Wednesday, 2 April 2014

A new graphic display for a Fluke 8050A multimeter

Filed under: Uncategorized — Michael @ 17:47

In a previous post, I described my take on a new LED display for a Fluke 8050A digital multimeter. While gathering information about that project, I ran across a really fine upgrade at Ken’s Electronic Projects, Fluke8050A Hi Res Display, using an LCD graphic display. Well, I have since picked up another Fluke 8050A and, with Ken’s work as inspiration, this time I thought I would give it a new graphic display.

More than just 5 digits

The Fluke 8050A is really quite a capable instrument. It measures not just voltage, current and resistance but also decibels (at various reference impedances) and conductance. And it has a relative mode. Unfortunately, there’s only a little symbol for REL and dB, so you have no visual indication of the relative offset or the dB reference impedance or even what unit you’re measuring. So, I went into this with the goal to display these bits of information as well the value being measured. Another goal was to leave the Fluke meter completely unmodified. I think I achieved these goals pretty well. I’ll let the photos tell most of the story.

Pictures tell the story

Here is the meter in simple voltage mode. The background is dark green and the digits are white. (I still need to come up with something to hide the edges of the display.)
IMG_0001

This shows the meter in relative mode. The relative offset voltage is displayed at the bottom. For all of the unit indicators and relative values, I used color-coding that follows from the Fluke panel colors. V is light green, A is light red, Ω is yellow, S is grey, dB is light blue and Z is a darker blue. (It’s subtle and doesn’t show up that well in some pictures.)
IMG_0002

This is in dB mode. The reference impedance is also displayed.
IMG_0004

Of course, dB works in relative mode as well.
IMG_0005

This shows the low-battery indicator. It is actually in red. By the way, the line under the main display turns red when the Fluke sets the high-voltage indicator.
IMG_0009

Construction

The 8050A is not modified in any way with one small exception (I’ll point that out when we get to it). The LCD display module is removed intact. All of the signals needed (except one) are available at the microcontroller in the Fluke.
In order to not have to solder anything to the meter, I built this little piggyback carrier to bring out the Fluke’s microcontroller pins.
IMG_0018

IMG_0019

For the extended processing I used an Atmega32u4 breakout board from Adafruit. (I removed the two LEDs from the board. First, because there’s no need to light up the inside of the meter. Second, and more importantly, I needed the PE6 pin as an interrupt and not as a communication monitor.)
IMG_0023

The breakout board is mounted to a bit of perf-board with pins to match the sockets on the piggyback board. There’s an 8-pin connector to the display and the low battery sense. Yes, that is actually wire-wrap.
IMG_0025

The display is also from Adafruit, their 2.2″ TFT LCD display. As Ken mentions in his article, the breakout board for the display is too big for the opening in the meter. I carefully made the board the same size as the display. I glued a connector to the back of the board after wiring it to the appropriate locations. (The breakout board supplies 5V/3.3V level-shifting and a 3.3V regulator for the display power.) Also, the SD card reader was removed. The CS signal is hard-wired to ground on the LCD board. The backlight PWM control pin is not used and neither, of course, is the SD card CS pin. This leaves just 5 lines RST, DC, MOSI, MISO (not really needed) and SCK in addition to GND and 5V. These seven wires, together with the low battery signal, plug into the 8-pin header on the piggyback board.

IMG_0012

The display is mounted to a bracket that fits the screw mounts for the main circuit board. (This is not the final bracket. I needed to move the display farther forward to avoid having to trim the Fluke display board.)
IMG_0015

Here it is all together. Well, almost.
IMG_0026

As I mentioned, the Fluke is unmodified. That is, except for the addition of one header pin soldered to the display board. My unit has the battery option and the low battery signal is generated on the display board. Fortunately, there is a via in the routing of this signal to the original display driver chip. You can see the pin in the picture above between U14 and U15. The black wire from the piggyback board attaches there.

Software

I am still fine tuning the software and will post it here shortly. I may make a few changes to the font and symbol bitmaps, as well. If you can’t wait, add a comment and I’ll get back to you.
I have been using the meter with the new display for a little while now and feel pretty confident that the software is in order.

You can download the project files here (last updated 7. August 2015).

Unzip the file somewhere. Move the Modified_Adafruit_ILI9340 folder to your Arduino libraries folder. This is the Adafruit_ILI9340 display library but stripped down to just what is needed. I did this for size and speed. The Arduino sketch folder is named TFT_8050A. Just move this entire folder to your Arduino directory. The folder contains the .ino file and the header files that define the character and symbol bitmaps used.
Be sure to select the Arduino Leonardo board in the Arduino environment if you are compiling the sketch there.
At some point, I’ll get a description of the code here. If you have any questions, you can post a comment or send me an e-mail (the address is in the .ino file).

Conclusion

This is just intended as a better-than-original display replacement. The Fluke is a solid measurement front-end and with a bit more effort you could extend it, using added computation, even further. You could display a graph showing trends, for example. With USB support (the Atmega32u4 has it) you could provide logging. I have no need for these things and I’ve wasted, uh, invested enough time in this already. As good as it is, the 8050A is old-school, with big, physical switches, no auto-ranging, etc. Still, it does the job and this one is now back in service, maybe for another 30 years.
Thanks for your interest. Your comments are welcome.

UPDATE: 05. Feb. 2017
Thank you all very much for your interest in this project! Some of you have asked if a schematic is available and a couple have inquired about a kit. (I am sorry that for many of you, this update is rather late.) In fact I did look into developing an upgrade kit but thought it would be too expensive to really make it worthwhile. I figured it would cost upwards of $60 and that was with little or no profit. Oh well.
Anyway, at that time I did create a schematic (no PC layout, though!) but kind of resisted posting it. It does not exactly represent the project described in the post (uses ‘raw’ parts and not breakout boards). And I thought it was best to derive a schematic from the pin assignments in the code.
But anyway, here goes. This is the latest version of the schematic I could find.

I’m pretty sure that this is correct but I can’t make any guarantees. I think I used the same pin assignments as in the code. If not, change either the schematic or code to conform.
Again, thank you all for your interest. It pleases me greatly that this project and my LED upgrade have inspired people all over the globe. Just to let you know, my meters are still going strong and get used regularly. I hope yours are too!
And if one of you ever does develop this into an upgrade kit, let me know. I have a couple more 8050As myself!

22 Comments »

  1. Hi.
    I’m interesting to you display project. You can sent me news about
    Very Regards
    Salvatore Lauritano

    Comment by Salvatore Lauritano — Wednesday, 30 April 2014 @ 5:25

  2. Congratulations for the idea, it is very impressive. I have a 8050A with the LCD broken and I like to do something like this, but I don’t know how to connect the Arduino’s pins to the 8050A. Is it possible to you to publicate the schematic?

    Also, I have a bunch of Arduino Megas and Nanos but none Leonardo, I wonder if I can use them for this project…

    Thanks in advance and congrats again.

    Comment by Alejandro — Tuesday, 13 May 2014 @ 21:35

  3. Thanks for interest! I have made the software available (link is in the post). Still working on a complete schematic. More soon.

    Comment by Michael — Monday, 19 May 2014 @ 16:14

  4. Hi, I was reading you from several months ago, I like your posts very much. I wonder if you can help me to fix this issue: I own a Fluke 8050A (without battery option), and it doesn’t switch on. I’ve found the failure, the power supply transformer doesn’t have any output voltage (referenced T1 in schematic). I have tested it out of the board. I have no idea of its values, and consequently I can’t find a replacement of it because the original is at least impossible to find. I’ve looked at the schematic but there isn’t any information about the output voltage of the transformer. Do you know the output voltages? Pin 10 is the common and pins 8 and 12 are the two secondaries. Thank you in advance and sorry for any inconvenience caused.

    Comment by Alejandro — Saturday, 31 May 2014 @ 10:38

  5. Hello Alejandro,
    The transformer in my non-battery version of the 8050A measures 30 VCT (volts center-tapped) or 15-0-15. It should be easy to find something that fits in the available space. The specification on the bottom says that the meter draws 4 Watts. Look for a transformer with a bit more power handling, say, 8 VA (volt/amperes which is more-or-less equivalent to Watts).
    I hope you get your meter back in service!
    – Michael

    Comment by Michael — Saturday, 31 May 2014 @ 15:33

  6. Hi, Michael. Thanks for your reply, you’re so kind. I have a doubt: How it is possible that there must be +13VDC in TP2 test point (after rectifier U29 and C16, in the input of the +6V regulator) if the transformer has 15+15 VAC output? According with this, there will be 30V AC x 1,4142 = 42,43V DC, isn’t it?

    Thanks again for your help.

    Comment by Alejandro — Saturday, 31 May 2014 @ 18:07

  7. Hi Alejandro,
    You’re welcome.
    I measured again and here are the values for one meter (this one is completely original and works perfectly).

    transformer 8-10-12
    14,8-0-14,8 (meter “off”)
    12,2-0-12,2 (meter “on”)
    TP2 +14,8
    TP3 +6,03
    TP4 -5,05
    TP5 -13,2
    A bit more info…
    The secondary resistance is 49,0 Ohms (8-12) but 21,4 on one side of 10 and 27,6 on the other.

    And here are the values for my LED-modified meter.
    transformer 8-10-12
    14,9-0-14,9 (meter “off”)
    10,8-0-10,7 (meter “on”)
    TP2 +13,5
    TP3 +6,13
    TP4 -4,97
    TP5 -10.2
    The secondary resistance is 47,5 Ohms (8-12), 20,6 on one side of 10 and 26,9 on the other.

    I don’t know that much about transformers, but it seems that the one in the Fluke 8050A is probably not for much current.
    Hope this helps.

    – Michael

    Comment by Michael — Saturday, 31 May 2014 @ 19:40

  8. Oh, thank you very much, this is much more information than I would have expected 🙂

    Certainly, the supplied transformer is pretty small and its output power maybe be very just to feed adittional electronics. If you experiment a lower voltage measurements in a LED-modified meter, maybe it means that the transformer hasn’t enough power and collapses a bit.

    But unexpectedly, your measures in the test points in the “LED” meter are in range with the schematic, unlike the ones in the “original” meter doesn’t. Is the LED meter recapped or so?

    I will try to look for a 500mA transformer, hope it works and can fit inside the box.

    Thanks again for your time and your attention.

    Alejandro.

    Comment by Alejandro — Saturday, 31 May 2014 @ 20:47

  9. Hi, Michael. One guy tells me that he has replaced the transformer with a 12 + 12V 3,5VA one and he says that it works perfectly. I am not sure in which transformer do I need, 12+12 or 15+15, but maybe I try a +12V and will see in what results.

    New transformer will be a 12VA (500mA) one, because there is enough space for it inside the meter and I want to have extra power to supply any possible replacement to the LCD display, either LED or TFT ones.

    I will take the opportunity to mount a fuse on the mains input as it is not included as you know (I don’t know why not it is, because there are space for it).

    I will report the results if you want.

    Thank you for your help again 🙂 🙂

    Regards,
    Alejandro.

    Comment by Alejandro — Sunday, 1 June 2014 @ 13:34

  10. Hi, Michael.

    I’ve connected a 12+12V 0,5mA transformer and the meter is alive!

    Secondary windings of the transformer measures:
    14,00V (meter “off”) each winding, center tap as common
    14,25V (meter “on”) each winding, center tap as common

    As you can see, there are no significative differences between switching on and off the meter, your measurements in these points are a little bit stranges (so many difference between on and off, it may be more or less equals). I think that your transformer simply collapses, it can’t do more power than needed (its my opinion).

    But all is not perfect, I have abnormal measurements on TP2 and TP5. Until I will do more deeper tests, I have a problem in supply zone:
    TP2 +17,83 instead of +13V !!
    TP3 +6,20
    TP4 -4,93
    TP5 -17.50 instead of -10V !!

    OK, thats another war… 🙂 But I want to give you my AC measures of the secondaries of the transformer.

    Best wishes,
    Alejandro.

    Comment by Alejandro — Sunday, 1 June 2014 @ 22:33

  11. Hi Michael,

    A very interesting and timely project for me, since I left my 8050 in a very cold place and subsequently it froze and destroyed the lcd.
    I made an attempt to compile your code, however I got
    “Modified_Adafruit_ILI9340.h:122:22: error: ‘prog_uint8_t’ does not name a type”
    I cannot find a declaration to this anywhere, would you be able to help on this issue?

    Thank you in advance,

    Frank

    Comment by Frank — Monday, 2 February 2015 @ 19:17

  12. Hi.
    A very interesting project. me now from the US is fluke 8050a with broken LCD . want to use your work on this issue. You completed the schematics for your revision / rework fluke 8050? ?

    Comment by Roman — Saturday, 24 October 2015 @ 11:59

  13. Help!!! The link for download the project files is broken!! Can’t download the files required..
    Thanks for you attention.

    Best wishes
    Danny.

    Comment by Danny — Wednesday, 11 November 2015 @ 23:02

  14. Oops, a typo in the last upload. Should work now!

    Comment by Michael — Thursday, 12 November 2015 @ 0:12

  15. Thank you, Frank.
    The issue was with the handling of program memory in the newer AVR GCC compiler. The software link in the post now has the updated code.
    (I have also contacted you directly. Thanks again for your interest.)

    Comment by Michael — Tuesday, 8 December 2015 @ 16:20

  16. Roman,
    Thanks for your interest. I have contacted you directly.

    Comment by Michael — Tuesday, 8 December 2015 @ 16:21

  17. Did you happen to make a kit for this?
    I have several 8050’s that I would like to use your mod on.

    Comment by Derek — Sunday, 3 April 2016 @ 20:32

  18. I have 2 8050A that are working perfectly and have good LCD displays, however, I would love to upgrade both to your graphical display. Is the schematic ready for this project?

    Thanks

    Comment by Rodney Gray — Wednesday, 28 September 2016 @ 12:36

  19. Hello Michael,

    Thank you for your nice work. last weekend I bought 3 of those fluke meters for EURO 15 each. One seems to be working fine and the other two have a dead display. One has the battery option, with batteries that just have been started leaking.

    I like to give it a try to put in an LCD, and follow your solution, however I could not find the schematics on your site. Could you publish these as well please?

    Thanks and regards,

    Ewald

    Comment by Ewald Burger — Monday, 7 November 2016 @ 7:20

  20. Hello..
    really good work
    can you publish other information or schema ?

    tnx

    SteF

    Comment by SteF — Saturday, 4 February 2017 @ 17:03

  21. Hello there. Great job. I am not sure the fluke 8050A is worth the effort. I have grabbed a scrapped on from the hazardous waste bin at work. It needs some repair (dead). I might want to pursue you display project just as a hobby, but I never seem to have time.

    Your schematic. May I ask, it sure looks like Circuit Maker 2000? I still use that program too; even in Windows 10.

    Comment by David Kuhn — Friday, 31 March 2017 @ 17:49

  22. That was done in KiCAD. And, of course, you’re right about the effort. But it was a great way to learn more about microcontroller programming and I got a nice meter out of the result. I should say that the meter was in excellent shape other than the display, though.
    I only did the schematic as a first step to making a PCB. I had the idea that this might make a nice kit for sale. There are a lot of 8050a’s out there with bad displays that are otherwise working. But I decided it would not be economically practical.
    Thanks for taking a look.
    – Michael

    Comment by Michael — Friday, 9 June 2017 @ 9:52

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