Firmware for the Sinara 8451 Thermostat

• Continuous Integration
• Download latest firmware build

Building

Debian-based systems (tested on Ubuntu 19.10)

• install git, clone this repository
• install rustup

rustup toolchain install nightly
rustup update
rustup target add thumbv7em-none-eabihf --toolchain nightly
rustup default nightly
cargo build --release

The resulting ELF file will be located under target/thumbv7em-none-eabihf/release/thermostat

Network

Connecting

Ethernet, IP: 192.168.1.26/24

Use netcat to connect to port 23/tcp (telnet)

nc -vv 192.168.1.26 23

telnet clients send binary data after connect. Enter \n once to invalidate the first line of input.

Reading ADC input

Set report mode to on for a continuous stream of input data.

The scope of this setting is per TCP session.

Commands

Syntax	Function
report	Show current input
report mode	Show current report mode
report mode <off/on>	Set report mode
pwm	Show current PWM settings
pwm <0/1> max_i_pos <ratio>	Set PWM duty cycle for max_i_pos to ampere
pwm <0/1> max_i_neg <ratio>	Set PWM duty cycle for max_i_neg to ampere
pwm <0/1> max_v <ratio>	Set PWM duty cycle for max_v to volt
pwm <0/1> <volts>	Disengage PID, set i_set DAC to ampere
pwm <0/1> pid	Set PWM to be controlled by PID
center <0/1> <volts>	Set the MAX1968 0A-centerpoint to volts
center <0/1> vref	Set the MAX1968 0A-centerpoint to measure from VREF
pid	Show PID configuration
pid <0/1> target <value>	Set the PID controller target
pid <0/1> kp <value>	Set proportional gain
pid <0/1> ki <value>	Set integral gain
pid <0/1> kd <value>	Set differential gain
pid <0/1> output_min <value>	Set mininum output
pid <0/1> output_max <value>	Set maximum output
pid <0/1> integral_min <value>	Set integral lower bound
pid <0/1> integral_max <value>	Set integral upper bound
s-h	Show Steinhart-Hart equation parameters
s-h <0/1> <t0/b/r0> <value>	Set Steinhart-Hart parameter for a channel
postfilter	Show postfilter settings
postfilter <0/1> off	Disable postfilter
postfilter <0/1> rate <rate>	Set postfilter output data rate
load	Restore configuration from EEPROM
save	Save configuration to EEPROM
reset	Reset the device
ipv4 <X.X.X.X>	Configure IPv4 address

USB

The firmware includes experimental support for acting as a USB-Serial peripheral. Debug logging will be sent there by default (unless build with logging via semihosting.)

Caveat: This logging does not flush its output. Doing so would hang indefinitely if the output is not read by the USB host. Therefore output will be truncated once buffers are full.

Temperature measurement

Connect the thermistor with the SENS pins of the device. Temperature-depending resistance is measured by the AD7172 ADC. To prepare conversion to a temperature, set the Beta parameters for the Steinhart-Hart equation.

Set the base temperature in degrees celsius for the channel 0 thermistor:

s-h 0 t0 20

Set the resistance in Ohms measured at the base temperature t0:

s-h 0 r0 10000

Set the Beta parameter:

s-h 0 b 3800

Thermo-Electric Cooling (TEC)

• Connect Peltier device 0 to TEC0- and TEC0+.
• Connect Peliter device 1 to TEC1- and TEC1+.
• The GND pin is for shielding not for sinking Peltier currents.

Limits

Each of the MAX1968 TEC driver has analog/PWM inputs for setting output limits.

Use the pwm command to see current settings and maximum values.

Limit	Unit	Description
max_v	Volts	Maximum voltage
max_i_pos	Amperes	Maximum positive current
max_i_neg	Amperes	Maximum negative current
	Amperes	Output current control

Example: set the maximum voltage of channel 0 to 1.5 V.

pwm 0 max_v 1.5

Open-loop mode

To manually control TEC output current, omit the limit parameter of the pwm command. Doing so will disengage the PID control for that channel.

Example: set output current of channel 0 to 0 A.

pwm 0 0

PID-stabilized temperature control

Set the target temperature of channel 0 to 20 degrees celsius:

pid 0 target 20

Enter closed-loop mode by switching control of the TEC output current of channel 0 to the PID algorithm:

pwm 0 pid

LED indicators

Name	Color	Meaning
L1	Red	Firmware initializing
L3	Green	Closed-loop mode (PID engaged)
L4	Green	Firmware busy

Reports

Use the bare report command to obtain a single report. Enable continuous reporting with report mode on. Reports are JSON objects with the following keys.

Key	Unit	Description
channel	Integer	Channel 0, or 1
time	Milliseconds	Temperature measurement time
adc	Volts	AD7172 input
sens	Ohms	Thermistor resistance derived from adc
temperature	Degrees Celsius	Steinhart-Hart conversion result derived from sens
pid_engaged	Boolean	true if in closed-loop mode
i_set	Amperes	TEC output current
vref	Volts	MAX1968 VREF (1.5 V)
dac_value	Volts	AD5680 output derived from i_set
dac_feedback	Volts	ADC measurement of the AD5680 output
i_tec	Volts	MAX1968 TEC current monitor
tec_i	Amperes	TEC output current feedback derived from i_tec
tec_u_meas	Volts	Measurement of the voltage across the TEC
pid_output	Amperes	PID control output