HTC200 User Guide

Last updated: 2025-02-11 PDF version
HTC200 Digital heater controller user interface
HTC200 user interface

Supply connector

  • V+: Power supply input (9 V to 33 V).
  • V-: Power supply return.

Communication connector

  • ALM: Alarm output (3V3 logic, see Alarm).
  • INT: Interlock pin (see Interlock).
  • TX: UART TX pin.
  • RX: UART RX pin.

Analog connector

  • AIN: Analog input with a voltage range between 0 and 2.5 V. The voltage at the pin AIN can be retrieved with the ain command.
  • TH+ / TH- Thermistor pins.
  • H+ / H-: Heater connections.

Configuration switch

  • 1: CFG If CFG is ON at start-up, the board will start with the user-defined configuration. Otherwise, the default configuration is loaded.
  • 2: BM This pin is used for firmware update. Set to OFF for normal operation.

Serial interface

The serial interface can be accessed via TX and RX pins on the communication connector (3V3 logic level / 5V tolerant). The serial interface is the only way to configure the HTC200 operating parameters. Once the configuration is done, it can be saved to the internal memory with the save command. If the CFG input is ON at start-up, the HTC200 will load the user-defined configuration and the serial interface is no longer needed.

The HTC200 can be controlled directly from a serial port terminal (e.g. Teraterm on Windows) with the following configuration:

  • Baud rate: 115200
  • Parity: None
  • Bits: 8
  • Stopbits: 1
  • Flow control: None

Example use of the serial port terminal


>>version
V0.1
>>rtset
10000.000000
>>tecon 1
1
>>rtact
10000.023438
>>rtset 12000
12000.000000
>>rtact
11999.853516

Note: Each command must be followed by \r\n.

Control commands

Command Description Type Unit Default Min Max
Settings
tecon Disable | enable TEC/Heater current R/W 0 0 1
rtset Thermistor resistance setpoint R/W Ω 10000.0 rtmin rtmax
tset Temperature setpoint R/W °C 25.0 tmin tmax
Gains
kprop Proportional gain R/W A/°C 0.27 0.0 100.0
tint Integral time R/W s 1.21 0.0 10000.0
tder Differential time R/W s 0.0 0.0 1000.0
sign Feedback sign R/W +1.0 -1.0 +1.0
Limits
tvlim TEC/Heater voltage limit R/W V 20.2 0 20.2
itmin Minimum TEC/Heater current R/W A 0 0 4.1
itmax Maximum TEC/Heater current R/W A 4.1 0 4.1
rtmin Minimum thermistor resistance. If almode set to TPROT, ALM is raised below this value. R/W Ω 1000.0 500.0 200000.0
rtmax Maximum thermistor resistance. If almode set to TPROT, ALM is raised above this value. R/W Ω 15000.0 500.0 1000000.0
rttol Temperature stable thermistor tolerance. If almode set to TSTABLE, ALM is raised when |rtact - rtset| < rttol. R/W Ω 1 0 50000
Monitoring
rtact Actual value of thermistor resistance R Ω
tact Actual value of temperature R °C
itmon Monitored TEC/Heater current R A
itec Set TEC/Heater current R A
vtec Monitored TEC/Heater voltage R V
rtec TEC/Heater resistance R Ω
tboard Board temperature R °C
tjunc TEC/Heater driver junction temperature R °C
vbus Input supply voltage R V
ibus Input supply current R A
ain Analog input voltage R V
Misc
almode Set the ALM mode R/W 0 0 2
intmode Set the INT pin mode R/W 0 0 2
version Firmware version R v0.1
save Save configuration in internal memory (no argument) W
model Return the board model R
serial Return the serial number R
userdata write Write the user data (e.g. userdata write ABC) W 31 chars
userdata Read the user data R
brate UART baud rate R/W baud 115200 9600 460800
err Return the error code in hexadecimal format (no argument) R
errclr Clear the error code (no argument) W

Error codes

The command err returns a 32-bit number in hexadecimal representation which concatenates the detected errors (B0 is the Least Significant Bit):

  • B0: UART_BUFFER_OVERFLOW (err = 1)
  • B1: UART_CMD_BEFORE_PROMPT (err = 2)
  • B2: RESERVED (err = 4)
  • B3: RESERVED (err = 8)
  • B4: BUS_UNDERVOLTAGE (err = 10)
  • B5: BUS_OVERVOLTAGE (err = 20)
  • B6: BUS_OVERCURRENT (err = 40)
  • B7: BUS_OVERPOWER (err = 80)
  • B8: BOARD_OVERTEMPERATURE (err = 100)
  • B9: LOAD_UNDERTEMPERATURE (err = 200)
  • B10: LOAD_OVERTEMPERATURE (err = 400)
  • B11: CMD_UNKNOWN (err = 800)
  • B12: CMD_INVALID_ARG (err = 1000)
  • B13: FET_OVERTEMPERATURE (err = 2000)
  • B14: BOARD_MODEL_UNKNOWN (err = 4000)
  • B15: TVLIM_LOWERED (err = 8000)

Interlock

An optional interlock functionality can be activated with the intmode 1 command. Heater control is enabled when the INT pin is high, else it is disabled. The behavior of the interlock pin can be inverted with the command intmode 2.

Alarm

The ALM output behavior can be set by the almode commmand:

  • 0 (default): ALM is high when an error occured.
  • 1: Temperature stable indicator. ALM is high when actual temperature is within the setpoint for the defined tolerance (that is when |rtact - rtset| < rttol).
  • 2: Temperature protection. ALM is raised when actual temperature tact is outside the defined limits (tmin and tmax). Using this mode the ALM pin can be connected to the interrupt of a current driver to protect the driven device.

Heater voltage limit

The maximum is set by the tvlim commmand.

The default hvlim value is set to 20.2 V and is designed to operate from a nominal 24 V supply.

If the input supply voltage, as given by the vbus commmand, is lower than hvlim + 1 V, then the maximum heater voltage is internally limited to vbus - 1 V and a HVLIM_LOWERED error is raised.

Current source

The HTC200 can also be operated as a standalone current source. You can use for instance the following commands to set the output current to 2 A:


>>tecon 0
0
>>curron 1
1
>>itec 2.0
2.00000

Thermal management

For reliable operation, the baseplate must be properly heatsunk.

If tboard exceeds 85 °C, the controller keeps operating and a BOARD_OVERTEMPERATURE warning is raised. This flag indicates an excessive ambient temperature or improper heatsinking.

If tjunc exceeds 120 °C, the temperature control shuts down and a FET_OVERTEMPERATURE error is raised. For reliable operation, tjunc should not exceed 105 °C for extended periods.

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