The timer assembly consisted of these parts:
➤ Circuit board mounted in the bezel
➤ A power transformer
➤ An electromechanical relay
➤ A solid-state relay
➤ A fuse block and connections for an interlock
Since I had the circuit schematic, it was an easy task
to lay out and connect the components. There was a tight
squeeze between the timer module and the transformer, so
I had to place the transformer a distance from the module,
making it necessary to lengthen the leads. There is no
need for an interlock so I just shorted the interlock leads
together. There was also no need for the solid-state relay,
which had been used to control the magnetron, so I just
bundled those in case they were needed in the future.
I drilled a hole for the power cord and also made an
opening to receive a socket at one end of the wooden
case. It was now a simple matter to wire the components
together. I used the electromechanical relay to supply AC
voltage to the socket. The timer assembly was held in
place with an application of glue from a glue gun. Refer to
Figure 1 for a view of the front of the completed unit.
Refer to Figure 2 for a view of the interior. Note that the
cables had to be zip tied together and anchored to the
14V - 50V - Dual H-bridges - 150
Adjustable current limiting
Three R/C inputs - serial option
Many mixing options - Flipped Bot Input
Rugged extruded Aluminum case
4. 25" x 3. 23" x 1.1”
5V - 28V
2.7“ x 1.6” x 0.75”
5V - 28V
2.7“ x 1.6” x 0.5”
(6A pk) H-bridge
5V - 20V
1.6” x .625” x 0.25”
Closed-loop control of two motors
Full PID position/velocity loop
Trapezoidal path generator
Giant Servo Mode!
C source for routines provided
H-bridges: Use with Dalf or with your Micro/Stamp
3 wire interface
current & temp
We also do consulting!
Give us a call for a custom
motor control to meet your
3 wire interface
www.robotpower.com THE USA
Phone: 253-843-2504 firstname.lastname@example.org
case so that there was no
interference closing the lid.
Does it work? You
betcha! The power level
function does not work, as
there is no solid-state relay. The
electromechanical relay was used
in the original unit to control the
fan. The contacts are rated for 10
amperes so there will be no problem there.
I had also replaced the original 20 ampere fuse with a
three ampere fuse in the fuse block. I tested the timer by
turning a desk lamp on and off.
I didn't supply the usual schematic or parts list as this
project is unique. It shows what can be done with surplus
or recycled components. I expect that those who have the
inclination to build a darkroom timer will find materials
that are significantly different from what I have used. You
have to use your native intelligence. Not everything has to
be thrown out and this helps our planet in a small way.
And, it does the job! NV
What interesting things have you made out of recycled
components pulled from electronics whose best days are
behind them? Share your “recycled” creations with other
readers and enter our Recycled Projects contest.
For details, go to www.nutsvolts.com.
June 2009 45