Re: [CAD_CAM_EDM_DRO] TTL to HTL signal conversion

Lars Levin wrote:

>Hello Group!
>
>I have a couple of old servodrives with step/direction
>inputs, but they use HTL signals, logic high is 24v
>instead of 5v.
>I want to be able to connect these to the parallell port,
>and therefor need some converter.
>Is there anybody that have some schematics or ideas for
>a preferably opto isolated 5v to 24v and 24v to 5v converter.
>
>

Assuming the speed is moderate, you can build this pretty easily.
The parallel port doesn't have enough current capability to operate
many opto-couplers properly. But, if you use an external source
of +5 V, such as a hard drive connector or pin 1 of the game port,
through the LED on the opto-coupler, a series resistor and then to the
parallel port output pin, you get the highest current drive.

Digi-Key has the H11A817D which should be suitable for this purpose.
The wiring would be as follows :
Pin 1 goes to +5 V.
Pin 2 goes to one end of 510 Ohm resistor.
other end of resistor goes to parallel port output pin.

And for the output :
Pin 4 goes to the HTL imput.
Pin 3 goes to the ground of the driver.
If the driver needs a pull-up to 24 V, you'd need an appropriate resistor
from +24 V to pin 4. Something like 5 to 10 K Ohms would be a good
guess.

The polarity will be as follows :

When the parallel port pin is at 0 volts, the LED will light, and the
HTL signal will go to 0 volts.

Jon