I'm hoping to start putting together an electrobus by next weekend to control the fans on my coolermaster. This is the circuit that I will be using: How would I adapt this to run more than one fan, do I need four different REG thingies? Also, I know it isn't entirely wise to control the CPU fan with one of these incase you turn it off by accident, but I would like some control over the noise level on my CPU. Would an Athlon XP 1900+ with an Alpha heatsink burn up if the fan was to be turned off by accident, or could it be ok? Ideally, I'd like there to be four potentiometers. One to control the front two fans, one for top, one for back and one for CPU. Could someone please explain how I would go about achieving this. I don't know much about electronics I'm afraid though. I'm gonna try a diagram of how I think it would be. I'll post it once I'm done.
Don't be afraid, you can test it before you put it in your machine. To run 4 fans simply build four of those circuits, you could use the same molex, it won't mind. THe only danger with having your CPU fan connected to one of these circuits is that you might turn it down too low, stalling the fan. Good luck.
Ooh, I did the diagram again...myself /me is proud is this thing gonna get hot? will i need heatsinks etc.?
With the components shown, the turned-right-down output is about 4v, but you can alter the resisters to get a 7v (or even higher) minimum output, to be safe for cpu fans. Formula is Vout = 1.235(1 + Rtop/Rbottom) so turned down, Vout = 1.235(1+33/14.3) = 4.08v
cpemma, you probably should've clarified what Rtop and Rbottom are, because I thought they were R1 and R2 respectively, and I thought you made a typo with Rbottom. I see that Rbottom is VR1 + R2 now.
I was trying to be clear in my own head which was which cos they're the other way round to a 317 and I'm easily confused. (top is all resistance down to the adjust pin#1, bottom is resistance from adjust pin to ground) I've got one of these LDO regs to try, and was planning on this circuit which gives 6.85v-12.46v in theory. Caps not shown. My reg is the MIC2941ABT, 1.25A but half the price of the 3A MIC29302BT. Pins are different on mine to macroman's 29302 chip shown on his Bit-Tech schematic - 1 Adj 2 Shutdown 3 Ground 4 Input 5 Output (and my Rapid catalogue shows it wrong compared to the datasheet, so be wary )
thanks very much. the minimum cpu voltage will be very useful. I'll probably go for around 7v. I understand how to use the formula too. Thanks. Another question though please, Is it possible to power 5 fans (4 channels, but one channel will control the front two) from a single molex connector? It seems as if it might draw a little too much?
Formula with the MIC29302 is marginally different to the one I put above for the MIC2941, not that it makes much difference compared to component tolerances Vout = 1.24(1 + Rtop/Rbottom) If you want to stick with the macroman layout, R1=100k, VR1=10k, R2=12k gives 6.9v to 12v. But having all the pot above the adjust pin like my layout gives a bit more linear control.
cheers, i think im gonna go for a 5v-12v range and a 7v-12v for cpu. ill do the maths for it later. now down to the practical bit of making this... how am i going to put it all together, stripboard? i dont really like the look of that tbh. Are there any ready made PCBs for this? How much would it cost to get a one-off PCB made? could i make my own?
It's very easy to put together on stripboard, the only awkward bit is bending the ic legs to fit the hole spacing. Get a copy of Stripboard Magic (Useful Lynx) and play. Here's a quick 29152/29302 layout I made earlier - untested, so double-check. And the construction guide: (deleted) The caps are as recommended in the datasheet and only add about 20p to the cost. I'm building one with the 2941 reg so there'll be a tried & tested how-to on my site in a few days. edit: now built with MIC29152, tried & tested, details at http://www.cpemma.co.uk/reg.html#ldo. Above layout & cd have been revised - was too tight for big heatsinks.
