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Neen secound hand opinion on circuit diagram for PC-mod

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jrolands

New Member
I'm building an extreamly cool mod for my computer and i just want an secound hand opinion on the circuit diagram i made:
**broken link removed**

D(x) in the circuit is one of pin 2-9 on the parallel port, R1 and R2 are ¼W resistors on 68ohm, and LED1 and LED2 are 3.6V on 20mA.
I know there is something missing here, i just can't determen what..
Please reply
 

Exo

Active Member
First of all you need a resistor between the parallel port and the optocoupler's input pin 1. Because parallel port levels are at 5V and the LED inside the optocvoupler VF = 1.5V.

Also consider not all parallel ports can deliver enough current to light the led inside the optocoupler. I've seen parallel ports wich could not deliver more then 5mA in wich case you would need to buffer the port. But if you buffer the port with a transistor for example then you lose optical seperation and the entire concept of using a opto is just to do that.

Secondly, the detector transistor inside the opto is a NPN. Wich means you cannot switch the positive side of your 5V source with it. You should switch the negative side. So connect the leds to the 5V power supply + and the - trough the opto.
 

hantto

Member
Hello! :)

I also tried discolitez, and with the same optocoupler, but just with one led. I had a 1kohm resistor in series with the optocoupler's led, and a led with a resistor at the optocouplers transistor. And it worked fine and dandy :)

P.S I't was quite fun to look at those super bright leds falshing :)
 

Exo

Active Member
Almost right, You just need to swap pins 4 and 5 (4 = emitter, should be connected to -, 5 = collector to leds)

As for the resistor, according to hantto 1K worked, so give it a try
 

jrolands

New Member
now take a look at this. this is the whole thing.. it's actualy for displaying a sound graph, pretty sweet hu? ;)
**broken link removed**

Now keep in mind that i'm a newbie so i'm not that sharp when it comes to stuff like this..
 

panic mode

Well-Known Member
I would use optocouplers with high gain in digital applications.
 

ljcox

Well-Known Member
Need second opinion on circuit diagram for PC-mod

jrolands said:
okey.. one more thing i was wondering about..
the shop where i'm bying all this components from has the CNY17 in 2 versons.. and i don't know wich one to pick..
CNY17F-1 or CNY17F-3
take a look at it here

My knowledge of Norweign is zero, so I assume that "Kopplingsfaktor" means coupling factor.

So I would use the CNY17F-3 as it has a higher Kopplingsfaktor.

Len
 
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