what resistor for a 4N35 opto

Hello all

New to using optocouplers, so I would like to know what resistors to use

I will be putting 12V very low amps across pin 1 & 2 (+12V pin 1 ov pin2) WHAT resistor value do I need between +12v and Pin 1??

I want to switch 12V at higher amperage, di I use pin 6 & 4 or 5 & 4?? do I need a resistor if so what value?

Thank you for replies in advance
Tim

Datasheet here.

Current transfer ratio is only 40%, so 10mA in only gets 4mA out.

What are you trying to drive with the output?

Where is the input signal coming from?

Trying to drive a relay to get closed & open signal to a gps.

The input 12v is from an agricultural machine but is of too low a power for a relay.

TimFR said:

Trying to drive a relay to get closed & open signal to a gps.

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I would really be surprised if the GPS input requires a relay. More likely, it wants isolation that a relay might provide. If you are using an opto-isolator, you may be able to interface your opto-isolator output directly to the GPS input, in which case your problem becomes more about driving the input of the opto-isolator.

What specs can you find about the GPS inputs? Voltage levels? TTL? CMOS?

TimFR said:

The input 12v is from an agricultural machine but is of too low a power for a relay.

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Is there a spec on the output suggesting it comes from a CMOS output, or is it from a sensor that has an open-collector, open-drain, pull-down only type of output? If might say something like "sink current=Xma"? Possibly "source current= YmA"?

MikeMl said:

I would really be surprised if the GPS input requires a relay. More likely, it wants isolation that a relay might provide. If you are using an opto-isolator, you may be able to interface your opto-isolator output directly to the GPS input, in which case your problem becomes more about driving the input of the opto-isolator.

What specs can you find about the GPS inputs? Voltage levels? TTL? CMOS?



Is there a spec on the output suggesting it comes from a CMOS output, or is it from a sensor that has an open-collector, open-drain, pull-down only type of output? If might say something like "sink current=Xma"? Possibly "source current= YmA"?

Click to expand...

I was going to use a relay to invert the reading as when the GPS expects it to off it is ineffective on and vice versa.

I don't know where the output comes from, all I Know is it is too low powered for a relay.

Relay is a poor way to invert the signal. If you were going to use a relay, why do you also need an opto-isolator. Do you need to isolate at all, or just invert the logic?

Lets see if you can answer this: If the signal out of the farm equipment is high (a few volts positive measured with respect to some ground wire in the farm equipment, do you want the GPS input to be pulled low?

You own a multimeter? If so, go make some basic measurements to answer the questions posed above and in the attached diagram.

MikeMl said:

Relay is a poor way to invert the signal. If you were going to use a relay, why do you also need an opto-isolator. Do you need to isolate at all, or just invert the logic?

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An opto-isolator because the signal is too weak to power a relay

MikeMl said:

Lets see if you can answer this: If the signal out of the farm equipment is high (a few volts positive measured with respect to some ground wire in the farm equipment, do you want the GPS input to be pulled low?

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Yes

[/QUOTE]You own a multimeter? If so, go make some basic measurements to answer the questions posed above and in the attached diagram.[/QUOTE]
The machinery diagram is spot on
When high it has got voltage & low no voltage (12v)
V1 is 12V

Can you explain how to measure the amplitude when not attached to a load (sorry if I sound a bit thick !)

Thank You

Hi Tim,

Sorry, I got busy, and haven't replied.

First, do you have a manual on the GPS? If it is like the one in my brother-inlaw's big tractor, then it came with a manual that is about 500 pages long...

In it there will be a section on interfacing sensors to it. It should tell you what it expects as an input high logic level, usually >3V, but it may have a "not to exceed" voltage level. It may also say something like "relay input" or "active pull down".

It will also answer the question as to if "optical isolation" or "relay isolation" is really required.

If "isolation" is not a requirement, but a logic inversion between your sensor and the GPS is required, then a simple switching transistor used as an inverter will do the job. We still need to know if the inverter requires a "pull-up" resistor, or not. If it does, we also need to know what supply voltage the top of the pull-up resistor must be connected to? If the GPS needs the external logic to drive a positive current into the input to get a logic high, then it might output that supply voltage on another pin in the interface connector. That would be listed in the manual, too.

Can you scan an post the interface connector and specs on here?

Hi Mike

Thanks for your reply.
My GPS is Trimble and all I have is the User manual however I put together a circuit based on your diagram. I played around with resistors and ended up with a 220 ohm on anode pin 1

I have tested the circuit and it works fine.

Thank you very much for your help. Could you recommend an on-line or pdf based self learning electronics as I find it really interesting and would love to learn more.

Tim

Did you use both the opto and the transistor, or just the transistor?

As for an online-tutorial, . I just wish they didn't confuse the reader with their anachronistic "electron current flow".

MikeMl said:

Did you use both the opto and the transistor, or just the transistor?

As for an online-tutorial, . I just wish they didn't confuse the reader with their anachronistic "electron current flow".

Click to expand...

I used both.

Thanks Mike