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/projects/fluke-187-ir-cable/msg956662/#msg956662Also this site here:
http://kimboricha.blogspot.co.uk/2013/12/build-usb-to-fluke-189-irinfrared.htmlIt 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.