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Topic: Connecting an Oscilloscope to Opto-coupler? (Read 3414 times) previous topic - next topic

naut

greets

I want to connect the oscilloscope to an opto-coupler (6N135) to monitor serial messages from an Attiny2313a. I have a sketch that sends different variables (bytes, integers) to the TX port using Serial.write command at different baud rates.

I've used this schematic from here http://www.instructables.com/id/Send-and-Receive-MIDI-with-Arduino/?ALLSTEPS:



Instead of the Arduino I have the oscilloscope, and the input (midi socket) is coming from the Attiny. I've used this midi circuit because later I want to use oscilloscope to display midi messages.

So I have a few questions:

1) I connected the

Attiny 5V pin to 6N135 pin 2

and the

Attiny TX pin to 6N135 pin 3.
Is this the correct?

(I've replaced the diode between pins 2,3 with a LED).

2) I don't know how to connect the scope, since it only has the probe and the ground connector. The opto-coupler has 3 connections, 5V, Data, and ground. How do I connect them? I've tried different combinations, but I either get a steady 4.5 volt line (I use three 1.5V batts to power the 6N135) or no reading at all.

So for now the only way I can monitor the data from Attiny is if I connect the scope directly, i.e. the probe to the TX pin and the ground connector to the ground pin on the chip.

I would appreciate any help on this, thanks

semicolo

Why do you want an optocoupler between the Attiny and the oscilloscope?
You need to power the optocoupler, if you use the Attiny +5V, you defeat the optocoupler's purpose.
You could use another +5V power supply, connect it's +5V/gnd in place of the arduino, connect the oscilloscope ground to the same ground (pin 5) and the probe to pin 6

Boardburner2

That instructible is designed for the midi interface which has a current sink and current source on 4 and 5 or vice versa.
The opto needs 20 ma which midi can supply I think, just connecting it to a microprocessor will not necessaarily work, what current can the actiny supply and sink in its data pin ?

naut

Quote
Why do you want an optocoupler between the Attiny and the oscilloscope?


Well, I want to use opto-coupler later for inputting midi to the Arduino just like on the schematic.

Quote
You could use another +5V power supply, connect it's +5V/gnd in place of the arduino, connect the oscilloscope ground to the same ground (pin 5) and the probe to pin 6


I've tried this with two 6n135's and the scope still does not read anything.

hmm....

naut


The opto needs 20 ma which midi can supply I think, just connecting it to a microprocessor will not necessaarily work, what current can the actiny supply and sink in its data pin ?


I wish I knew how to find this info in the datasheet

I connected a led instead of the 220ohm resistor R3, the one attached to pin 2. When the Attiny sends data the led blinks.

I also tried connecting a led between pin 8 and pin 6, it blinks at the same time as the other led does, so I guess in a way it works, except the scope does not show anything.


Boardburner2

The led blinks !
You have the polarity wrong.
Midi spec is 5 ma for a logic 0
0 ma for a logic 1
Current only flows for a logic 0
If the circuit was working correctly the led as connected in yor diagram should not work at all.

naut

Ye I know, but that's not the led I was talking about, it does not blink. I only replaced the 220ohm resistor with another led, just to see if there is continuity, that is the led that blinks, not the one drawn between pin 2 and 3.


Anywho... I removed the 10k resistor R1 and the circuit works! Maybe there is a big difference between the 6n135 and the 6n138, and the 10k resistor between pins 5 and 7 was messing the whole thing up.

Boardburner2


The led blinks !
You have the polarity wrong.
Midi spec is 5 ma for a logic 0
0 ma for a logic 1
Current only flows for a logic 0
If the circuit was working correctly the led as connected in yor diagram should not work at all.


Edit
Apologies for the earlier post, I was thinking of something a bit different, late 80s / early 90 s i think I had a lot of grief with midi interfaces in the real world.

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