If you want to set Eagle CAD to display units in either metric or imperial, there is a simple command to do this.
SET Interface.PreferredUnit n
where n can be: 0 - the default value. Eagle decides if will display metric or imperial 1 - imperial 2 - metric
To change current units in Eagle CAD, simply paste the command in the command line, replace the n with your preferred value and press enter. To confirm that it worked, open the DRC window.
If you have a bunch of salvaged Zener diodes you need a quick way to sort
them. In this article I describe how to build a simple test equipment that can
be used to measure the breakdown voltage of a Zener diode. It can also be used
to test LEDs and their color, since sometime a color LED can look white when
not lit. This Zener tester is powered from a 9V battery so it doesn't involve
dangerous mains voltage and can measure diodes up to 90V with the help of a
555 timer boost converter.
I also use it for checking for burned LEDs in a mains light bulb.
Main Features
Constant 5mA test current
Supports diodes up to 90V
Powered from 9V battery making it safe and portable
Can measure SMD components
Has quick connect terminals for voltage and current display
Cheap to build
Protection on shorted and open (no load) terminals
Can test a string of LEDs even in a mains light bulb
How to build a zener and LED diode tester
*DUT = Device Under Test or Diode
Under Test
Starting from left to right we have a 9V battery as a power supply and an
external power switch (the red one in the above image). When the power switch
is on the red LED is on. At this point the circuit draws 4mA. The zener diode
D2 was added in series with the LED power indicator so when the input voltage
drops bellow 5 volts, the red LED turns off and the battery needs replacement.
S1 is a momentary push button and is used to power the rest of the circuit
when pressed. This TEST button should be pushed after the DUT is connected and
only for a few seconds until the voltage on the multimeter is stable. This is
for a few reasons: the inductor L1 will get a bit warm and to prevent the
battery consumption.
A 555 timer IC is used to boost the voltage. The role of R2, R3 and C2 are to
set the output frequency. With this setup the input current when the TEST
button is pressed is 110mA. By making the resistors or capacitor a higher
value, the frequency will decrease and so the power consumption. With 2.2K
resistors and 100n capacitor the input current was 270mA! Even 110mA is a bit
higher for a 9V battery but it only draws this current when the test button is
pressed. C3 and C4 are decoupling capacitors for removing voltage noise.
When the power mosfet Q1 is on, inductor L1 will store energy in the form of a
magnetic field. When the mosfet is off, the magnetic field collapses producing
a higher voltage that will charge C5 and C6 through D3. D3 should be a
Schottky diode but I didn't had one. Capacitors C5 and C6 must be rated for at
least 100V and have low ESR. I've used two in parallel for a higher
capacitance and lower ESR.
R5 is used to discharge the capacitors.
D5 is a zener diode for clamping the voltage to 100V.
The clamping voltage must be lower than the rated voltage of the output
capacitors. I used 3 Zeners in series. I had 30V + 30V + 32V = 92V.
CON5 is a quick connect terminal with springs used mainly for speakers. The
connector has two pairs of red and black connectors. The right pair is used to
connect the leads of a voltmeter and on the left pair can be connected a
ammeter for checking the test current. J1 in a two pin jumper. When a current
meter is connected the jumper bar needs to be pulled out and mounted back when
the current meter is not connected.
CON6 and CON7 are two thick pins used to connect two alligator clips to them.
The DUT is connected across them. PAD1 is just a copper pad used to test SMD
diodes. At the end of the video you can see a 0805 LED tested.
The current control circuit
Since all datasheets specifies a 5mA test current for Zener diodes, we need a
way to maintain a constant current on all voltage ranges. Or almost, since at
higher voltages the current will decrease bellow 5mA since the battery can't
supply much current.
I've used the LM358 dual op-amp because was all I had but any single op-amp
will do. U2.2 is the unused op-amp and according to what I've read online, an
unused op-amp should not be left floating since it can cause noise, high
consumption and even internal chip damage. Instead, the non-inverting input
should be connected at a voltage between GND and VCC and the inverting input
is connected to the output.
U2.1 is the op-amp that controls the transistor Q3 which is a general purpose
NPN transistor and acts like a variable resistor to keep the current at about
5mA. R7 is a 200 ohm resistor for monitoring the current. When 5mA passes
through R7 a voltage of 1V will be across it. This voltage is monitored by the
op-amp.using the inverting (-) input. The non-inverting (+) input
monitors the voltage drop of diode D4. R4 provides enough current to cause a
1V voltage drop across diode D4. And since an op-amp is trying to keep its
inputs at the same potential, it will keep the transistor Q3 in a linear
region changing its "resistance" and so we have a steady current through the
DUT.
C7 is just a decoupling capacitor for the op-amp.
The enclosure
The box is made out of a sheet of plastic named Guttagliss. The battery is
held inside by electrical tape.
The PCB is rested against two plastic tabs glued on both sides with the
distance from the top equal with the PCB thickness
The nuts for the scews have been inserted by pushing them with a
soldering iron
I had a broken Indesit WIE 107 washing machine and I was curious to know how water is distributed to 3 containers with only 2 solenoid valves and so I took it apart.
Washing machine water inlet distribution box teardown
Top side (original)
Top side (with markers)
In the first image, the water routes from the two solenoid valves are marked with blue and red colors. Because the water jet is under pressure, it leaps over the big hole where the two streams intersect marked with yellow. When both solenoid valves are turned on, the two streams combined forms a jet at 45 degrees angle that reach to the third container. The water path is shown in yellow.
From the outside on the bottom side can be seen a third channel. Before opening I thought it got something to do with the third container but it's isolated from the other channels. The channel is marked with green color.