UNI-T UT325

UNI-T UT325

The UNI-T UT325 is a logging thermometer with two thermocouple inputs and USB connectivity. It supports K,J,T,E,R,S,N thermocouple types.

See UNI-T UT325/Info for more details about the device.

Hardware

• Texas Instruments msp430fe427 (MSP430) microcontroller with 32KiB flash.
• ATMEL 16KiB EEPROM, various models.
• WCH CH9325 USB interface chip.
• Holtek HT1621B LCD driver.

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Protocol

The device communicates with the host via a WCH CH9325 USB interface chip. See the protocol section of that page to extract the protocol as described here.

Commands

Byte	Description
0x01	Start sending realtime data
0x02	Stop sending data
0x07	Start sending stored data

Received data

Temperature is encoded as ASCII digits. The number represents the temperature * 10. Unused digits are represented by 0x34 (ASCII colon), and should be ignored. A completely invalid measurement is represented as four times 0x3b (ASCII semicolon). This happens when no probe is connected.

The data comes out of the USB HID encoding in packets of 19 bytes each:

Byte	Description
0	unknown
1-4	Current probe temperature.
5	ASCII digit 1-3, representing the measurement unit: Celcius, Fahrenheit or Kelvin respectively, or 0 when unknown (in recall mode; unit is not stored.)
6-7	Number of stored reading in recall mode, as ASCII digits 00-99. Always 00 in realtime mode.
8	Unused, always 0x30.
9-10	Hour, as ASCII digits.
11-12	Minutes, as ASCII digits.
13	Selected probe, as ASCII digits 0-3: 0=T1, 1=T2, 2=T1-T2 (T1 on main display, 3=T1-T2 (T2 on main display).
14
15
16
17-18	Always 0x0d 0x0a (CRLF), denoting end of packet.

Resources

• Jumper One: UNI-T UT325 Thermometer Review
• Jumper One: Uni-T UT325 Thermometer tear down