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Need help with making a Fluke optical usb link.

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This is my first post on here and apologies up front as this is a "where do I go next" plea.
My background is more HT electrics than electronics and although I learnt about electronics at uni, it is far too long ago than I care to remember, but I still recall much of the basics.
I am trying to make an optical to USB lead for my FLUKE 123 and have found a board that does most of the hard work for me in taking the TX and RX optical pulses and converts them to USB DATA so FlukeVeiw software can read it.
I have purchased the following Infra-red LED and Photo transistor to couple to the scope.
The schematic looks like this( link is eagle format only)
I have substituted the LED load resistor to a 47 ohm to suit the 3.3Vdd, 1.6Vd, 40mA. requirements of the LED from my local supplier.
Unfortunately it dont work!
After a few trials and tribulations I have managed to get the photo-transistor to conduct only when there is a constant light source. The intermittent data pulses from Flukeview (verified by substituting a Green LED for the IR) don't seem to switch the Photo-transistor fully!
At this point I'm stumped.
Is the Photo-transistor to slow to acknowledge the pulses from the IR diode or are the pulses not intense enough?
What else should I try (Buy a Fluke lead at £100 and be done with it I hear you cry) :'(

It is a good idea to post schematics as a JPG rather then schematic files.


Uploaded with ImageShack.us

Hope the link worked ;)

It is likely the transistor does not have enough gain to switch without amplification.

Here is what you do.

Set up an IF LED with a resistor of about 3k3 and a switch to a 5-6 volts supply so you can turn it on and off.  Put the transistor in about the same orientation as it is to the fluke diode.

You will probably have to keep the light away from the LED/Transistor pair. The transistor probably responds to visible light and that will swamp out the effects of the IR light.

Connect the transistor up to 5V but add your multimeter on current range in series with the 1K resistor. So the multimeter is reading the collector current.

See what happens with the collector current as you turn the LED on and off.  Once you have these figures, you can probably work out what you need to do to make it work.



The Scopemeter interface uses a 875 nm IRED as a transmitter. As a receiver the 950nm device works OK. If you do not know your LED and it looks broken (both wavelengths cannot be seen by the human eye) check it with a digital camera or the camera in your phone. A bright white color is a 875nm. A purple haze is a 950nm.
Here ar some pictures taken with a HP307 Photosmart camera

 This is the 875 nm

this is the 950


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