Backlight mod for UNI-T UT-61E

Discussion in 'The Projects Forum' started by flat5, Nov 14, 2014.

  1. flat5

    Thread Starter Active Member

    Nov 13, 2008
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  2. wayneh

    Expert

    Sep 9, 2010
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    Do you not want continuous backlight, or maybe a backlight that comes on in low ambient light?
     
  3. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    Thanks for your input, wayneh!

    For continuous I don't need a switch. Detecting the ambient light level is an interesting idea but I think it will involve drilling a hole in the meter.
    In that case I might as well install a switch.

    There is a You-Tube video of a solution where you bring your hand near the top of the meter and the backlight goes on. Do it again and the light goes off. It will also go off after 60 seconds. This is an elegant solution but requires quite the mod including a few SMDs and flying leads and cutting traces. Other mods mess with the 'Hold' or other functions of the meter.

    So what I'm hoping is that I bring a hand to the case in a specific (secret) location and the light comes on for at least 12 seconds without disturbing the meter circuitry.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Will you be using the existing backlight? I'm unfamiliar with this model but online photos seem to show it has one. I assume you'll use the existing battery.

    What about when the meter is off, I assume you don't want the light to come on?
     
  5. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    Good points. There is an off position of the main switch. I will grab power from the meter but that is not a major mod of the meter's circuitry. I hope. Looking at the schematic I see the battery at the lower right of the switch. The switch wiring however is a complete mystery!

    I believe I will have to buy the correct LEDs and provide them with no more than 20ma.

    Copy of uni-t_ut61e schematic.png

    Edit: How did you wire the cat's eyes?
     
    Last edited: Nov 14, 2014
  6. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    There are alot of mods for that meter ... Led mod is a popular one and it built in the chip but just no button and led for it .. I was going to buy one and mod it myself but found I could buy a Fluke Series II 87 meter for about the same price and its already done ... Also its a lot safer and will last past my lifetime if taken care of and was built with real quality vs cheap Chinese crap...

    I will find some more info for you later ...
     
  7. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    I have looked around the net. Most of the mods can be found at
    http://mjlorton.com/forum/
    and
    http://www.eevblog.com/forum/
    and
    http://www.diyaudio.com/forums/equipment-tools/257668-uni-t-ut61e-dmm-backlight-mod.html
    and You-Tube

    A quick look tells me the Fluke Series II 87 starts above $700.
    I paid less than $40 for my meter which if used properly will last for many years.
    This meter even has a good frequency counter that works beyond 200Mhz!
    With a simple mod the calibration will be improved in the long term.
    (replace a pot with a resistor or two and a smaller pot.)
    I might do that one.
    There is provision for adding spark gap protectors. Might do that one too.
     
    Last edited: Nov 16, 2014
  8. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Sorry I meant A used Fluke 87 .. I paid like $70/bucks for mine and looks almost new.... Oh OK I was not aware of all the mods .. Once I figured the price difference and time it takes and the possibly of damage I spent the extra and got a Fluke .. Make sure to replace the glass fuses with HRC fuse...
     
  9. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    You got a great deal on the Fluke :)
    They look like ceramic fuses but not the best type available. If I can find better spec. ones that fit the fuse clamps that would be great.
    I won't be subjecting the meter to high voltage or current.
    I am just a hobbyist but I have 9 DMMs, mostly very cheap ones, and if I need to measure something like 600 volts I'll blow one of them up :)
    For AC current I have a clamp meter and I should look for a .1 ohm high power resistor to add to the inventory anyway.
     
  10. Cal Rico

    New Member

    May 1, 2012
    15
    1
    Hi,
    I like where you started. "hacking" into DMM and adding a LED light. Somehow this thread meandered into pricing out a Fluke.
    This thread now interest me into adding a light to a low-end Mastech DMM. I no not desire to find an alternative DMM. I now really want to try to modify an existing DMM. The two models I would consider are a MY68 or a MS8222H.
    1st has no light at all. The 2nd has a light that turns off in 5 seconds. It also has a small current drain problem when it is off.
    Somewhere above there was a mention of the HOLD button. To me that seems like a good switch to use. I have always found the HOLD feature pretty useless, except on Clamp meters.

    I will look at the youtube videos that have been mentioned..IF a link or by name would help.
    I hope we may continue this thread with several ways of adding or improving a light on a DMM
     
  11. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    I'm thinking of a cmos 555 timer and a way to make the trigger very sensitive. Maybe using a fet open gate connected to foil to trigger the 555. If it will sink a little less than 20ma with no problem then just run the leds in series from the battery with a series resistor. If not, add a transistor.
    Mainly, leave the meter circuit alone.
    I should start with experimenting with the FET touch switch.
    Also I need to track down the correct LEDs.
     
  12. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Look scooter calm down .... Also stop Thread jacking and start your own thread .. I could see posting if it was the same make or model but its not... Sorry I was not suggestion a different meter but just mention what I did .. Cause I was going to buy a Uni-T 61E and I really wanted it but when I realized I could buy a meter that is 100x times better than the Uni-T for about the same price then it was a no contest decision ... I would still love a Uni-t meter but I have A Fluke 87 and 77 series and really have no use for it...
     
  13. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    I would try different color LEDs and see what would work for you or like .. Personal I would use some kind of button verse a touch sensor cause I would have to have a backlight keep coming on and off everytime I adjust the meter or change setting ..
     
  14. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    Also thinking of a reed switch and magnet or a mini slide switch.
    The sensor could also be used with a flip flop to turn light on and off.
    There by keeping the light on as long as wanted.

    I like the clever mod to turn the serial port on only when the adapter is plugged in.
    That can be done optically or magnetically. It would save battery power and provide auto off, if wanted.

    Probably the most important mod is replacing the voltage calibrate pot with a smaller value pot and two resistors. This should improve the drift problem.
     
  15. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    That sound like a bunch of good ideas but you have to see what works for you and what you like ...I would add the led to the auto off feature just to make sure you don't leave it on and kill the battery's all the time.. As far as changing the pot I am not sure how that's going to work or why but I would just leave it and just have some kind of high performance voltage Reference and that would make sure your other meters are within spec.. Which would be a neat project for the guys here to build or I might play with some kind of setup and post my build ?¿?
     
  16. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    I finished a version of the UT61E backlight.
    I used 2 SMD 3528 LEDs. They came in a roll of 300 for just over 3 Euros.
    A 1.2k 1/4watt carbon film resistor and .3mm enamelled copper wire plus some hot glue were also utilized.
    As the backlight draws over 2 ma the battery is sourcing twice the current now.
    I think I can live with that. I'll see.
     
  17. Cal Rico

    New Member

    May 1, 2012
    15
    1
    Hi,
    Sorry if I may have"thread hijacked" here. The two meters were just examples regarding adding or improving the back light in a meter. My thinking was if you can do it with one meter then it could be done with most meters. Regarding what I said about the Fluke seeming "off-topic" i was referring to the part about pricing. I apologize, as I did not catch that buying the Fluke was about an alternative solution and correctly on topic.

    Perhaps mentioning my DMM models was unnecessary and inadvertently misleading. I have unintentionally not shown respect for the suggestion of getting a fluke as an option to this thread. I was wrong.

    I sincerely apologize about this error. I really have trouble with being helpful in forums. Perhaps I should just be more succinct and more focused.

    Coming back to this thread and finding that flat5 came up with the solution of slipping a 555 timer is great It is also a great solution.I would think, for my own DMMs.

    Thanks Again flat5! great idea, I will try this too!
     
  18. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    Cal, if you do use a 555 as a touch switch successfully I'd like to hear about it.
    I played with the touch switch I mentioned in post #1 and it may have worked for my situation.
    If you just want to have a backlight and can tolerate an added current of 2ma the LEDs SMD 3528 work well.
    Of course you can drive them harder.
    My meter was ready for the lights. It already had the panels for it.
     
  19. Nisei

    New Member

    Feb 16, 2015
    7
    0
    Nice to read you succeeded. But after mentioning several different ways to trigger it on/off you don't tell us which method you've used?
     
  20. flat5

    Thread Starter Active Member

    Nov 13, 2008
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    I do not turn the light on/off. It is wired to the main switch. Turn the meter on and the display stays lit enough to read it.
    It draws ~2ma. The meter draws about 2ma. The whole instrument draws less than 5ma. The 9v battery has not been replaced yet. I buy 2 alky batteries for 1.89 Euros.
     
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