Controller. The original thead can be found here: https://www.electronicspoint.com/pic08-circuit-control-12v-pc-fans-t254710.html

I am wondering about the values when programming the Thermistor as an input. I would like the fans (all 3 of them) to be activated when the internal PC case temperature is above 35 degrees (for example - I haven't decided on exact temps yet). However, I have no idea what this temperature would be in terms of resistor values or in terms of PIC values.

I will include screenshots of my initial plans for the programme below.


As you can see on the image, it says "b0>10" and "b0>140" it is these values that I am confused about. What do these values (10 and 140 in this example) mean in terms of real world temperature or resistance?


Thanks in advance.