|Mar 11, 2011, 06:33 AM|
Joined Nov 2003
Yes, Cam, we collectors of parts can get saturated. Many of these I have a lot of, some just a few. It's a good way to build up a pot or cap collection, spread of values. Here is a sampling:
Standard red LED .2" dia. x .3" .05
SMD red LED 0805 .05
EC103D SCR, 400V, .8A TO92 .10
GIANT red LED, 30mA .4" dia. x .5" .25
GIANT yel LED, 30mA .4" dia. x .5" .25
2.2K, 1/2W SMD resistor 2010 .05
5-12V DC beeper 1" dia. x .9" .50
6-12V DC motor, 50mA 1.1" dia. x 1.6", shaft .09" dia. .50
5-9V DC beeper .5" dia. x .4" .25
Electret mic .4" dia. x .3" .50
1.5V pager motor, with vib weight .3" dia. x .8" .50
LCD, 2 x 16, no backlight 4.8" x 1.8" 1.00
LCD, 2 x 16, with backlight 4.8" x 1.8" 2.00
PIR module, 3 leads, with data 1.x 1.4 x .7 2.00
MAKE YOUR OWN CONNECTORS! Military male/fem pin sets.
Gold plated. 2 sizes STD: dimension of mated pair = .13" x 1.5".
STD male pin is .06" dia. Take 22-14gA wire. SET of 2 fem, 1 male .10
TINY SIZE mated pair = .1" x 1.5", male pin is .04" dia. SET, 2/1 .10
16 pin DIP socket .10
18 pin DIP socket .10
PCB pushbutton, Mouser 101-0161 .2" x .3" x .2" .10
Datel meter bezel DMS-BZL2-C 2.5 x 1.3 (2 x .7 inner) .10
3/32" clear Lucite sheet (4 small holes in corners) 4.8" x 2.9 .10
10K digital pot, with 00-99 counter wheels, up/dn pushbuttons
1.1" x .9" x 1.4" 4.00
|Mar 11, 2011, 06:40 AM|
Joined Nov 2003
SCR Tech Note
Have a pile of EC103D 400V, 0.8A SCR's. A dime. They look like a normal TO-22 transistor,
2N2222 or 2N3904.
A transistor turns on with some base current, a fet by bringing the gate voltage high enough.
The SCR is like a diode, has an anode and cathode, but also a gate lead. It is a diode
you can activate! Look at it as a latching transistor, if you do it right (DC circuits).
What is it useful for? First of all, as an alarm circuit. Often there is a momentary input available,
but you want it to "stick". The SCR is a simple way to do it. Just apply enough gate current to
allow latching. Then it can go away. With a 9V source, 1K to 4.7K will work. The SCR will turn on, and stay on, as long
as the load provides enough "holding current".
This is where my problem with the piezo beeper happened. It has an internal oscillator, so runs
from DC, but did not work with the SCR!
Because the oscillator presented an ac current load, which must go pretty close to zero amps between cycles, the SCR was not happy and did not latch. All it took to fix it was a 4.7K resistor across the beeper, to cause a minimum current draw all the time.
A common app for larger devices is the CROWBAR. This is an overvoltage sensor rigged to trip the SCR if a power supply output voltage goes too high. Of course this short on the output will blow the fuse, and protect the load, hopefully. A fuse takes a few mS to open up.
Here are a few other circuits:
Mainly, this device is useful in dc circuits, for I/O, single bit memory cell, or activating the power to a module (there is no current drain until triggered). Diagrams are shown for ac apps, but really the triac is more useful there.
More on phase control, the EC103D can handle line voltage easily. And small loads.
One more thing, if you are wondering how to shut it off, you have to reduce the load current
below the holding current, to do that. On ac circuits that happens at every zero crossing of
the line voltage. On dc it sticks, which is useful sometimes.
|Mar 20, 2011, 07:53 PM|
Joined Nov 2003
Tech Note: SCHMITT TRIG AND COMPARATOR: 4584/LM311
Anyone interested, I have some 4584's for a dime. Beat that, Digikey!
If you have a slowly varying analog signal that you want to convert to a digital one,
a Schmitt Trigger will do the job. The 4584 is a six pack of them! This CMOS inverter
has a switching threshold that is one half of the supply voltage (5-15V typ). Watch out,
that threshold varies a bit with temperature, read the data sheet.
Hysteresis: This "snap action" characteristic is built into the 4584. It is internally setup
with positive feedback, to cause a rapid transition of the output, high or low, when the input
crosses the threshold. Also known as "deadband", it prevents oscillation, as when the input
level is within the deadband, nothing happens.
The LM311 comparator allows more flexibility, but some resistors must be added, for
hysteresis. A feedback R and input R (+ input). Usual values are 1M for the feedback R,
and 100K for the input R. The ratio of them controls the width of the deadband. Note that
the LM311 requires a "pullup" R on the output, 1K is OK, for 5V. Pins 1 and 4 are both grounded,
for a 0-5V range of the output, but it is possible to rig it for bipolar operation (output swings
The threshold voltage of the LM311 is applied to the - input, with a pot or voltage divider.
Note that if you do not add hysteresis, when the reference and analog input are close, or
equal, the output will oscillate, not good. Add deadband!
The 4584 is simpler, no extra parts are needed. The LM311 has more configurations, it has
a separate reference input which can be varied. You may be wondering why the LM311 output
needs a pullup R. It is an open collector output, capable of driving 50mA loads, relay coils,
lamps, etc. When using for a digital output signal, the pullup R can go to either 5V or 15V.
So it can also be used as a level translator.
Who knows what the 4584 circuit is doing? Any problem with driving LED's? What is the rate?
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