62 August 2017
READER - TO - READER TECHFORUM
Laser Color Choice
I want to convert a 3D printer to
a laser burning station to work with
wood veneers and leather goods.
Any advice on the best type and
color of laser to get? I’ve heard brown
wood and leather reflect more red
light and so I should use a blue laser.
#8171 Kyle Hoyos
Oil Filled Caps
I’m trying to bring an old tube
transmitter back to life. The power
supply uses oil filled capacitors,
which don't seem to have handy
replacements. Assuming that I can
change the oil to reduce the leakage
current, what kind of oil is used?
Will motor oil work, for example?
#8172 William Helm
PCB Layout Software
I am a retired Field Service
Engineer. Over a decade and a half
after early retirement from IBM, a
friend asked if an idea he had could
be built. I assured him it could.
He offered me partnership
if I would design and build a
demonstration system. I designed,
built, and programmed a system that
works just like he wanted it to. An
existing patent that I could find no
work-around for expires this year.
We'd like to have systems ready to go
before we start doing demonstrations.
Now, I need to convert my proto-board to a more compact layout to
be mass produced. The problem is
that all the design software I've found
requires that work be done online.
Not even a simple schematic design
without being on the Web.
I need recommendations for
offline software to generate a file for
use by a production service. All I'll
need is a library of templates for basic
TH mounting components. I do not
intend to put the results out in the
clouds because oftentimes when I
look to the clouds, there be vultures
#8173 T. A. Rooks
POTS Ring Generator
I need a circuit to generate 20
Hz 90 VAC to ring a POTS telephone
on a theater stage. That’s Plain Old
Telephone System vs. Pretty Advanced
New Stuff (PANS) for the younger
#1 Well, years ago when I was
involved in theater, we just connected
the ringer to regular 110V 60 Hz
utility power through an offstage
switch. You might have to futz with
the clapper spacing and spring
tension to get a good ring. We had
a regular telephone bell in a small
box which we rang; we hid it on
the stage near the set phone, which
wasn’t connected. If you want to
ring the actual bell in the phone
on stage, I’d suggest using a 1:1
isolation transformer for safety. One
time during a rehearsal when there
was a phone on set that an actor
was supposed to dial, for a spoof we
connected it to a phone line. When
the actor picked it up and heard the
dial tone, he completely lost it.
#2 To ring a POTS phone, you
can buy a Black Magic Telephone
Ringing Generator on eBay for $26.
Connect one output terminal of the
Generator to the red wire of the
POTS phone. Connect a 330 ohm
resistor to the other output terminal
of the Generator and the other end
of the resistor to the green wire of the
POTS phone. The phone should not
be connected to anything else!!!
Use a pushbutton to apply
between 4. 4 and 6 VDC to the input
terminals of the Ringing Generator
and it will ring the phone. You can
use four D cells in series to supply 6
VDC. Or a 5-6 VDC power supply.
The Generator input terminal with the
red dot should be connected to the
plus voltage. DO NOT CONNECT
THE POWER WIRES BACKWARDS!
Typically, a phone rings for two
seconds, then off for four seconds,
then on for two, off for four, etc.
Be sure to test it at home before
you use it on stage. Try to use an
older “heavy” pushbutton or rotary
telephone because it will contain real
bells and the ringing will sound better.
Apple Valley, CA
[#4173 - April 2017]
Warm Cows Are Happy Cows
My daughter is in 4H and has a
calf we are raising in a shed behind
the house. The bulb burned out on
the heat lamp we leave on to keep the
cow warm. Is there a simple circuit to
remotely monitor the temperature and
alert me if it drops below a set point?
I know there are remote temperature
gauges but I need one with an alert or
a way to hack one to add an alert.
#1 Sounds like a job for the
Raspberry Pi 3 computer connected
to a DS18B20 temperature sensor
with Cayenne software installed on
both the Raspberry Pi and mobile
phone. Cayenne is a software
platform from MyDevices that acts
as a gateway to the Internet of Things
(Io T); the service is free. You can
view temperature data from your
mobile phone, or configure Cayenne
to send a text message alert when
the temperature drops below a set
threshold. The Raspberry Pi can be
connected to your home network
using Wi-Fi or a wired connection.