Hey, guys

I been reading the posts about controlling a motor using a Parellel and serial port (since I want to do the same) and was wondering if it was possible to do without all those microcontrollers and PICs. You see, the Parellel port can carry a load upto 5V and 2.5mA. Now the problem is the Amperes. Most normal motors can work from 1.5V onwards (exept the 12V ones). But the minimum load on a motor is atleast 1Amps. So the miserable 2.5mA generated by the serial and parelle ports is not enough.
:cry: But we can get around this by 2 methods.
1) By using an optoisolator. This is better because there is NO COMMON GROUND and also the optpisolator also isolates the current of one circuit from another.

2)By using a Current or Gain amplifier.
since the input is 2.5mA and we need 1A on the other end the gain would be 400. So if we can build an amplifier with a gain of 400 our problem would be solved. Since we will be using common ground here the output comes from any of the 8 data pins of the parellel port and goes to the current amplifier from which the output goes to to the motor.
Oh, and by the way we can also use a normal relay to change the direction of the motor if we dont want to use a H-bridge.
Now does anybody out there know how to build a current amplifier with a gain of 400??? :? :!:

 

Sorry to state the bleeding obvious, but isn't a bipolar transistor, generally speaking, a current amplifier?? :wink: eg TIP111: gain = 750

 

Use darlington transistors for large current gains.

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Hey come on guys,
I thought that you would gimme a circuit
But anyway, Ive resorted to using an optocoupler. :lol:

 

http://www.hut.fi/Misc/Electronics/c...el_output.html

scroll down you'll see the opto/darlington driver i use and it works perfectly if your clever you can make it on stripboard very compact
the 5 pins on the 9way d plug line up nice with the strips for soldering on

and just for thought i have used this setup with highside drivers from ebay £1.99 for 10 IPS511 thay can handle 5A each

( im clever i just get strip board cheep :wink: )

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