README.md
avrcooling

PC cooling controller for rotary cooling devices (fans/pumps). It has
the following features:


Supports 4 cooling devices.
Can disable devices that still run on minimal PWM.
Monitors devices RPM.
RPM measurement supports pulse stretching.
Supports 2 thermal sensors.
Error signal output.
Can be controlled/queried over RS-232 interface.
Command-line client to query/debug/control the device.
Hardware design and source code is MIT-licensed.


Control algorithm

The control algorithm uses 2 <![CDATA[]]>decision tables<![CDATA[]]>,
one per thermal sensor. Table rows contain the following information:


enabled - whether the control row is enable.
min_temp - lower bound for activating the control row.
max_temp - upper bound for activating the control row.
affect_fan0 - whether to apply the row to fan 0.
affect_fan1 - whether to apply the row to fan 1.
affect_fan2 - whether to apply the row to fan 2.
affect_fan3 - whether to apply the row to fan 3.
fan0_pwm - PWM value to apply for fan 0.
fan1_pwm - PWM value to apply for fan 1.
fan2_pwm - PWM value to apply for fan 2.
fan3_pwm - PWM value to apply for fan 3.


There are 5 rows in each table. The first row with
min_temp...max_temp range including the current temperature is used for
applying the control values.

All cooling fans start initially in disabled state and with
0 PWM. When a fan PWM is set to a value greater than 0 then the fan power is
enabled. When PWM is set to 0 then the fan is also powered down.

Control table rows are checked periodically. The rows can be
read and updated using the command-line PC app described below.

Project structure

The project is divided into 3 subdirectories:


avr - source for microcontroller binary.
hw - physical hardware design.
pc - NodeJS command-line app for communication.


Hardware

Pin allocation




pin  1: reset, connected to VCC and protected by zener diode
pin  2: USART RX line (pullup?)
pin  3: USART TX line
pin  4: PD2, Error signal output
pin  5: PD3, OC2B, fan 4 PWM output
pin  6: PD4, not connected
pin  7: VCC
pin  8: GND
pin  9: XTAL 1
pin 10: XTAL 2
pin 11: PD5, OC0B, fan 2 PWM output
pin 12: PD6, OC0A, fan 1 PWM output
pin 13: PD7, not connected
pin 14: PB0, fan 1 enable
pin 15: PB1, fan 2 enable
pin 16: PB2, fan 3 enable
pin 17: PB3, fan 3 PWM output
pin 18: PB4, fan 4 enable
pin 19: PB5, not connected
pin 20: AVCC, connected to VCC through low-pass filter L1/C13
pin 21: AREF, analog reference, decoupled with 100nF cap C10
pin 22: GND
pin 23: PC0, ADC0, temperature sensor 1 input, low-pass filter R5/C7
pin 24: PC1, ADC1, temperature sensor 2 input, low-pass filter R3/C8
pin 25: PC2, fan 1 RPM input, pull-up, low-pass filter R10/C9
pin 26: PC3, fan 2 RPM input, pull-up, low-pass filter R9/C11
pin 27: PC4, fan 3 RPM input, pull-up, low-pass filter R8/C12
pin 28: PC5, fan 4 RPM input, pull-up, low-pass filter R7/C14


Port directions

Port B


PB0 - output (fan 1 enable)
PB1 - output (fan 2 enable)
PB2 - output (fan 3 enable)
PB3 - output (fan 3 PWM)
PB4 - output (fan 4 enable)
PB5 - output (not connected)
PB6 - output (overriden by xtal)
PB7 - output (overriden by xtal)


Port C


PC0 - input (ADC)
PC1 - input (ADC)
PC2 - input (fan 1 RPM, pull-up)
PC3 - input (fan 2 RPM, pull-up)
PC4 - input (fan 3 RPM, pull-up)
PC5 - input (fan 4 RPM, pull-up)
PC6 - input (default reset config)
PC7 - not in circuit/registry


Port D


PD0 - output (overriden by USART)
PD1 - output (overriden by USART)
PD2 - output (error)
PD3 - output (fan 4 PWM)
PD4 - output (not connected)
PD5 - output (fan 2 PWM)
PD6 - output (fan 1 PWM)
PD7 - output (not connected)


Full schematics

Full schematics in Eagle format can be found in the file hw/schematics.sch.



Part list


C1 10uF/16V
C2 100nF/63V 5mm
C3, C4 22pF/63V 2.54mm
C5 100nF/63V 5mm
C6 10uF/16V 5mm
C7, C8 10nF/100V 5mm
C9, C11, C12, C14 10nF/63V 5mm
C10 100nF/63V 5mm
C13 100nF/63V 5mm
D1 5.1V zener 7.62mm
D2, D3, D4, D5 2N4007
IC1 Atmega88 DIP28
R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11 10k
Q1 12MHz
Q2, Q4, Q6, Q8 2N7000
Q3, Q5, Q7, Q9 IRF9530
L1 10uH
X3 molex power connector, <![CDATA[]]>Farnell product page<![CDATA[]]>
X6, X7, X8, X9 molex 47053-1000 headers, <![CDATA[]]>Farnell product page<![CDATA[]]>


Board layout

Board layout in Eagle format can be found in the file hw/board.brd. Layout
suitable for tone-transfer can be found in the PDF file hw/board.pdf.



Photo of 2 completed units:



Fan connectors

4-wire connectors are standardized in the <![CDATA[]]>specification<![CDATA[]]>.
Connector pinout with typical wire colors is:


1 - GND - black
2 - 12V - yellow
3 - RPM - green
4 - PWM - blue


The max fan current is limited by switch MOSFET channel resistance in ON mode.
This is about 0.3 Ohms. Max dissipation of 1W gives the max current of about 1.9A.



3-wire connectors

3-wire connectors lack PWM signal but are otherwise compatible with
4-wire headers. Pinout:


1 - GND - black
2 - 12V - red
3 - RPM - yellow


While a 3-wire fan lacks PWM control, it can still be made variable-speed by
modulating the supply voltage. This can be implemented with the following
circuit:



Temp. sensor connectors

These connect MCP9700 to the board. There can be up to 2 sensors
connected. The system assumes 0.5V offset and 10mv per °C. This can be
changed by recompiling the firmware.


1 - sensor output
2 - sensor power (5V)
3 - GND


Error signal connector

Error signal is set high whenever an enabled fan's RPM
reads 0. The signal comes directly from MCU and cannot
be directly loaded with higher current than 40mA.


1 - error signal
2 - GND


RS-232 interface

The RS-232 interface is used for updating the control line tables and
for debugging the device. The connector is denoted as X1 on schematics
and board and has the following pinout:


1 - TX line
2 - RX line
3 - GND


A level translator has to be used for connecting the device to PC. PC
uses signal levels -12V/+12V while the device uses normal TTL levels 0V/5V.

A level translator can be built using the <![CDATA[]]>MAX232<![CDATA[]]>
chip or using a prebuilt module/cable/converter. There are various circuits and
building instructions on the Internet.

Compiling firmware

The project contains a Makefile that includes build targets
with <![CDATA[]]>avr-gcc<![CDATA[]]> compiler.

To build the HEX binary for the controller:

cd avr
make


If <![CDATA[]]>avrdude<![CDATA[]]> is installed then the hex file
can be burned into the device with the command:

make burn


Fuses


Clock: Full-swing crystal, BOD enabled
BOD 4.3V


Low fuse


CKDIV8 1 (unprogrammed)
CKOUT 1 (unprogrammed)
SUT1 0 (crystal, BOD enabled)
SUT0 1 (crystal, BOD enabled)
CKSEL3 0
CKSEL2 1
CKSEL1 1
CKSEL0 1


CKSEL is for full-swing crystal osc. lfuse total 11010111 = 0xd7.

High fuse


RSTDISBL 1 (unprogrammed)
DWEN 1 (unprogrammed)
SPIEN 0 (programmed)
WDTON 1 (unprogrammed)
EESAVE 1 (unprogrammed)
BODLEVEL2 1
BODLEVEL1 0
BODLEVEL0 0


hfuse total 11011100 = 0xdc.

If avrdude is installed then correct fuses can be burned
using the command:

make burn-fuse


Client

The client application is used for updating the control table lines
and for debugging the device.

Client options and supported commands:

Usage: avrcooling --port <port> --command <command> [arguments]
Recognized commands:
  disable0       disable fan 0
  disable1       disable fan 1
  disable2       disable fan 2
  disable3       disable fan 3
  echo           sends and receives the given byte
  enable0        enable fan 0
  enable1        enable fan 1
  enable2        enable fan 2
  enable3        enable fan 3
  nostretch0     disable pulse stretch for fan 0
  nostretch1     disable pulse stretch for fan 1
  nostretch2     disable pulse stretch for fan 2
  nostretch3     disable pulse stretch for fan 3
  pwm0get       query fan 0 PWM level (0-255)
  pwm0set       set fan 0 PWM (0-255)
  pwm1get       query fan 1 PWM level (0-255)
  pwm1set       set fan 1 PWM (0-255)
  pwm2get       query fan 2 PWM level (0-255)
  pwm2set       set fan 2 PWM (0-255)
  pwm3get       query fan 3 PWM level (0-255)
  pwm3set       set fan 3 PWM (0-255)
  rpm0           query fan 0 RPM
  rpm1           query fan 1 RPM
  rpm2           query fan 2 RPM
  rpm3           query fan 3 RPM
  stretch0       enable pulse stretch for fan 0
  stretch1       enable pulse stretch for fan 1
  stretch2       enable pulse stretch for fan 2
  stretch3       enable pulse stretch for fan 3
  stretchinfo   query pulse stretch settings
  temp0          query sensor 0 temperature
  temp0lineget get control table line (0-4) for sensor 0
  temp0lineset set control table line (0-4) for sensor 0
  temp1          query sensor 1 temperature
  temp1lineget get control table line (0-4) for sensor 1
  temp1line_set set control table line (0-4) for sensor 1




Debugging

Set environment variable DEBUG=* and run the command.

DEBUG=* avrcooling ...


Installation

Assuming that you have <![CDATA[]]>NodeJS<![CDATA[]]> installed:

npm install -g avrcooling


Protocol

The client-device communication protocol terminates messages with line ends.
Data on individual lines is encoded in the hex encoding.

Decoded commands have the following format:

[commandbyte, arguments..., checksumbyte]


Responses have the following format:

[responseok, response arguments..., checksumbyte]


or

[responsefail, checksumbyte]


or

[commandchecksumfail, checksum_byte]


Multibyte integers are sent in big-endian format. Maximum decoded message length is 10 bytes.
The detailed description of the protocol is found in pc/lib/commands.js.

The checksum computation uses the Pearson hash algorithm:
<![CDATA[]]>http://en.wikipedia.org/wiki/Pearson_hashing<![CDATA[]]>. The constants
table can be found in avr/src/pearson.c.

Changelog


2016-01-31 BOD (brown-out detection) enabled.
2015-03-24 Pulse stretching is implemented. Client code is finished.
2014-07-27 Client code is mostly working.
2014-07-17 AVR code is mostly working.
2014-02-01 Physical hardware design is ready.


Known issues


Max ADC input voltage is 1.1V when the internal reference is selected (by default).
Temperature sensor MCP9700 needs 100nF decoupling cap at the sensor to ensure
stable operation.


License

The MIT License. See the LICENSE file.