tti1908dmm

A small Python toolkit for the Aim-TTi 1908 / 1908P bench multimeter.

It contains:

• tti1908.py, a synchronous Python driver for the meter's SCPI-like USB command set.
• comms_check.py, a tiny communication canary for *IDN?, MODE?, and READ?.
• demo.py, a broader smoke test for the verified measurement modes.
• firmware/flash.py, a native HID firmware flasher based on the vendor bootloader protocol.

This project is independent reverse-engineering work. It is not affiliated with, endorsed by, or supported by Aim-TTi.

Status

The serial driver covers the parts of the command set that have been tested against real hardware:

• identification and status queries
• main-display readings via READ?
• secondary-display readings via READ2?
• DC/AC voltage and current modes
• 2-wire and 4-wire resistance
• diode, continuity, capacitance, frequency, and temperature mode selection
• autorange/manual range switching
• hold, null, min/max, filter, and sampling-speed commands

The firmware flasher can parse TTi-flavoured Intel HEX files and speak the 1908 bootloader HID protocol. Flashing instrument firmware can permanently damage hardware if interrupted or used with the wrong file, so treat it as an expert tool.

Requirements

• Python 3.12 or newer
• pyserial
• hidapi for firmware flashing
• Linux or macOS for the serial driver
• Linux for the bootloader/flasher workflow as currently documented
• Physical access to an Aim-TTi 1908 or 1908P

Install dependencies with:

python3 -m venv venv
venv/bin/pip install -r requirements.txt

On Linux, your user usually needs access to the serial device:

sudo usermod -aG dialout "$USER"
newgrp dialout

For bootloader flashing, you may also need a local udev rule for the HID device.

USB connection notes

Normal operating mode appears as:

103e:04c4

Bootloader mode appears as:

103e:042e

On Linux, the driver first looks for the stable path:

/dev/serial/by-id/usb-TTI_1908_DMM_64638987-if00

It then falls back to /dev/tty.usbmodem* on macOS and /dev/ttyACM* on Linux.

Some 1908 units have a USB descriptor problem when connected directly to strict xHCI/USB 3.x controllers. If Linux logs a message like this, put a physical USB 2.0 hub between the computer and the meter:

config index 0 descriptor too short
cdc_acm ... failed with error -22

When this happens, the kernel fails before this Python code gets a chance to run.

Quick check

With the meter connected and powered on:

venv/bin/python comms_check.py

Expected shape of output:

IDN:   THURLBY THANDAR, 1908, , 1.09
MODE:  VDC, 100mV, AUTO
READ:  0.000000 V DC

Then run the fuller smoke test:

venv/bin/python demo.py

Python usage

from tti1908 import TTI1908

with TTI1908() as dmm:
    print(dmm.idn())

    dmm.vdc()
    reading = dmm.read()
    print(reading)

    dmm.ohms("1000")
    print(dmm.read())

    dmm.autorange()
    dmm.min_max_start()
    # wait while values change
    minimum, maximum = dmm.min_max()
    dmm.cancel_modifier()

read() returns a Reading dataclass:

Reading(value=1.234, unit="V DC", raw="1.234 V DC")

value is None for overload or overflow replies.

Firmware flashing

The firmware flasher is in firmware/flash.py. It replaces the Windows-only vendor flashing utility by speaking the HID bootloader protocol directly through hidapi.

Firmware images are not included in this repository. Download the correct 1908/1908P firmware from Aim-TTi and place the HEX file under firmware/.

Enter bootloader mode:

1. Power off the meter.
2. Hold the rear-panel USB UPDATE button.
3. Power on the meter.
4. Keep holding for about three seconds, then release.
5. Confirm that the bootloader is visible:

lsusb | grep 103e
# expected: 103e:042e

Always dry-run before flashing:

venv/bin/python firmware/flash.py firmware/1908_ALL_109_103.hex --dry-run

Flash only when the dry-run parses the file as expected:

venv/bin/python firmware/flash.py firmware/1908_ALL_109_103.hex

After reboot, verify communication again:

venv/bin/python comms_check.py

Development

Run the unit tests with:

venv/bin/python -m pytest

The tests mock the serial device and exercise the parser, driver wrapper, and firmware HEX parser without requiring a connected meter.

Useful files:

Path	Purpose
tti1908.py	Main driver API and reading parser
comms_check.py	Minimal communication check
demo.py	Hardware smoke test
firmware/flash.py	HID bootloader flasher
tests/	Unit tests that do not require hardware

Known limitations

• The LIMITS command has not behaved reliably on tested firmware.
• Firmware 1.07 could emit binary garbage after some filter/speed sequences; the driver drains stale non-ASCII replies defensively.
• The USB descriptor issue is a device/USB-topology problem, not a bug in this Python code.
• Flashing is inherently risky. Use the dry-run path and keep power and USB cabling stable.

License

MIT. See LICENSE.