Comments on: LogoChip and PWM: Bidirectional Motor Speed Control

By: Keith Neufeld

Keith Neufeld — Wed, 04 Mar 2009 17:16:25 +0000

Ernesto, excellent work!

By: Ernesto

Ernesto — Wed, 04 Mar 2009 17:13:06 +0000

Thanks Keith… I now reproduced the circuit using 4 NORs.

By: Keith Neufeld

Keith Neufeld — Wed, 04 Mar 2009 15:59:28 +0000

Ernesto, an AND is equivalent to a NOR with both of its inputs inverted.

Redraw the diagram, replacing the AND with a NOR. Then on each input, use a NOR gate with one input tied to ground as an inverter, and start tracing logic signals through it, and I believe you’ll be able to figure it out quite quickly.

By: Keith Neufeld

Keith Neufeld — Wed, 04 Mar 2009 15:57:54 +0000

Ernesto responded:

I’ve tryied to reproduce the AND with NOR GATES but now I’m not very good at
De Morgan Laws. The final circuit would be using only a quad NOR gate to
control de PWM into the HBridge?

By: Keith Neufeld

Keith Neufeld — Wed, 25 Feb 2009 16:57:27 +0000

Ernesto, I do remember having looked at Mike’s file, although it was over a year ago and I don’t remember much detail. But it’s easy to recreate.

Look at my drawing with one inverter and two AND gates. Then remember that a NOR with one active input and one input tied to ground acts as an inverter, and apply De Morgan to replace the AND gates with NOR gates and redraw the rest of the circuit.

By: Ernesto

Ernesto — Wed, 25 Feb 2009 15:18:40 +0000

Thanx for this circuit!!!! Did you ever saw the file Mike posted? I can’t access it now.

Thank you

Ernesto

By: Docent

Docent — Sat, 25 Aug 2007 20:53:24 +0000

Hi Keith,

First of all, keep up the good work, your blog is full of great projects and ideas.

I encountered exactly the same problem while preparing my bachelor thesis (I am building a mobile robot). I am using MPC17531 for motor control because my main power supply is 3.3V. If I were using L293D I could have attached PWM to EN input but this was not the case, so I needed the same circuit you described.

Turns out you can do it with a quad NOR gate. If you want to check it out (maybe you’ll need this again) I have uploaded part of my not yet finished BT here: http://files-upload.com/files/459083/main.pdf (sorry for using upload service)

Regards,
Mike