UT61E mod with ATMega328 - Page 1
Forum section: electronics / testgear

author: morato
author_rank: Newbie
timestamp: August 19, 2018, 06:51:30 pm
content: Hi,My name is Paulo and I am Brazilian.Last year I decide do a mod on my 2013 UT61E. I was frustrated with not precise resistor measurement, calibration degradation, no auto power-off and non existent backlight. I am hobist and work in this project and others only in free hours.New Functions:- No trimmers to calibration volts or currentNote: The choice of resistors have be to preserve proximityoriginal reference value because is not possible to calibrate the PEAK function.In my multimeter values for DC are 7k5 (original) to gnd and 390R (~VR1 value)and AC are 3k connected to C12 and 5k6 connected to R14 (~VR2 values).All resistors are 1% 20ppm. (look schematic)- Ohms can be high accurate depending only the your calibration references- On power-up, show UT61E in display- On power-up, press Yellow button to enable RS232. The symbol is displayed- On power-up, press Yellow and Blue button in same time to enter incalibration mode (CAL in display)- In calibration mode, select function in rotary switch, press yellowand blue same time (<1s) to enter in ADJ mode (ADJ in display)OBS: Adjust mode only is permitted when in manual range. If auto range,"AUtOr" is displayed and advertise beep- In adjust mode, press yellow to decrement or blue to increment in0.00001 correction factor- In adjust mode, press yellow and blue same time (<1s) to exit adjustmode (Func in display)- In calibration mode, but not in adjust mode, press yellow and bluemore than 1s to save calibration data (SAvE in display)OBS:Only volts dc or ac, current dc or ac and ohms are possible tocalibrate- In normal operation, press yellow and blue in same time (>1s) topossibility usage the Low Pass Filter. After, blue button to enable.(AC symbol flashing)- Press blue button >1s to Max/Min function and press blue <1s tochange between max, min and current value. Press blue button>1s to exit- Original pc connection capability was maintained- Auto power off- Backlight with auto off after 60sES51922 Characteristics:- If uPLSD is enabled, RS232 can set only in power-up time- LPF only can set if SLACDC is set- Display content can set ~100us after data is received- Original sleep consumption is ~230uA and in running mode is ~3mA.Additional microprocessor add 5uA in sleep and 1.5mA in runningmode. The consumption fault above the nominal is because the 3v regulator- The ADC not have a good linearity and this mod not correct this, butif dedicate any work in the software you can get more accuracy (formula in conversion)- I try get more stability in display update, but any flicker occur whensend uPLSD data. I believe this a "characteristic" of chipOptional:- Caddock 1776-C481 resistor array- LT1790ACS6 to 1.25V reference- Epcos SDG 1400V for protection- Probes from Probe Master- Replace poor input jacksList off materials:Control board (all resistors are 805 5% 200ppm):1x Atmega328P-au2x resistor 100R (backlight)1x resistor 10k (reset)1x connector array 2x3 (CSP)1 meter enameled wire 32AWG1x 3x3cm fiber class boardMultimeter (all resistor are 805 1% 20ppm):1x LT1790ACS6-1.25 (U4)*1x Caddock 1776-C486 (R7 to R11 and R34)***1x resistor 390R (VR1)1x resistor 3k (VR2)1x resistor 5k6 (VR2)1x resistor 12k (R52)*1x resistor 10k (R53)*1x resistor 100k (R51)**1x resistor 1M (R51)**1x capacitor 10u/10v (C50)** optional to use external and more stability voltage reference** 100k and 1M in parallel to 90k9 to get best tempco (You can use original 90k9)*** this is expensive component (US$23 in digikey) and after compare with original array, is not really necessaryI don´t have an video to post now, but I will make to show new funcionalities. All can modify and contribuit to aprimorate code and project, only condition is to share here.I do calibration with refere provides byhttp://www.voltagestandard.com/and comparations with my HP3478A and Keithley 196.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 21, 2018, 08:08:09 am
content: Woah radical work you had some fun putting wires on the cpuhttp://asknotes.com/2017/08/25/ut61e-digital-multimeter-schematics-and-integrated-circuit-datasheet/

author: morato
author_rank: Newbie
timestamp: August 23, 2018, 03:39:45 pm
content: I hope it's useful. Thanks