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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
 
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?
 
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?
 
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.
 
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
 
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?
 
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!.
 
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.
 
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!.
 
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.
 
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.
 
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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