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interface is pressed, then the array is
recorded as a (sequentially numbered)
CSV file on the hard disk in a
previously designated folder. Then, the
program re-enters its idle loop waiting
for the start button to be pressed.
I know how to solder and build
hardware, and how to program; I need
advice on what modules to use.
#12104 E. D. Cooper
[#7105 - July 2010]
Sensor Matrix To Detect Objects
1. I'm looking for a low cost ($1 - $2)
optical sensor solution to detect the
presence of an object in a bin. The size
of a bin varies between 5 cm to 15 cm.
Sensor and LED light source would
therefore need to be that far apart.
2. Bins are grouped in a matrix of
eight by 20, and their status needs to
be collected periodically. What kind of
a circuit would be the easiest way to
collect the status of all bins?
Because the number of bins can
be in the hundreds, I suggest a system
that uses a webcam or a security
camera setup where many (100 or so)
bins are "watched" by a common
viewer. Object shape recognition
could be added to the software.
If the objects are metallic and the
bins are non-metallic, a printed circuit
coil(s) could be mounted under each
bin and each sequentially interrogated
as is done with a metal detector.
I don't recommend your optical
solution because of variations in
ambient light, dirt, aging, aiming,
William A. Hanger
[#8101 - August 2010]
Heating Element Control Circuit
I’m looking for a control circuit
wide temperature swings a normal
thermostat controller has. It would
need to be rated to at least 15 amps.
For example, using a 210-220F range:
1. What you are looking for is
called a "proportional temperature
controller." In such a circuit, there is a
linear band a few degrees wide in
which the power delivered to the heating element is inversely proportional
to the error in the temperature.
In this range, being a degree low
will result in say, 50% power being
supplied to the heating element, and
being a degree high will result in 25%
power. Outside of this narrow band,
the heater is either on or off.
So, when starting up, the heater
comes on full, and then as the
temperature approaches the setpoint,
the power is gradually backed off,
resulting in fast warm-up, small overshoot, and tight temperature control.
Fortunately, there are many ICs
that do this; the UA2016 from ON
Semi is one that is cheap, easy, and
2. Your real control problem is that
the 15 amp 120V heating element at
full heat needs 1,800 watts, and at
minimum heat, a linear controller
would need to waste 1,700 + watts.
You say it is a food smoker (not a
meth lab). I do not believe that the
smoker really needs full proportional
control, and a commercial controller
would be very expensive. You are
unhappy with the existing full-on-full-off thermostat control so consider this
alternative. This method is strictly
"electrical" and does not need expensive solid-state controls to be fried or
damaged by rain or lightning surges.