But makers can always find something useful, so I proceeded with the autopsy to find what I could immediately put to use, and what would go into my cache of parts for future projects. The electrical “guts” of the coffee maker came out in one connected clump after the removal of a few screws. Immediately useful for any one of hundreds of projects is the transformer. In most cases of scrounged electronics, you’ll find that the transformer reduces standard 110V AC line voltage to something more palatable for low- voltage electronics. Most often you’ll see a single pair of wires on the secondary (low voltage) side of the transformer. If you see 3 wires (like the one shown here), it usually means that the secondary winding is center-tapped — for example, that the voltage across the 2 outer wires would be a certain value but the voltage across either outer wire and the center wire would read half the total
value across the outer 2 wires.
A
Such was the case with this coffee maker’s
transformer, turning 9V into two 4.5V levels.
Some transformers have multiple secondary
windings. If the voltage ratings aren’t listed
on the transformer case, they can easily be
determined with a voltmeter.
Also useful for various projects is the relay.
This device allows you to switch a circuit on or
off with the voltage from another circuit. In the
case of the coffee maker relay, the low voltage
supplied by the timer circuit would control the
higher 110V AC line voltage going to the heating element. Relays have many practical uses,
including robotics. It’s always good to have a
few in your junk box.
Gregory Hayes
I didn’t have any immediate plans for the
heating element so I freed its thermostatic
switch from the clip that attached it to the
heater. In the coffee maker, this is used to
maintain the carafe’s warm state after brewing
and to prevent overheating that would damage
the unit or cause a dangerous possibility of
fire. Again, such a device can be put to work
for circuits that warn of high heat conditions.
That brings us to the timer board. Lots of
CAUTION: Be careful! If you’re not comfortable
working with voltages and currents that can harm or even
kill, either do not attempt this type of project, or seek
assistance from someone who can help you learn the
needed skills. Safety first!
great parts here that could be applied to other
designs: 6 momentary switches, 2 LEDs, 4
transistors, 5 diodes, a small digital readout,
and the ever-present capacitors and resistors.
All good for building fun things. But I backed
off stripping the board because, remember,
it’s a timer board! While it may no longer be
used to brew coffee, it can be applied to turn
many other things on and off. Coupled with the
recovered relay, it can be repurposed to control higher voltage systems as well.
While the overall part count is low, even a
castoff coffee maker can light up a maker’s
eyes like a couple of LEDs. ;
T. J. “Skip” Arey has been a freelance writer to the radio/
electronics hobby world for more than 30 years and is the
author of Radio Monitoring: The How-To Guide.
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