I am going to have JLPCB make some PCBs for me. They cost only $2 each but
DHL shipping from China is $25 so it makes sense to wait until I have
several projects ready and give then a batch of designs. They populate the
board now for the price of the components, so it is a great deal. They do
all the SMT soldering for you.
Two things might interest people here, a USB connected pendant and a
hardware switch debouncer.
The switch debouncer will handle 6 switches, it accepts a raw switch and
outputs a reliably debounced signal. It will use an RC lowpass filter and
a 74HC014 Schmitt trigger. With an LED for each switch. Yes, you can do
the debounce in software but this will handle the noise with hardware. I'm
still deciding about connectors. Screw terminals or JST? Or both.
The pendant is more complex and I'm not sure of the details but here are
proposed features:
- It will connect with USB.
- There are three knobs. All are of the continuous rotation type with
A/B quadrature output.
- The main knob is a CNC "MPG" handwheel with 100 "clicks" per
revolution.
- The other two are much smaller with about 20 clicks per
revolution and also a push-button click operation, like on a car radio.
These two knobs replace the more common selector switches.
- There is a character-only LCD screen that can display four lines of
text, 20 characters long
- There are no labels printed on the front panel. The current function
of the two small knobs is displayed on the last line of the LCD
The goal is first off a "clean look" with both low complexity and
open-ended design. I think using a character display and rotary controls
does this. This pendant could run a 6 axis robot arm or a lathe depending
on the programming.
*One question: Does a pendant need a "activate" button* on the side such
that the controls are disabled if you don't hold the button down. You
don't want to jog a mill by accident if the wheel is bumped.
I'm making this for myself but I'm designing this as if it were an actual
product. So I ask "What would be useful?
I've decided I don't like the idea of a standard red E-Stop button because
someone might confuse it with the hard-wired kind. USB can not support
that. But I do want a way to quickly stop the machine. I think pressing
both small knobs at the same time will stop and re-set everything. It will
set the e-stop hal pin and reset the pendant to default. (Yes e-stop could
fail if there is a bug in the software)
[image: Simple Pendant v2.jpg]
Chris Albertson
Redondo Beach, California
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