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Old 10th May 2018, 4:52 pm   #1
WaveyDipole
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Default Fluke 187 IR Interface

Some time ago I acquired a Fluke 187 DMM. Unlike the 189 which has built-in logging memory, the 187 needs to be connected to a computer to provide logging and this this requires a USB infrared adapter. I had wanted to connect the Fluke to the PC but a genuine Fluke cable and software were by no means cheap. The cheapest Fluke IR adapter I could find on eBay was £45. However, also required was the FlukeView Forms software, which is a commercial product and costs around £200. There is also a 3rd party PCB available for around £17 from Russia, but I decided to take the DIY approach and build my own interface. For logging meter data on the PC, the open source Sigrok software is freely available to download and use.

It is possible to find a number of designs online. These usually involve a FTDI FT232RL chip for the USB interface. A complete FTDI FT232RL USB cable can be purchased on eBay for £7-8 and has six outputs, including V+, Gnd, Tx, Rx, RTS, CTS. The FT232RL chip does have the facility to drive indicator LEDs, but the connections for these are not provided at the cable end. Designs usually seem to involve an OP amp to drive the IR LED and reeiver IR transistor. Some individuals have produced their own PCB and used SMD components for the job which is neat. Getting a PCB made would be of interest if I could get them made cheaply enough, but in the UK, unlike in other parts of the world, this does not seem to be a very cost effective option. I therefore looked for a way to make the interface using more traditional means. Rather than simply copying the OP amp designs, I decided to design my own interface using readily available discrete components. Having seen a photo of the internals, apart from the USB IC, a couple of transistors and some resistors is all the genuine Fluke interface seems to use, so how difficult could it be? I initially used a prototype board to experiment with and it turned out that an interface could be created relatively simply.

The IR devices were obtained from a UK supplier:

IR Transmitter: Vishay TSAL6400 (https://www.bitsbox.co.uk/data/optos/tsal6400.pdf)
IR Receiver: Vishay BPV10NF (https://www.bitsbox.co.uk/data/bp10nf.pdf)

The spacing between the IR devices in the meter is only 5mm. I used 5mm devices and it was just about possible to have them sit next to each other with a bit of shrink wrap over them, but it would perhaps have been move convenient to have used 3mm devices.

For the rest of the project I used a small project box acquired recently from Maplin, and transistors, LEDs, resistors that I already had available.

After a bit of experimenting on the prototype board, I came up with a circuit using a single BC327 transistor - see the first attachment.

CTS and RTS are not used. The interface can be tested using a terminal emulator such as PuTTY and setting the terminal communication parameters to 9600, N, 8, 1. By placing a spoon in front of the IR devices so that the signal from the transmitter is reflected back to the receiver, it is possible to determine whether the interface is working correctly. Characters typed at the terminal should be echoed back to the terminal.

Once this stage is reached, the interface an be tested with the actual meter. Care needs to be taken to align the IR devices correctly. If all is well, the meter should respond to the ID command with the characters FLUKE followed by model number, firmware version and serial number. The QM command should return the displayed reading. In order to work correctly with Sigrok, the IR devices must be optically shielded from each other to prevent echo.

I thought it would be a good idea to add transmit/receive indicator leds to indicate interface activity. This involved adding a couple more BC327’s, a couple of LEDs and some resistors. The updated circuit is in the second attachment.

Having completed the design an prototype on the breadboard, I procided to build it on a small piece of veroboard and house it in the case. Measurements to ensure a correct fit take a bit of patience. I found a piece of black plastic back that had been discarded and used this to make the base that slides into the back of the meter. This was glued using epoxy adhesive to the underside of the box. The PCB is mounted using a couple of metal mounting posts and the indicator LEDs were recycled from by bits box.

I have attached a PDF with more technical details and some instructions on how to connect and use with Sigrok.
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Attached Files
File Type: pdf Fluke187 IR Interface Notes.pdf (123.1 KB, 465 views)
File Type: pdf Fluke-Commands.PDF (132.4 KB, 499 views)

Last edited by WaveyDipole; 10th May 2018 at 5:08 pm.
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Old 10th May 2018, 5:36 pm   #2
WaveyDipole
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Default Re: Fluke 187 IR Interface

Some pictures of the interface under construction and the completed item.
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Old 10th May 2018, 5:40 pm   #3
WaveyDipole
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Default Re: Fluke 187 IR Interface

Connected to the computer and using Sigrok.
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Old 23rd May 2018, 9:47 am   #4
jez_145
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Default Re: Fluke 187 IR Interface

Congratulations and very well done on the interface project. It's always satisfying to overcome obstacles like this by coming up with your own solution plus I'm sure you learned a thing or two whilst doing so !

Two or three years ago I had a requirement to do some data logging like this, and ended up buying a UT71D multimeter on the grounds that I couldn't justify the cost of a Fluke 287/289 plus the optional extra interface and software - which all adds up to a pretty penny as you say. For what I wanted to do, this has worked very well and it has proved useful just having a second DMM, for some jobs, regardless the data logging aspect. The software that came with my meter is pretty rudimentary but it works ok and, most importantly for me, the data received can be exported to external files for further analysis using Excel etc. I might look further into the possibility of using the Sigrok software you mentioned - though a quick look at their website doesn't seem to include my model in the supported devices list. Still, there might be something suitable, possibly.

When I bought my meter, I planned on linking it to a PC for realtime logging. However, in practice, I tend to just use the meter in standalone mode, set the record interval, and let it do the logging by itself. I then transfer the results to the PC via the optical/USB link at the end of the session.

I have to admit that I have only used the logging aspect of my meter a handful of times so far. It's great for recording one measurement against time but it would be handy to be able to record more than one variable against time such as frequency and temperature, for instance. But, we're getting into more specialised data logging territory here !

I'd be interested to hear of any practical applications you have used, or plan to use, your interface for ? Indeed, if any other forum members use a multimeter for data logging please chip in.


Jerry
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Old 23rd May 2018, 12:03 pm   #5
WaveyDipole
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Default Re: Fluke 187 IR Interface

Jerry, thanks. I notice that the UT71C is supported:

https://sigrok.org/wiki/UNI-T_UT71C

Not sure how much difference between models in the series, but the UT71D is apparently a re-badged Temna which is also supported:

https://sigrok.org/wiki/Tenma_72-7732

I have only used it once so far while still in the prototype stage! I had a receiver that was cracking loudly after being switched on for several minutes. The noise was independent of the volume control. As a first step I wanted to see whether anything odd was happening on the power supply which could not be determined by taking one off readings, which indicated that the voltage was roughly correct. It occurred to me that logging might be able to tell me whether there was any change over time, which might be indicative of, say, a smoothing cap causing problems when getting warmed up. Logging was set up on first the positive then on the negative lines and observed as the crackling noise appeared. I could see the power supply come up to approximately the expected voltage on power on and stabilize with a bit of ripple but no obvious change when the cracking started. It was also interesting to see the voltage steadily rise/fall in a curve towards zero as the capacitors discharged on power off. Each trace mirrored the other so there seemed to be no problem evident with one particular side of the supply. Having ruled out the PSU a detailed look at the amp circuit then seemed to be be in order. In the end it turned out to be a small plastic transistor in the first stage just after the volume control which was confirmed through swapping parts between left and right channels. However, the logging seemed to be a useful first step.

As you say, the need for logging perhaps does not crop up that often, especially for just an enthusiast, so I didn't want to spend too much on an interface and software which I might use only very infrequently. However, it might still be useful to have to fall back on if the need arises. Designing my own using what I already had to hand seemed beneficial both by saving cost and gaining learning experience.

The 187 can display two parameters on the LCD screen in some modes, but there is only one output channel detected, so Sigrok only displays one measurement at a time. It does also export the graph to image file and there is an option to export the data to a CSV file, but in the version that I downloaded quite a while back (0.1.0), this does not work yet.

I would also be interested in hearing about any other practical applications for logging that others have come across as it would be worth bearing these in mind for future reference.

Incidentally, I discovered that if the indicator LEDs are included, the device also functions as a useful remote control checker. Simply connect to USB (no meter required) for power, point the remote at the sensor and press any button. If working, the receive LED will flash in response. I guess most on here will also be aware that many (though not all) mobile device cameras will show the remote control IR LED blinking.

Last edited by WaveyDipole; 23rd May 2018 at 12:15 pm.
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Old 23rd May 2018, 1:38 pm   #6
MrBungle
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Default Re: Fluke 187 IR Interface

Nice work. I much prefer seeing stuff like this than someone being mugged for £200 for the cable.

Actually Fluke's pricing of these extras drove me to buy a Keysight (U1241C) unit. I was expecting to have to buy the cable separately but it came with the meter. Was very happy. I doubt I'd buy another Fluke product again. Orders of magnitude better quality and value for money.

The Uni-T meters are pretty good on this front if you get the one with the USB cable. The serial cable is problematic as it doesn't work properly on the average laptop USB/serial bridge cable.

As for practical applications, I've done the following:

1. I have a TTi TF930 counter which is also PC connected so when I was playing with PLLs and huff puff circuits I was using it to plot frequency vs voltage.
2. Monitoring mains voltage over time.
3. Measuring temperature over time (U1241C has thermocouple support)
4. Slow speed precision oscilloscope (40Hz sample rate on U1241C)
5. Measuring RF power. I have a python script and a power sensor based on an AD8307 so you can get it to read the voltage and do a Y=MX+B calibration transform to get real power out.

Honestly I will never run out of uses
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Old 23rd May 2018, 2:14 pm   #7
WaveyDipole
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Default Re: Fluke 187 IR Interface

I have found USB-to-serial cables based on the CH340 chipset problematic, but no such problems with anything based on a genuine PL2303 or RTL232.
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Old 23rd May 2018, 3:39 pm   #8
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Default Re: Fluke 187 IR Interface

Keysight one is PL2303. Not had any problems with CH340 yet at least on Linux.
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