This is a one-bit memory that can be used to store a simple bit of information,
such as a remote power-failure or closed-trap detector, or a touch sensor.
The circuit operates as follows: When the resistance between the alligator
clips falls, the SCR is triggered, powering ON the LED.
The SCR and LED stay in the ON state even after the applied pulse to the
input is gone. So the device "memorizes" the event.
The sensor can be a magnetic switch (reed switch), a microswitch, or a touch
switch. A simple touch switch is a metal plate wired to G2. To get best sensitivity, G1 needs a good ground. You can also use as sensor two metal plates
that are touched at the same time to trigger the circuit ON.
The circuit is powered by four AA cells and current drain is very low when the
LED is off. When the LED is on, current drain is less than 10 mA.
To reset the device you only have to toggle S1. Another way to reset the
circuit is to wire a momentary switch between the anode and cathode of the
SCR. Sensors can be wired to the device with long unshielded wires.
The schematic of the One-Event is shown in Figure l.Though R2 and R3 are
shown as fixed, you can use a 1,000,000 ohm potentiometer if you prefer. A
sensitivity adjustment will get better performance from the register.
Figure 2 shows the One-event Register, on terminal strip mounting. As it is
an experimental circuit you can also use a solderless board to install the
components.
The circuit can easily be housed into a small plastic box. Observe the positions of all the polarized components, such as the LED, SCR and power supplv.
Resistor R3 is only necessary if TlC106 is used. Other SCRs, such as the
MCRl06 and Cl06, don't require R3.
Parts List - One-Event Register
SCR - TlC106 or MCR106 Silicon Controlled Rectifier
LEDs - Red, yellow or green common
R1 - 470 ohm, 114W,5% resistor
R2 - 100,000 ohm, 114W,5% resistor
R3 - 47,000 ohm, 1/4W,5% resistor - see text
S1 - SPST slide or toggle switch
B1 -6V-fourAAcells
G1, G2 - Alligator clips
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