Uni-T UT210E Clamp Meter

Uni-T UT210E Clamp Meter

This doc is the result of explorations into modding the Uni-T UT210E Clamp Meter; it's what I'd wish I'd had before wading through pages and pages of forum posts and datasheets across at least three languages. If you just want to know how to modify a UT210E using a Bus Pirate, skip to the end.

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• Uni-T UT210E Clamp Meter
  • Overview
  • Hacking
    • Configuration Data
    • Interesting Addresses
    • Timeouts
    • Modes
      • Meter Labelling / OEM Spec vs Chipset Modes
      • Changing Meter Function
    • Ranging
    • Changing Counts
      • AC RMS Headroom
      • Zeroing & Auto-Range Limitation
      • Zeroing 2000 Counts Bug
  • Reading/Writing the EEPROM Using a Bus Pirate
    • Configuration
      • Modify the auto-off and backlight times
      • Other Mods

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Overview

Specifications (OEM/as-manufactured)

• 2000 count resolution
• 0.7% DC accuracy
• AC bandwidth 1kHz (DTM0660L ASIC datasheet), measured to ~3 kHz (ref), True RMS ("virtual", using DSP)
• DC current measurement, 2A-100A ranges, ~2% accuracy
• Non-Contact Voltmeter (NCV)
• 600V Cat II (safe for mains appliances, etc)
• continuity, resistance, diode check and wide ranging capacitance

Pros

• good specs for the price
• diode test 3.25V (so can test blue and white LEDs)
• DMM IC has been community documented incl. EEPROM configuration, i.e. "hackable"

Cons

• clamp meter is very sensitive to metal and magnetic fields and cable orientation
• can't handle AC with a DC offset (ref)
• Voltage and Ω/F are auto-range only; current is manual ranging only
• RMS is calculated via DSP rather than directly measured, this has ramifications if modifying the meter's ranges
• not the fastest display update rate nor auto-ranging response

Misc functions/features

• all ranges start on AC, have to press Select button to change to DC (can be modded)
• auto power off (APO) (15 mins, can be modded)
  • LCD indicator when APO is enabled:
  • hold down SELECT button during power on to disable
• beeper sounds on over-range (can be modded)
• "VFC": apparently reduces bandwidth to 400Hz - intended for measurements on switched variable frequency systems (e.g. motors)

Reviews

• https://lygte-info.dk/review/DMMUNI-TUT210E%20UK.html
• https://www.markhennessy.co.uk/budget_multimeters/unit_ut210e.htm

Hacking

Refs:

• https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/
• http://www.kerrywong.com/2016/03/19/hacking-dtm0660l-based-multimeters/

The meter is built around a Digital Multimeter (DMM) ASIC, two variants have been used at various times:

1. DTM0660L (older units)

• partially translated DTM0660 data sheet
• maximum count: 4000/6000 (9999 for frequency and capacitance)

2. DM1106EN (newer units)

• maximum count 9999

The above ASICs are allegedly clones or rebranded versions of the HyconTek HY12P66. At least some variants have no markings on the IC; presumably DM1106EN.

The board is labelled "UT210E Rev.1", appears to have not changed across variants.

The ASIC's configuration is stored on EEPROM and can be modified to:

• change the backlight and auto power off times
• default to DC than AC for voltage and current modes
• change number of counts: from 2000 to 6000
• ? enable support for sigrok via serial/UART (requires additional hardware modification)

Device-specific calibration data is also stored in the EEPROM so need to be careful and only selectively modify its contents.

There are a couple of editors available that provide a user-friendly way of viewing and changing the EEPROM configuration, including:

• adlerweb: https://adlerweb.github.io/UT210E-Calculator/
• devydd: https://devydd.github.io/UT210E-EEPROM-Editor/

The EEPROM is an I2C SOIC8 2kbit (256 byte) device - the specific part can vary; presumably Uni-T use whatever is cheapest at the time of manufacture. The DM24C02A is common, though a T24C02A 1kB device has been seen in the wild (with the content above 0x100 empty).

The EEPROM's pins are available on an unpopulated 2mm-pitch jumper/connector CZ1. A SOIC clip works fine - though may need the neighbouring caps nudged aside.

The CZ1 connections are directly to the EEPROM's power and data pins, and presuming CZ1's "pin 1" is the pin closest to the crystal (i.e. the photo above is upside-down), we have:

1: Vcc (+3.3V)
2: WP
3: SCL
4: SDA
5: Vss (0V)

(aside: the DM24C02A is CMOS, so Vcc should be labelled as V_DD)

Note that the testpoint marked GND on the board near C2 is analogue input ground, not Vss / battery negative.

Reading/writing the EEPROM:

• the ASIC should be held in reset: pin 55 to GND
  • pin 55 is connected to GND via C5 (and to V_DD/+3 V via R1, making an RC reset circuit)
    • i.e. temporarily short C5, or (potentially easier) hold a grounded probe on C5's leg closest to the ASIC when reading/writing
  • seems that if you leave the power on for a while you can get away with not holding the chip in reset, however if you're getting inconsistent results from read to read then you may be best to hold it reset
    • obviously you need to be confident you've made a good "backup" before doing any writes, and it's always a good idea to verify all writes by reading back
• the EEPROM's address bits are all tied low with a base address of 0x50, so the read/write "addresses" are
  • 0xA0(W)
  • 0xA1(R)

Configuration Data

The ASIC is configured via various memory addresses in the EEPROM, documented in the chip's datasheet. Some are single-byte, others two-byte little-endian. Little-endian means that the least-significant bits (LSB) of the 16-bit value are in the lower address followed by the most-significant bits (MSB) in the higher address; for example the value 0x1770 will be stored in the EEPROM as 0x70, 0x17. Aside: the 0x convention means a base-16 number (hex), similarly a b suffix usually infers base-2 (binary).

Aside: there's some misunderstanding and lack of clarity on the various information sources out there. Just because the ASIC datasheet implies something doesn't mean the UT210E hardware supports it. e.g. RS-232 output: the UT210E actually has this enabled in the ASIC's config but the hardware just isn't present (ref). Despite that you'll see people simply writing a "magic value" 0xCE to the config address 0xFA, blowing away the other configuration bits at that address (the UT210E OEM value is 0xEF). The value 0xCE was presumably chosen from an article on a different meter that uses the same chipset. As always, take everything with a grain of salt; YMMV.

Interesting Addresses

The following are some of the interesting addresses from the datasheet, and the OEM values for a DTM0660L device.

16-bit (two-byte) values are little-endian, see above.

|Address |OEM Value |Description | |--- |--- |--- | |0x10-0x11 |0x1770 |full range (6000d = 0x1770; 8000d = 0x1F40)| |0x12-0x13 |0x0898 |range switch upper (0x0898 = 2200d; 0x1838 = 6200d)| |0x14-0x15 |0x00BE |range switch lower (0x00BE = 190d; 0x0244 = 580d)| |0x1C |0x0A |current range warning current (0x0A = 10A)| | | | | |0x50-0x57 | |current calibration data, 2-bytes/range| | | | | |0x80-0xBF |- |"Measurement functionality setting" - operation of the selector switch and Mode button (see below)| | | | | |0xFA |0xEF |bitmap: button/backlight function and pin config, incl. enable/disable RS-232 - though not supported on UT210E| |0xFB |0x0F |Time before auto poweroff, minutes (1-255). Default: 15 minutes. 0: auto poweroff disabled| |0xFC |0x0F |Backlight on duration, seconds (1-255). Default: 15 seconds. 0: backlight stays on.| |0xFD |0x80 |bitmap: incl. b3..0 = low voltage power off d