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paralel port opto-insulation

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bogdanfirst

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i want to attach some devices to the paralele port. basically i need to insulate the computer from the rest of the things i'l' control.
so i need some opto-couplers, preferrably logic to logic ones. if more than one is integrated in one pachage then it is best. i need to insulate the 8 bits.
i can't find a schematic better than some simple opto couplers and a transistor as amplifier. but i need to use 8 like this.
i searched the net but i couldn't find anything usefull. it would be best if the parts are easily available and also cheap.
can anyone help?
pls....
thanks in advance
 

bogdanfirst

New Member
thanks. but this is not what i wanted.
this is just a smiple interface, that connects the relays, one to each bit.
what i want is to connect a more complex circuit, wich i will control much more things. so i want to insulate 2 digital devices, the computer and the circuit and i don't want them to have the same ground.
so i need to insulate the 2 devices.
any ideas?
 

bogdanfirst

New Member
well, i don't know how the prices are there, but here they cost more than 2 euros one. i don't think that this is a good solution.
so is there a solution so that i can use simple optocouplers(the ones with transistor output) and interface them with some 74HCxxx IC's?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
bogdanfirst said:
well, i don't know how the prices are there, but here they cost more than 2 euros one. i don't think that this is a good solution.
so is there a solution so that i can use simple optocouplers(the ones with transistor output) and interface them with some 74HCxxx IC's?

You should be able to feed a TTL chip from a standard opto-coupler with a simple pull-up resistor, you certainly could a CMOS logic chip.
 

Sebi

Active Member
Exo: not BC, PC...
Bogdan, the PC817 very poor and slow for data transfer. The logic optocouplers contains also a schmitt-trigger.
Once i've tried isolate the AD conv. from micro. but always freezed.
I've changed to TLP115 and work without problem.
Try 6N136 (0,2us), 6N137 (0.06us).
Maybe 6N138 ( (H to L=10us,L to H=35us), 6N139 (H-L=1us,L-H=7us)
us mean microsec
 

bogdanfirst

New Member
i think that i'll go for the 6n137 or 136. i'll see wich one is available.
but, i got one more question.
for the inputs, does the port have pull-up resistors inside?
if not, how can i insulate the inputs without the need of +5V from the computer?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
bogdanfirst said:
i think that i'll go for the 6n137 or 136. i'll see wich one is available.
but, i got one more question.
for the inputs, does the port have pull-up resistors inside?
if not, how can i insulate the inputs without the need of +5V from the computer?

You generally need 5V at the computer side!.
 

bogdanfirst

New Member
i decided on 6n137. i have already ordered them. 2 bad the outputs are inverted.
i'll also add an inverter. i'll post the schmatic and the PCB when i finish it.
thanks for the help.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
bogdanfirst said:
i decided on 6n137. i have already ordered them. 2 bad the outputs are inverted.
i'll also add an inverter. i'll post the schmatic and the PCB when i finish it.
thanks for the help.

There's no need to invert them in hardware, simply do it in the PC software! - that's the advantage of using software!.
 

bogdanfirst

New Member
yes, i have thought of that. but i also thought that i might use this interface for some other applications, where i will not be able to invert them.
by the way, do you know any octal buffer wich i can set it to be inverting or non inverting? this way i could also select by hardware if i need to invert it or not.
i think i will post the circuit at the projects section after i complete it. some other people might need it.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
bogdanfirst said:
yes, i have thought of that. but i also thought that i might use this interface for some other applications, where i will not be able to invert them.
by the way, do you know any octal buffer wich i can set it to be inverting or non inverting? this way i could also select by hardware if i need to invert it or not.
i think i will post the circuit at the projects section after i complete it. some other people might need it.

You can use an XOR gate to invert or not, by setting the other input either high or low.
 

bogdanfirst

New Member
that's a good idea....though i will have to use 8 gates. i think that the circuit will be more complicated. but it is worth to do it like this.
i think that i will use 2 74HC86 ic's. this seems the best solution.
 
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