This mod based on ability ES51922 chip (the brain of UT61 series DMM's) to control backlight of display.
Here you can to see how it working UNI-T UT61E DMM Backlight via sensor control - YouTube
Now if you are going to built this project, the several important points:
1. Strictly avoid any wires placed near sensitive input components. See picture.
2. Clean up you sensor chip assembly from any flux residues. Even no-clean flux not allowed to stay here.
3. Resistor R2. This should be adjusted to supply your LED's with proper amount of current. The value shown (33ohm) in couple with AMS1117 LDO will give 18mA through LEDs.
4. Photocuplers. Used to decouple DMM circuit from noise coming from sensor chip. Try to get LTV-817B, LTV-817C or LTV-817D.
5. Chip U3 on schematic is AMS1117-5.0, but any 5V output LDO can be used.
6. For wiring or PCB layout of sensor controller please follow all recommendations given in datasheet.
Here you can to see how it working UNI-T UT61E DMM Backlight via sensor control - YouTube
Now if you are going to built this project, the several important points:
1. Strictly avoid any wires placed near sensitive input components. See picture.
2. Clean up you sensor chip assembly from any flux residues. Even no-clean flux not allowed to stay here.
3. Resistor R2. This should be adjusted to supply your LED's with proper amount of current. The value shown (33ohm) in couple with AMS1117 LDO will give 18mA through LEDs.
4. Photocuplers. Used to decouple DMM circuit from noise coming from sensor chip. Try to get LTV-817B, LTV-817C or LTV-817D.
5. Chip U3 on schematic is AMS1117-5.0, but any 5V output LDO can be used.
6. For wiring or PCB layout of sensor controller please follow all recommendations given in datasheet.
Attachments
Nice work Tolik! Looks great. Note that there are other features/mods you can do on this meter.
Such as:
Quite frankly, this meter is one of my favorites. I really feel like Uni-T has been brilliant at hitting certain price points under $100. It's hard to find much better in these price ranges, even used. That being said, they have had LOTS of duds too. When they get it right the meter is an amazing value, when they get it wrong (UT61D for example) its just another budget meter for the scrap pile.
My favorites from them are:
Such as:
- Low-Pass Filter True-RMS (blocked in the USA due to Fluke patents)
- some features related to Hold/Max/Min
- turning on and off the PC link (Uni-T stupidly made PC link on all the time which blocks the Auto-Power off)
- Upgrading the input protection. There are spots for sparkgaps, which are unpopulated.
- external voltage reference (the pads are on the board, just unpopulated).
Quite frankly, this meter is one of my favorites. I really feel like Uni-T has been brilliant at hitting certain price points under $100. It's hard to find much better in these price ranges, even used. That being said, they have had LOTS of duds too. When they get it right the meter is an amazing value, when they get it wrong (UT61D for example) its just another budget meter for the scrap pile.
My favorites from them are:
- UT136A/B/C (D is no-go in the USA because NCV only works for 220V systems). At <$20 it's far and away the best meter in that price range. It's nothing amazing but at $20 its reasonably accurate, reasonably safe, well-built and has a great number of features
- UT139C - A real competitor for the UT61E. Slightly cheaper, lower resolution, similar accuracy specs, lots of other features that the hobbyist may like. Such as temperature, NCV, backlight, Variable Freq Drive measurements, up to 1GOhm input impedence, etc.
- UT61E - This is discussed ad nauseum above.
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Hi,
I saw a mod of either additional min/max function, but I didn't understand what this exactly doing. I have Peak function working...
LPF True-RMS, good value, but I bought my DMM from Honk Kong, so its should be ok.
external voltage reference + replace trimmer this is the way where I`ll go. I definitely thinking about something like LT1236 LTC6655 MAX6126 AD584LH. One of these should to do good job for external voltage reference. I'll be thankful if you point me to such mod description. For trimmer I think some Brouns polymer trimpot, for resistor - some low noise Panasonic 0805 resistor or similar should to be ok.
I saw a mod of either additional min/max function, but I didn't understand what this exactly doing. I have Peak function working...
LPF True-RMS, good value, but I bought my DMM from Honk Kong, so its should be ok.
external voltage reference + replace trimmer this is the way where I`ll go. I definitely thinking about something like LT1236 LTC6655 MAX6126 AD584LH. One of these should to do good job for external voltage reference. I'll be thankful if you point me to such mod description. For trimmer I think some Brouns polymer trimpot, for resistor - some low noise Panasonic 0805 resistor or similar should to be ok.
UNITREND UT61E service pack 1, hack, improvements, new features This topic discusses how to do several of the mods.
All UT61E have this feature disabled. I think because this meter is OEM'd to several companies they just left it out rather than face accidental infringement.
This thread discusses temperature drift and modification of the Vref circuit.
UT61E drift and recalibration - Page 1
Sorry, you have misunderstood me. The meter has TrueRMS, it uses the Analog Devices AD737 TrueRMS ic. What it lacks is the Low-Pass filter on the TrueRMS input. This is a design that Fluke patented. LPF-TrueRMS is useful when you have a signal with large amounts of high frequency noise on top of it. For example, electrically noisy environments such as SMPS, Motor drive circuits, etc. It works by filtering out the noisy hash on top of the real signal so that the RMS converter is only reading the real signal. The ES51922 IC has this ability built in but it is not enabled due to the Fluke patents.
Datasheet for the ES51922 IC
Schematic for the UT61E
The multimter should be more accurate than your scope.
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To enable LPF mode, I think you set FC5 low (pin 118) and then press the key button (pin 99) for 1 sec. Key I think is the blue button but I'm not 100% certain on that.
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This need to check. If I need set pin 118 low, and than just to press KEY once for enter AC mode, than press KEY for 1 sec for LPF... It's not a big deal. I'll check it on weekend, and replay result.
Now external V reference. I just researched the components that I can get locally.
If I going to implement comp circuit + LT1790ACS6-1.25#TRMPBF V ref, the cost of parts coming to $60-70. LTC6655BHMS8-1.25#PBF based reference will cost $17 - 20 more. Did you tried to build such V reference ? What is you impressions of DMM`s behaviour with this mod ? Is the improved accuracy wroth to spend $60-80 for it ?
Now external V reference. I just researched the components that I can get locally.
If I going to implement comp circuit + LT1790ACS6-1.25#TRMPBF V ref, the cost of parts coming to $60-70. LTC6655BHMS8-1.25#PBF based reference will cost $17 - 20 more. Did you tried to build such V reference ? What is you impressions of DMM`s behaviour with this mod ? Is the improved accuracy wroth to spend $60-80 for it ?
Don't forget that some companies give samples. Honestly, with this meter no it's not worth spending that much.
My vote supports this concept too.
Even if you paint it gold, it engine will always be short about reliable and high quality measurements.
UNI-T in our days seems as plain toy maker in comparison with the offerings of other vendors.
You and I always disagree on this. The UT-61E is far from a toy, it's not a Brymen/Fluke/Agilent/etc. but not every situations calls for that. I have two of these meters and love them for what they are. I know their limitations and downsides and use them within an area which they are very capable. I know they don't meet safety regulations (though the ones sold in Europe (UT61-E G/S) are better. At the end of the day, if you know your tools, it is a great device. For low voltage work, it is a phenomenal data logging meter.
Hi Tolik.
Great mod!
I'm planning on doing it in a similar way but I have some questions:
You're using the photo coupler to separate the touch sensor from the chip but it's still connected to 9V. Isn't it bad to have the noise generated by the touch sensor on the meter's voltage supply?
Why use the ES95022 at all? You can use the 9V to drive both your touch sensor and the LED's so there is no need to use the chip. The only difference is that it beeps when you switch on/off the backlight.
Hope you can answer my questions.
Hello Nisei,
From the other side, UNI-T will never be like Fluke or Amprobe ...
My circuit takes voltage from the battery terminals, so noise of the sensor IC is held maximally far from the sensitive loops. Of course you can to add either inductors or even LC network to be an over confident. But my DMM, with that mod, as is, working well.
From the other side, UNI-T will never be like Fluke or Amprobe ...
It native controls the LEDs ON time, and ON/OFF functions.
Tolik, how much current is this circuit drawing without the LED's being lit?
The voltage regulators and sensor are constantly on so I think even with the LED's switched off it's drawing maybe 3 times as much current as the meter normally does?
22,000 counts under 50 bucks, yes please
for me the constant refrain of "lacking in safety" becomes annoying.
Most of those mega safety features are for the mindless idiots out there. No I'm not going to be blindly switching between functions or inputs when checking a fuse panel. I wouldn't use anything but AC V anyway. Ive checked power drops into houses using a HF $4 special before, so there. was I careful you bet. If im checking HV or high power i'll probably spring for a dedicated probe and / clamp on for that job. e.g. this meter is for hobbyists not drunken master electricians
for me the constant refrain of "lacking in safety" becomes annoying.
Most of those mega safety features are for the mindless idiots out there. No I'm not going to be blindly switching between functions or inputs when checking a fuse panel. I wouldn't use anything but AC V anyway. Ive checked power drops into houses using a HF $4 special before, so there. was I careful you bet. If im checking HV or high power i'll probably spring for a dedicated probe and / clamp on for that job. e.g. this meter is for hobbyists not drunken master electricians
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