Hi
This optocoupler is not switching my 2k ohms pull up to ground!!
Simple circuit using a ILQ74 Optocoupler --> https://www.vishay.com/docs/83640/ild74.pdf
aqibi2000:
This optocoupler is not switching my 2k ohms pull up to ground!!
Most people here aren't clairvoyant. You need to describe or explain what measurements you got. And explain what you mean by 'not switching your 2 kilo-Ohm pull-up to ground'. Explain where you're measuring the voltage differences etc, and explain what values of voltage difference you're getting.
There's a photo-transistor on the output. When the transistor in a saturation state, the terminal voltage at the lower-voltage side of your 2k resistor might be say 0.3 V, or somewhere around there.
What you could do is .... put a multi-meter in series with your 2k resistor..... and measure the DC current, just to see what value of current you're getting for the collector current. It it's too low, then you might have to 'up' the diode current.
Also, you could use the multi-meter to measure the current through the 220 ohm resistor as well. Just to make sure the measurements are ok.
There is always a reason that something doesn't work.
If you have replaced the optocoupler four times with the same null result, then the problem is very clearly not the optocoupler, but operator error.
Wrong part, wrong power supply, wrong polarity, wrong wiring, bad connections.
Can you show us a photograph of your layout? or at least indicate pin numbers on your schematic.
You have drawn a generic schematic of a circuit that should work.
However non of the four opto-isolators in that package have their pins arranged in that order.
My guess is that when you tried one quarter of the package, that you had either the LED or phototransistor the wrong way round, and that when you went to the next quarter (where both parts are flipped), that you corrected one mistake but introduced another.
We know your wiring is okay.
Show us a good image of your wiring.
Your CTR is ~35% so you should be able to get ~5ma max. @Rc ~1K.
What is your load going to be?
aqibi2000:
The output of the Opto is switching from VCC to 0.08V.
What is wrong with that?
Go to the data sheet and look up the saturation voltage of the photo transistor, it is normally called Vsat.
Yes their is always a resign why something does not work. If their was not then we would not have laws of physics, which always apply, except when beginners are in a lab when they exhibit a sense of humour.
Provide a separate 5V supply for the output (common ground) and try again
Hi,
Please post a picture of your project?
Thanks.. Tom.. 
Hi,
The output of the Opto is switching from VCC to 0.08V.
There should be no issue in the photo-transistor sinking 2.5mA to ground entirely (being my issue).
So when you have the diode not conducting current, you have 5V, Vcc on the Vout of the opto.
When you have the diode conducting you have 0.08V on the Vout.
Because you are using a BJT as the output device there will never be a direct short, 0 Ohms, Emitter to Collector.
Whats the problem?
Tom...
aqibi2000:
The sole purpose of using the optocoupler was to isolate the noise motor controller from the Arduino.
You are using the same supply for the input and output according to your drawing. It is not isolated hence why I said use a separate PS for the output
aqibi2000:
with regards to the saturation surely if being driven to just sink a current 50% below it's absolute maximum rating the output should be 0v.
The datasheet states a typical transistor saturation voltage of 0.3volt with 2mA collector current and 16mA LED current.
If you want/need lower than that, swap the 2k resistor and the opto transistor.
Then that saturation voltage is taken off the 5volt supply.
I just saw that that 2k resistor is part of the motor driver.
And yes, powering the LED from the same supply as the opto transistor defeats the use of an opto coupler.
Leo..
with regards to the saturation surely if being driven to just sink a current 50% below it's absolute maximum rating the output should be 0v.
No it should not, and will not, be.
You seem to have an attitude problem here coupled with an incomplete knowledge of electronics.
Also you post a circuit containing no motors and then suddenly start talking about a motor.
Also if you use the same 5V line and ground as the Arduino then the opto isolator can not be expected to reduce any noise generated by the motor.
It's not isnking the 2.5mA to enable the motor
OK let’s get this straight if you are reading an output voltage of 0.08V from that transistor the opto isolator is working.
Any further circuits need a schematic not an explanation because we have already established you don’t know much about electronics. I assume you are not driving the motor directly from the opto so you must have something in between. We would like to see what. I assume you are also using a back EMF diode.
aqibi2000:
I have a Degree in Electronic Engineering and was therefore asking specific questions, and the blunder was expecting the NPN to saturate 2.5mA to ground.
Why do you need it to saturate to gnd?
Tom..
I have a Degree in Electronic Engineering and was therefore asking specific questions, and the blunder was expecting the NPN to saturate 2.5mA to ground.
In short, operator error.
In this particular case, failure to read and understand the device specifications, which, in the future, I will add to the list in reply #2.
aqibi2000:
That won't be till after work, but I can assure you it's electrically connected correctly. Gosh why so much doubt with people if I stated the otpocoupler is performing a switching motion.with regards to the saturation surely if being driven to just sink a current 50% below it's absolute maximum rating the output should be 0v.
wawa already pointed this out already.
The photo-transistor is going to provide a "Vce" (voltage across collector and emitter) of around (typically) 0.3 volt when the photo-transistor is operating in a saturated condition (with your particular applied diode current of 15 mA). Vce won't get down to anywhere near 0 volt (like 0.000001 volt etc.), because we're dealing with a bipolar junction type of transistor here.
Whatever you're measuring for Vce, you should get something like this.......as follows. If the transistor is cut-off, then Vce should come up to maybe around 5 volt. And once you apply the appropriate amount of current to the diode to get the transistor into a saturated condition, you should get Vce of around 0.3 volt (or so).
In your case, you reckon you're getting 0.08 volt, which doesn't sound right for the particular amount of diode current being supplied (eg. 15 mA). But then again, as long as it is really switching ..... then well...... at least it's switching.
This diagram you drew is what we're all (in this thread) assuming you have connected up --- only.
But..... once again, what you got to do is to take your multimeter and do some measurements. Go ahead and show us some electronics techniques being applied. Measure the diode current (DC current). Then measure the current through the 2k resistor. Also measure Vce and the voltage across the 220 ohm resistor. Then change the 220 ohm resistor to some other value....eg 270 ohm, and repeat those same measurements above (ie. diode current, and the current through the 2k resistor, and Vce and the voltage across the 270 ohm resistor).
Also, with no current flowing through the diode, measure Vce.
aqibi2000:
The motor does not switch on unless I physically short the pins of the collector and emitter (so I'm assuming it's got to be the issue with the opto not fully pulling the voltage to ground) - only logically step I could foresee.
- What is the specification of the motor controller, part number, link to spec sheet.
- Show us a circuit diagram of how you connect the arduino to the opto to the motor controller.
- Draw you circuit on a piece of paper and photograph it please.
- Please post a picture of your complete assembly.
Thanks.. Tom..
Hi,
So you have an AMC 2500 Controller with 2 x GS D200s Stepper motor drivers on board.
This controller is driven by a comms cable, so how are you connecting the the GS D200s?
If you are jumping into the D200 and haven't disconnected any of the controller circuitry that may be still connected to the D200 input pins, then your signal could be going all over the place, a dead short to gnd looks like the only way to get a signal into the D200.
I would say if you managed to disconnect any tracks to the input step pin of the D200 on the PCB you should be able to control it with an opto.
But if you desire opto-coupling without modifying the PCB, then get the opto to switch the NPN transistor.
Tom....