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Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
This is thread is somewhat connected to the universal DRSSTC Drive 2.5 thread, but I didn't want to muddy the waters. I have been having trouble with various FO receivers, and so ordered the PF2414T receiver and i just completed the circuit as illustrated in the UD V2.5.
Here is what is happening:
When I connect the O-Scope to the output, no input light signal, and I turn on the power, the output jumps HI. If I apply a signal, it starts responding perfectly. It's like it needs that first signal to establish a normal operating state, else it can randomly go HI or LO (mostly goes HI). I can't risk forgetting to send a signal when turn on and have the coil go CW on me. I have been through 3 different types of receivers and I get the same response with each one.
It must be something I am doing wrong, as everyone seems to use these OPF receivers without issue. Any ideas what it can be?
I've never used that exact receiver bu I had similar issues with a FB-129 receiver. I had to remove the biasing resistor shown between Vcc and Out in order to achieve stable operation.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Hmm, that's very odd it goes hi indefinitely. How hi does it how's on your oscilloscope? I assume it would be no more than 5ish volts. Since you tried all the different fiber optic types, this might point to a problem elsewhere on the board perhaps.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Keep in mind that the HFBR-2412T and the OPF2412T are both open-collector devices, you need that resistor in the circuit to establish a high state when the unit is not active. Without that resistor your output will be in an undefined state. When a fiber optic signal is received the output transistor is turned on pulling the output low. These units are active-low output.
I have never personally had the problem you are describing when using these RX units, so it may be something with your setup. Lets start with you fiber, you should be using ST-ST multimode fiber (I usually use 52.5/125) The datasheet sheet specs are variate of sizes that work with the receiver. Just because it's ST fiber and plugs into the unit doesn't mean it will work properly.
Also what unit are you using for TX? It should be a HFBR or OPF1412T or similar variant with a 100 ohm or so current limiting resistor (if driven from a 5V rail).
When you first power up the unit, the output should be high, and stay high until a signal comes in and activates the RX unit and pulls the output low.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I am using the OFP1412T for TX. The cable is a 62.5/125 ST-ST (mouser part# 571-5349573-5).
I checked the resistor again as this seems to be the problem - found a solder break, so I don't think it was pulling up. Now without a signal the output stays LO - Hooraah! Redoing the TX circuit later today to make sure everything is working ok.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I just rebuilt the TX circuit quickly before heading out - everything working perfectly. Now to connect it all back and run the coil. Thanks again - helps talking through these things sometimes
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Fiber Optic Receiver
