T&L Publications

I need to isolate a motor driver from the parellel port on my computor. I want to use a optoisolator but don't know how they work. Can anyone help? The ones I have seen are six pin packs, transistor and Darlington output NPN. A link with good info would also be great if available. Basic circuit disign and such.<p>Thanks for any help you can lend.<p>Bob

An opto isolator is an led and detector.
There is no electron flow between them. A voltage turns on the led, which turns on the detertor which turns on the voltage on the other side.

The six pin opto isolators usually have the LED connected anode to pin 1 & cathode to pin 2. The transistor connections depend on the type, you need the data sheet. Go to www.mouser.com or [url=http://www.digikey.com,]www.digikey.com,[/url] put in your part number and search for the data sheet (at digikey, keep clicking on the part number). The claire device is $0.62 at digikey, part number LDA110.

So then am I correct to think there are three leads, emiter, base and colector that are in a on or off state only? Or does the voltage at the gate vary the amount of current threw it? <p>Bob

In most cases you would leave the base open, altho if the temperature was high and leakage was turning it on, a high value resistor from base to emitter would be called for.

A good place to start lookin for designs is for MIDI ports. They use the opto and will give you all of the relevant values to make these isolators work with a computer.

If you're a "newbie", and want a "KISS" circuit to optoisolate logic 1s and 0s, try the H11L1. It has everything built in except the current-limiting resistors for the LED at the input and the pullup for the open collector logic gate at the output. Also, it's made with hysteresis (no in-between voltages -- it's either on or off, 1 or 0), and it will turn on with 1.5mA of LED current, which means you can drive the LED direct from your parallel port without worrying about smoke. The only problem is you pay about 3 or 4 times as much as a 4N29 or 4N35. Here's the data sheet on the opto...<p>H11L1 .pdf datasheet<p>Looking at the application circuit on page 4, use a 1.5K series resistor on the LED side (that'll give you 2mA of LED current), and drive the LED by connecting the PRN pin to pin 2 instead of pin 1, and tying pin 1 to +5V. That will allow a logic 1 at the input to cause a logic 1 at the output, and also make your PRN pin sink current instead of source, which might be helpful. The output at pin 4 is open collector, which means you'll need to choose a resistor which will draw about 5mA when the output is low (1K is about right if you're using 5V on that side, too). Also, your output voltage can't exceed 15V. <p>For information on using the PC serial, parallel and USB ports, check out Jan Axelson's Lakeview Research web site, and look at her book "Parallel Port Complete". It has all the answers you need, and also has programming examples in BASIC and C.<p>Lakeview Research<p>Happy hunting.<p>[ July 29, 2003: Message edited by: Chris Foley ]</p>

Thank you for all the help!!<p>I am very much a newbie. I think I will go with the H11L1. I think the best place to get it would be Digi-key? Any other coments or sugestions, I'm all ears! I can't wait to make something that is sortive complicated and works!<p>Thanks again<p>Bob

check out electronic relays, They are the same thing designed to transfer power.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by toejam:
check out electronic relays, They are the same thing designed to transfer power.<hr></blockquote><p>If you're thinking of SSRs as electronic relays, then you have to bear in mind that they are a LED and an opto triac in most cases.<p>colin