■ Inside the Ring-A-Thing.
capacitor, and NAND gate segment.
Each network is wired to provide a time delay as per
the values of the resistors and capacitors. As the positive
voltage pulses pass through the anodes of D1 and D2,
they are dampened and a positive voltage is stored by the
capacitors. The diodes now prevent the positive voltage
charge from discharging back through their cathodes.
The input impedance of each NAND gate is so high that
voltage leaks in this manner are not considered. The only
convenient discharge path for the stored positive voltage
in the capacitors is through the resistors to ground.
The amount of charge that the capacitors can hold —
combined with the resistance values — determines the
discharge rate of the positive voltage to ground. Use the
formula R x C x . 67 = T for your timing requirements.
The component values of R1/C1 will provide approximately
12 seconds and 1.5 seconds for R2/C2 but — depending on the
4093 IC manufacturer and tolerance values of the components
used — it could be slightly different. Since there are no critical
timing considerations for circuit operation to be concerned
with, the values indicated should be sufficient with any phone
service provider as long as the timing cycle of IC1a is longer
than one ring cycle to the next, or at least eight seconds.
With a positive voltage applied to each NAND gate
timing network (IC1a and IC1b), their normal high-state
output pins go low, and remain so during the entire input
charging time. Immediately following the absence of an
input ring pulse, the capacitors will start to discharge and,
when sufficiently discharged through their respective resistors to a ground potential, their output pins go high, indicating the completion of their intended time delay cycle.
Timing circuit IC1b has output pin 4 connected directly
IC1-IC2 CMOS 4093 Quad two-input NAND Schmitt-Trigger
IC3 CMOS 4017 1-of- 10 Output Counter 
IC4 MOC3010 Triac Driver 
T1 Triac TO-220 400V/2.5A 
D1-D2-D3 1N4148 
L1 Yellow LED Indicator 
R1 8.2M 
R2-R 1M 
R 100K 
R4-R 1K 
R 47K 
R8 220 
C1-C2 2. 2 µf 
C3 1 µf 
Battery Snap 
NE1 Neon Bulb 
PC1 Cadium Sulfide Photocell 
RJ11 Phone Line Plug on Wire Lead; Strip Wire Ends
SW1 Push On/Push Off Power Switch 
SW2 SPST PushButton Switch 
SW3 SPDT two-position Switch 
All items show Jameco part numbers; www.jameco.com.
Misc: Nine-volt Duracell or Lithium battery; circuit board; IC
sockets and terminal strip (optional); 120 VAC light bulb/socket;
AC cord/plug; AC relay [see text]; wire; assembling hardware;
soldering equipment; appropriate sized enclosure. I do have a
number of pre-drilled circuit boards on hand for those interested.
Email me at firstname.lastname@example.org for info.
to clock input pin 14 of IC3 — a 4017 1-of- 10 output decoder.
With the values shown (approximately 1.5 seconds in
duration), ample time is provided to allow one input pulse to
IC3 per each complete ring cycle; in this instance, causing
#1 output pin 2 to go and remain high. At this exact
instance, the timing network of IC1a is being charged and
configured to discharge approximately 12 seconds later if
no more ring signals were input while discharging.
The IC1a time cycle provides two functions: output pin 3
is directly wired to input pin 5 of IC2b and IC3 output pin 2 (#1)
is wired to input pin 6. When both input pins to IC2b are high,
then output pin 4 goes low and immediately sets the IC2c/
IC2d NAND gate flip-flop at input pin 8. This causes IC2c
output pin 10 and input pin 12 of IC2d to go high. Output pin 3
is also wired to input pin 15 of IC3, resetting IC3 to a normal
off state immediately after the IC2c/IC2d flip-flop has been
set. This turns the light on.
With input pin 2 of IC2a high and switch SW3 in the S
position, the light will have a steady glow. If SW3 is in the F
position, then the bulb will continually flash since IC2a is
wired as a feedback oscillator in this position. Oscillation
is determined as per the R6/C3 values. Once the flip-flop
is set, the light will remain on until reset. This action can be
done in one of two ways. Pressing reset switch SW2 places
a low voltage on input pin 13 of IC2d, resetting the flip-flop.
Diode D3 prevents the low voltage from appearing at IC1c
output pin 10 while lighting the ready indicator, LED L1.
Switch SW2 provides another function of indicating if the
device is powered on. If power switch SW1 is in the on
position, it can be verified by simply pressing switch SW2,
which will light LED L1 while pressed. Otherwise, LED L1
does not light with the power off.
The other option of resetting the flip-flop is to allow
exactly four rings to be entered into IC3, in which case output pin 10 of IC3 (#4) goes high, is inverted to low by IC1c,
is passed through the cathode of D3 to pin 13 of IC2d,
which resets the flip-flop and lights the ready indicator LED
L1 during the reset time period. (Whew!)
That’s about it. The ring input counts used here have
worked out pretty well. You can select any number of rings
you like (from one to nine for either on/off activation), but
using a lower number for on and a higher number for off
seems to be more practical. Pin 13 (I) of IC3 should be
November 2009 41