Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Parallel port break out board for CNC

Not open for further replies.


Advanced Member level 4
Dec 2, 2010
Reaction score
Trophy points
Activity points
I am planning to buld a CNC (just for fun). I bought the stepper and driver and am playing with it (thanks to edaboard forum guys).
I need a break out board DB25, which is available on (comparatively cheap - $5). The issue is - it will take around 25-30 days to reach me (it always did when bought on ebay). I am trying to buy one because - before I tried to build few DB25 based PIC programmers and it all failed, finally bought a PICKIT from ebay. Presently I am working on a laptop and have heard if I use any USB - Parallel converter , it will not work well. I still have the Desktop pc with all ports that I will be using (It had winxp back then). I simply doubt if the port is working. I have seen lot of Parallel port programming all over internet (mainly the led blinking and all). I thought it is better to test it or check it using the leds....

I searched forums and articles and found few DB25 breakout boards, 90% without a direct connection to the outside world (may be protecting the pc from any voltage getting in, from the connected device.) majority of them have 74xx245 as tristate buffer, or optocouplers. The 8 datapins I think it connected to pulse pin and direction pin of the steppers.

correct the following if wrong plz
1. Though bidirectional communication is possible all CNC connections are unidirectional.

2. so can connect and protect all connections with an optocoupler instead of an IC

3. In a listing in ebay they say have used 6N137 on breakout board (saying the fastest) and can provide fast response.
using PC817 instead of 6n137 matters?

4. 8 data pins are connected to control pulses and direction of stepper and drill or cnc motor.
5. control and status pins are for limit switches etc, which can be hushed for testing purpose.

6. There are inverted outputs , which require an inverter IC to properly interpret.

I checked this post
it says about using 74AHCT245 but not 74LS245s. What is the issue , it really matters?

I have searched the forum and found few links to real breakout board design.
but I am doubtful about the usage of 74x245 or octocoupler. Because all designs use this items differently. one use octo. other use 74x245 , another use 74x00, some with both octo and IC., etc. if we are using it for CNC response and speed does matter?

Not open for further replies.

Part and Inventory Search

Welcome to