Voltage regulation with Arduino

[SaleB]

Hello,

I have yet again come with another problem and willingness to learn.

There is a custom made computer case that will function headless (without the motherboard), it's rather a box for 12x hard drives (at a later date extendable to 24), psu, 8x fans and one backplate. In a development stage I have come to the problem of active fan speed control. Computer fan typically uses <200mA@12V.

I intended to use Arduino with a few temperature sensors and a control circuit for fan speed another circuit to collect fan speed data. The research on the topic of fan speed control proved to be rather difficult. First idea was to use pwm, but I could not find any simple and reliable solution. Using a serially controlled LDO regulator for each fan seem as an overkill. So, the simplest solution would be to control a series of FETs with analogWrite, but then I do not have enough analog pins on arduino mini pro. There won't be a problem to use more then one arduino, but if there is an elegant and reliable solution that I have not thought about, I would like to know about it.

Thankful in advance

[stj]

Re: Voltage regulation with Arduino

you cant part-drive a fet.

use a microcontroller with hardware pwm or write your own code using hardware timers.
use the pwm output to drive a fet.

[SaleB]

Re: Voltage regulation with Arduino

Thank you for your answer. I have accidentally found an alternative solution, an IC that would allow me to use PWM control rather then FET's. On the first look it seems like much simpler/better solution. The name of the IC is PCA9685. It uses I2C to communicate with the microcontroller.

For the other problem of collecting sensor data I have found that 4051/4067 circuits may be usable. A quick question here, is there an alternative to 4051/4067 that would use serial selector input or also I2C for selection rather then 3-4 digital lines?

It seems much simpler to organize the board if one mux collects temperature data, another speeds and a before mentioned PWM circuit controls the fans.

[stj]

Re: Voltage regulation with Arduino

you still need fets, that pca chi is 25ma drive - a fan needs upto 300ma

i dont know why your wasting time muxing sensors, AVR's have 6 or more ADC's on them.

[mariushm]

Re: Voltage regulation with Arduino

Sigh... microchip microcontrollers are powerful enough to send a pwm signal on that 4th wire of regular fans to adjust the speed.

But you can be smarter and use ready-made fan controller chips, for example see this 2$ EMC2305 chip Microchip makes which can control up to 5 4-pin fans and since it works on SMBus you can link up to 6 of these in a chain to control up to 30 fans : http://www.microchip.com/wwwproducts/en/EMC2305

(US) Digikey link: http://www.digikey.com/product-detai...-CT-ND/4490169

(EU) Farnell : http://uk.farnell.com/microchip/emc2...pwm/dp/2361972

If you can't order from you country, I'm sure someone could here could order a few for you and mail them to you.

SMBus is similar to i2c and you can find ready made code to talk to SMBus devices using arduino, so you can just talk to them using Arduino's i2c and connect your arduino to your computer using a rs232/uart to usb adapter.
Then you just open putty on usb serial port and send commands to your arduino through the rs232 to usb adapter or receive the temperature readings and the rotation speeds of all fans (which you can read from the fan controller chips through smbus)
You'll find tutorials about arduino and serial online, you'll find tutorials about arduino and temperature sensor chips (See below) like this one for example (didn't watch it skipped through it and sounds good to me) : https://www.youtube.com/watch?v=_fNto4JOu4E

Arduino also has some adcs so you can also get a bunch of cheap temperature sensor chips that take some voltage (ideally stick with 3.6v or less since the above chip works at 3.6v or less and arduino chips also work at such low voltages) and you can use arduino's internal ADC to take temperature measurements every few seconds and adjust the fans accordingly.
Here's some example of very basic temperature chips, they have +/- 2c accuracy or better. You shouldn't need more than this accuracy :


MCP9700 (10mV per C, 500mV at 0C) : http://uk.farnell.com/microchip/mcp9...c70/dp/1332165
MCP9700 (10mV per C, 500mV at 0C, through hole) : http://uk.farnell.com/microchip/mcp9...-92/dp/1332166
MCP9701 (19.5mV per C , 400mV at 0C, through hole ) : http://uk.farnell.com/microchip/mcp9...-to/dp/1439483

LMT89DCKT (+/- 1.5c accuracy , VO = −11.69 mV/°C x T + 1.8663 V ) : http://uk.farnell.com/texas-instrume...deg/dp/2314391
LMT85DCKT (+/- 0.4C accuracy, V = (-8.20 mV / °C) x T + 1569 mV) : http://uk.farnell.com/texas-instrume...deg/dp/2314387

etc more to pick from here: http://uk.farnell.com/ic-sensors_temperature-sensors





Basically glue these to something using double sided thermal paste or some silicone and thermal grease and you have cheap and simple temperature reading