EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: WaveyDipole on March 14, 2018, 04:08:14 pm
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I have read a number of threads on building an IR interface cable for my Fluke 187 including these here:
https://www.eevblog.com/forum/testgear/fluke-87iv-please-whisper-in-my-ir-p/ (https://www.eevblog.com/forum/testgear/fluke-87iv-please-whisper-in-my-ir-p/)
https://www.eevblog.com/forum/projects/fluke-187-ir-cable/msg956662/#msg956662 (https://www.eevblog.com/forum/projects/fluke-187-ir-cable/msg956662/#msg956662)
Also this site here:
http://kimboricha.blogspot.co.uk/2013/12/build-usb-to-fluke-189-irinfrared.html (http://kimboricha.blogspot.co.uk/2013/12/build-usb-to-fluke-189-irinfrared.html)
It seemed to be a fairly trivial task but I have run into difficulty. I am aware that the first thread discusses IRdA which is different and works with the Fluke 87IV and the author eventually resorted to using an Arduino to solve this problem. However, if I understand correctly, the Fluke 187 uses basic serial comms so one of the basic analog circuits should work with this meter.
I purchased two pairs of 5mm IR receiver transitor/IR transmitter diode devices off eBay and tried building the first circuit in the first thread which has no OP amp, just a simple arrangement of IR devices, a limiter resistor for the IR diode and bias resistor for the IR transistor. Initially I used a cheap CH340 based USB to UART adapter which I had to hand and it duly fried along with the transmitter LED. Puzzled but not deterred, I then tried the second one with the transmitter LED only and with the same result. I figured the cheap adapters were evidently not up to the job so ordered two FTDI FT232RL cables. These have a USB plug at one end and outputs for 5v, Gnd, Tx, Rx CTS and RTS at the other end. I figured this should make for an easy solution, but so far I have had little success with these as well.
Using the same cheap IR transimtter diodes and receiver transistors, I started with the simpler circuit without the OP amp and built it on a prototype board. The transmitter seemed to be working - for example when I substitute a visible light LED it flickers when I type characters. I had to change the limitier resistor from 220ohm to 56ohm as the transmitter LED draws 60mA rather then 20mA or so. Probing the Tx line on the FT232RL I do see the output on the scope at about 4v and can decode the characters being sent with a serial decoder. I can also see the signal when probing at the junction of the limiter resistor and the transmitter LED. There is a faint visible flicker on the IR LED when viewing it with a mobile phone camera.
The receiver is wired exactly as per the diagram and I have tried both a single and two 1k resistors in series, but on the scope the received signal looks very weak by comparison. I do see some spikes but I have to have the remote practically touching the receiver to get a sensible amplitude on the 2v per div range. Since remote controls are usually 38khz modulated this obviosly does not translate into any sensible characters at the terminal, which is only to be expected, but I do get some random characters occasionally.
Placing a spoon in front in order to reflect the transmitted signal back to the receiver does not echo any characters back to the terminal, so I am effectively stuck at the first hurdle. I also tried adding an OP amp (using an NE5532P and RC4558 that I had to hand) as well but this gave me no output and I then realised that 5v is too low for the operating voltage so it looks like I will have to order an LM393.
I am wondering whether the cheap LEDs are part of the problem and whether, in fact, the specific IR devices that were mentioned in the thread are critical? One of the posts mentions that it will work with '880nm or 950nm' wavelength LEDs so I figured it would not matter so long as the series resistor is correct for the operating current required.
I am also unsure how to enable IR on the Fluke 187 as this does not have a logging function like the 189 and just bleeps at me when I select logging. Its is supposed to be logging capable, it just doesn't store data onboard. The manual seems to assume the 189 model. I am not otherwise seeing any activity on the sensor with the phone camera.
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I am also unsure how to enable IR on the Fluke 187 as this does not have a logging function like the 189 and just bleeps at me when I select logging. Its is supposed to be logging capable, it just doesn't store data onboard. The manual seems to assume the 189 model. I am not otherwise seeing any activity on the sensor with the phone camera.
Hi, I have been trying to do the same, it is on my todo list now.
I think you cannot turn on the Infrared from the meter, it needs a special program to start communicating from the pc. Search for Fluke dmm meter interface program, not sure if it is free or something you have to pay for.
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I forgot to mention that when using the simple version of the circuit, although the IR LED does seem to operate, I get no response from the meter using any of the commands shown in the document here:
http://www.pewa.de/DATENBLATT/DBL_FL_FL187-9-89IV_BEFEHLSSATZ_ENGLISCH.PDF (http://www.pewa.de/DATENBLATT/DBL_FL_FL187-9-89IV_BEFEHLSSATZ_ENGLISCH.PDF)
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an ebay link : https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884? (https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884?) for 22$ usd free shipping ????
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Opto devce wavelenghth matching is important, of course you can get things to talk with poor matching but as you're going with the simplest setup it seems reasonable to start with matched wavelenghts.
Are your cheap LED / photodiodes meant to be matched? (A good thing if they are but still may not be matched to the Fluke)
60mA seems a little high on the LED considering that the FT232R data sheet states 24mA abs. Max. Output current if you are driving it from the TX pin.
On the photo transistor side you'll want the input to RX to cross under 1V and over 1.5V when switching.
A good starting point is to get the IR interface to echo itself correctly before trying to communicate with the Fluke.
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Just ordered one. Shipping of parts from Digikey is more expensive.
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an ebay link : https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884? (https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884?) for 22$ usd free shipping ????
That's an interesting find. Thank you for pointing it out. I think if the alternative IR devices that I have on order do not work out, then as a 'plan B' I might just order one of those.
Opto devce wavelenghth matching is important, of course you can get things to talk with poor matching but as you're going with the simplest setup it seems reasonable to start with matched wavelenghts. Are your cheap LED / photodiodes meant to be matched? (A good thing if they are but still may not be matched to the Fluke)
That makes sense to me, although as I mentioned, it had been claimed that it doesn't matter so I didn't take much notice when perhaps I should have done my homework. There is no indication whether the cheap LEDs are matched although I had assumed that they were. I have already ordered some additional devices that are matched at 940nm (TSAL6400 with LL-503PTC2E-1AD phototransistor, and also a BPW4 photodiode). These are of identical specification to the SI3317 and ST3811 mentioned in the other thread.
60mA seems a little high on the LED considering that the FT232R data sheet states 24mA abs. Max. Output current if you are driving it from the TX pin.
The SI3317 mentioned on the other thread has a 100mA forward current with a peak current of 1A although I cannot find a datasheet for the EL-7L so cannot confirm its rated operating current. Having had a look at the LM393 specs, I see that the maximum output current for this device is specified even lower at 20mA. Those ratings seem to be DC (continuous) rather than pulsed, but still that is quite a disaprity. The 220ohm resisor seems to be calculated to limit the current to around 20mA so presumably these LEDs are being under-driven in this circuit? On advice from the supplier of the LEDs I changed the resistor to 56ohm which now, in hindsight, was perhaps a bad idea. Does the close proximity of the interface to the meter mean that the lower drive current might still be sufficient? I did notice that on the original Fluke board shown in the photo, the output and input each has a transistor which I guess would allow for a higher LED drive current and amplification of the received signal.
http://3.bp.blogspot.com/-7GD2KAZQt30/UqB6pVldceI/AAAAAAAAAms/t2LByS3VEBc/s1600/Fluke_IR189USB_PCB_top.jpg (http://3.bp.blogspot.com/-7GD2KAZQt30/UqB6pVldceI/AAAAAAAAAms/t2LByS3VEBc/s1600/Fluke_IR189USB_PCB_top.jpg)
On the photo transistor side you'll want the input to RX to cross under 1V and over 1.5V when switching.
The 'high' state voltage was around 4.5v, but the negative going pulses rarely got as low as 1V. Based on this information, the input signal is obviously too weak.
A good starting point is to get the IR interface to echo itself correctly before trying to communicate with the Fluke.
Agreed and I will experiment some more but bearing in mind the information you have provided when the new IR devices arrive.
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The new IR LEDs and transistors arrived yesterday and today I have made some progress! They did not work in the original circuit so in order to provide sufficient current to the trasmitter LED I tried two different configurations involving transistors - one based on a single PNP transistor, the other on two NPN transistors. The PNP version did not seem to work, but the one based on the pair of NPN transistors did. I did some tests in LTspice first and have attached the schematics. I found a model for similar IR LEDs from Osram. The file has been renamed from .lib to .txt to allow the upload. In the NPN version, the first transistor stage reverses the polarity of the transmitted signal. The second stage acts as a switch to turn the LED on and off in response to the transmitted pulses. The series resistor limits the output current from the FT232RL to 20mA and I actually used a 270ohm resistor rather then the 220ohm, as that is what I had to hand and it worked just fine.
The receiver transistor picked up a clear strong response from the reflected signal and characters were now being echoed back to the terminal!
I then tried interfacing with the meter. Because this was a makeshift setup, the placing of the meter relative to the IR devices on breadboard required some trial and error but it didn't take long before I got a clear response to the ID request. I was then able to get some readings with the QM command. I also tried a few other commands which worked successfully, with the exception of the 'SF 19<CR>' command which is supposed to activate the backlight and which would not turn on.
As a final test, I tried the original IR LED, which, not being matched to the transmitter, not surprisingly did not work. I just wanted to be sure.
So it seems that the original IR LED was not suitable and, in addition, was not being driven by sufficient current. The next step will be to build the current circuit onto something more permanent and mount the board and IR devices with the correct separation into a suitable housing.
I would be curious to know why the PNP version of the circuit did not work?
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I don't have the Flukeview Forms commercial software but got it going with sigrok-cli and sigrok-meter today. Attached is the output from Sigrok Meter and a schematic of the complete working circuit. I think the issue with the PNP transistor version of the circuit was a faulty IR LED. The Vishay part works perfectly fine in the circuit below. In practice, the current (and hence IR intensity) was too high with the 20ohm resistor in series with the IR LED and when testing with the meter this caused echoing of characters back to the receiver even with optical shielding in place. Further experimentation showed that increasing this to 200ohm allowed the interface to function without any such problems.
IR transmiter - Vishay TSAL6400
IT reciever - Vishay LL-503PTC2E-1AD
BTW, while looking into working with Sigrok, I noticed in the fluke-dmm driver source code that there is provision for 9600 baud and 115,200 baud. The Fluke 187 would not respond at the higher speed, but then the 'spoon test' - reflecting the transmitted signal back to the receiver - also failed at this speed. The LED I have used has a rise/fall time of 800nS, whereas it is possible to get IR LEDs that have a much shorter 15nS rise/fall time. It seems therefore that the IR LED I have used is a bit slow for 115,200baud, although still perfectly adequate at 9600 baud. The receiver seems to react in time intervals measured in uS so not a problem. The other question however is, whether the Fluke 187 IR is capable of transmitting at 115,200 baud? I see no provision to change the transmission speed in the setup and no mention of it in the manual, so am presuming it is fixed at 9600 baud, but I stand to be corrected.
UPDATE: The Fluke Remote Interface Specification document states that for the 187/189 the speed should be set to 9600.
http://www.pewa.de/DATENBLATT/DBL_FL_FL187-9-89IV_BEFEHLSSATZ_ENGLISCH.PDF (http://www.pewa.de/DATENBLATT/DBL_FL_FL187-9-89IV_BEFEHLSSATZ_ENGLISCH.PDF)
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I added some indicator LEDs and finally got around to actual contruction.
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Connected to the PC and working with Sigrok. I have attached my notes with more technical detail as well has how to connect and get it working with Sigrok.
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Very nicely done. When I have the time I'll make one for my 187 :-+
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an ebay link : https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884? (https://www.ebay.com/itm/USB-optoisolated-IR-adapter-for-Fluke/182450421884?) for 22$ usd free shipping ????
To be honestly, now it slightly expencive.
Post charges become is about $6 USD from beginnig this year. :(
I also thought for provide it with case for 280 series metter, but it requred over $ 5000 initial investment for plastics molding and 100-200 cases included in this price. And I not sure for chinese quality.
I provide STL files for case developed for 280 series metter, so customer can print it oneself if they have access to LCD/DLP/SLA 3D printers. But this files is compartible to the v.1.6.4. board (white PCB)
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Trying to make thisone https://www.youtube.com/watch?v=k6FPeUcDfpc (https://www.youtube.com/watch?v=k6FPeUcDfpc)
But also seem to struggle with IR leds .. tryed a bunch of them don't seem to get any data .
https://www.thingiverse.com/thing:3404723/files (https://www.thingiverse.com/thing:3404723/files)
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Make sure you're not using a photodiode in place of a phototransistor.
The other common problem is matching the optoelectronics wavelengths for best sensitivity.
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I have quickly made the schematic of WaveyDipole .
Works perfect on CH340 Usb to TTL and CP2102 .
Instead of the usb to serial i hooked rx & tx and gnd to ESP module ( 8266 ) and wemos variant .
It seem the ESP is sending out the ID command and the fluke reponds ( checked on scope with serial decode ) and also sniffed with usb to serial on the ESP ..
So the problem seems to be the data doesn't get decoded on the esp on the RX side .. so no values or published to webserver .
i sued following diode & foto transistor . ( working pefect using USB to serial following WaveyDipole schematic )
TSAL6400 INFRARED EMITTER 940NM T-1 3/4
L-53P3C PHOTOTRANSISTOR, 5MM, 940NM