High Low Voltage Cutout Without Timer

This inexpensive circuit
can be connected to an air-conditioner/fridge or to any other
sophisticated electrical appliance for its protection. Generally, costly
voltage stabilizers are used with such appliances for maintaining
constant AC voltage. However, due to fluctuations in AC mains supply, a
regular ‘click’ sound in the relays is heard. The frequent
energisation/de-energisation of the relays leads to electrical noise and
shortening of the life of electrical appliances and the
relay/stabilizer itself. The costly yet fault-prone stabiliser may be
红包扫雷苹果下载地址 replaced by this inexpensive high-low cutout circuit with timer.

The circuit is so designed that relay RL1 gets energised when the
mains voltage is above 270V. This causes resistor R8 to be inserted in
series with the load and thereby dropping most of the voltage across it
and limiting the current through the appliance to a very low value. If
the input AC mains is less than 180 volts or so, the low-voltage cut-off
circuit interrupts the supply to the electrical appliance due to
energisation of relay RL2. After a preset time delay of one minute
(adjustable), it automatically tries again. If the input AC mains supply
is still low, the power to the appliance is again interrupted for
another one minute, and so on, until the mains supply comes within
limits (>180V AC).


Circuit diagram

The AC mains supply is resumed to appliance only when it is above
the lower limit. When the input AC mains increases beyond 270 volts,
preset VR1 is adjusted such that transistor T1 conducts and relay RL1
energises and resistance R8 gets connected in series with the electrical
appliance. This 10-kilo-ohm, 20W resistor produces a voltage drop of
approximately 200V, with the fridge as load. The value and wattage of
resistor R8 may be suitably chosen according to the electrical appliance
to be used. It is practically observed that after continuous use, the
value of resistor R8 changes with time, due to heating. So adjustment of
preset VR1 is needed two to three times in the beginning.

But once it attains a constant value, no further adjustment is
required. This is the only adjustment required in the beginning, which
is done using a variac. Further, the base voltage of transistor T2 is
adjusted with the help of preset VR2 so that it conducts up to the lower
limit of the input supply and cuts off when the input supply is less
than this limit (say, 180V). As a result, transistor T3 remains cut off
(with its collector remaining high) until the mains supply falls below
the lower limit, causing its collector voltage to fall. The collector of
transistor T3 is connected to the trigger point (pin 2) of IC1. When
the input is more than the lower limit, pin 2 of IC1 is nearly at +Vcc.

In this condition the output of IC1 is low, relay RL2 is
de-energised and power is supplied to the appliance through the N/C
terminals of relay RL2. If the mains supply is less than the lower
limit, pin 2 of IC1 becomes momentarily low (nearly ground potential)
and thus the output of IC1 changes state from ‘low’ to ‘high’, resulting
in energisation of relay RL2. As a result, power to the load/appliance
is cut off. Now, capacitor C2 starts charging through resistor R6 and
preset VR3. When the capacitor charges to (2/3)Vcc, IC1 changes state
from ‘high’ to ‘low’. The value of preset VR3 may be so adjusted that it
takes about one minute (or as desired) to charge capacitor C1 to
红包扫雷苹果下载地址 (2/3)Vcc.

Relay is now de-energised and the power is supplied to the appliance
if the mains supply voltage has risen above the lower cut-off limit,
otherwise the next cycle repeats automatically. One additional advantage
of this circuit is that both relays are de-energised when the input AC
mains voltage lies within the specified limit and the normal supply is
extended to the appliance via the N/C contacts of both relays.

Egg Timer Circuit

This egg timer, which is
both simple and functional, shows once again that it is not essential
to use a microcontroller for everything these days. The circuit consists
of only two ICs from the standard 4000 logic family, a multi-position
rotary switch and a few individual components. The combination of a 4040
oscillator/counter and a 4017 decimal counter is certainly not new, but
it is an ideal combination for timers that are required to generate
long intervals that can be programmed in steps. The circuit can be
directly powered from a 9-V battery, without using a voltage regulator.
The signalling device is a 12-V buzzer, which generally works quite well
even at a much lower voltage.

We won’t explain the operation of the two ICs here; if you would
like to know more about this, we recommend consulting the device data
sheets. The RC configuration has been selected for the oscillator
circuit of the 4060, since the frequencies of standard crystals and
resonators would be too high (even 32.768 Hz is much too high), making
it impossible to achieve the desired times. With an RC oscillator, it’s
also easier to modify the times to suit our purposes. For instance, if
the oscillator frequency is reduced by a factor of two, we obtain a
range of 1 to 16 minutes in steps of 1 minute. The range is split into
two by taking advantage of the fact that the 4017 has an AND红包扫雷苹果下载地址 gate at its input (with an inverted input).

The two ranges overlap by two steps. The oscillator has been
dimensioned such that the 23 divider output (pin 14) has a period of 30
seconds, so IC2 receives a clock pulse every 30 seconds. This means that
the oscillator frequency must be set to 8.5333 Hz. The first output of
IC2 is active after a reset, so it cannot be used. If S1 is in position
I, pin 14 of IC2 is connected to the positive supply line. This input is
used as an enable input. Directly after the first pulse from the 4060,
the second output of IC2 goes high (which means after exactly half a
minute). The sub-sequent outputs become active in turn at intervals of
红包扫雷苹果下载地址 one clock pulse, and thus generate the states for 1 to 4.5 minutes.

In the second range (II) of S1, the ‘enable’ pin of IC2 is connected
to the 212 divider output of the 4060 (pin 1). This output goes high 4
minutes after the reset (which is why it is labelled ‘240 s’, instead of
the period time of 480 s). Since the 4060 is an asynchronous counter,
this output goes high a short time after the 23 output goes low. This
delay provides the proper condition for an extra clock pulse for the
4017. The outputs of the 4017 will thus count upwards once. This means
that the second output will become active after 4 minutes, with the rest
of the outputs becoming active after 4.5 to 8 minutes. The desired
红包扫雷苹果下载地址 timing interval is selected using switch S2.

The output of S2 is connected directly to emitter follower T1, which
energizes the buzzer when the level on the wiper of the switch is high.
At the same time, the counter of IC1 is disabled via diode D1 by
forcing the oscillator input high. The buzzer thus remains active until
the circuit is switched off. The first counter output of the 4060 is
connected to an LED (D2), which indicates that
the circuit is active and the battery not yet exhausted. The blinking
rate is approximately 0.5 Hz. The current through the LED红包扫雷苹果下载地址 is set to a modest 1mA, since this current represents the majority of the current drawn by the circuit.

This ranges from 0.5 to 1.5 mA, with the average current consumption
being approximately 1mA while the timer is running. The buzzer used in
our prototype increases the current to around 13 mA when it is
energized, but this naturally depends on the actual type used. In
principle, the circuit will work with any supply voltage between 3 and
16 V. However, the actual supply voltage should be taken into account in
selecting the buzzer. The value of the supply voltage also has a small
effect on the time interval, but in practice, the deviation proved to be
less than 5 percent – which is not likely to matter too much to the

Three Hour Timer

Manufacturers of
cordless drills generally recommend a battery charging time of three
hours. Once the charging time is up the battery must be disconnected
from the charger: if you forget to do this there is a danger of
overcharging the battery. This circuit, which sits between the charger
circuit and its battery socket, prevents that possibility: the contact
of relay Re1 interrupts the charging current when the three hours are
up. Ten LEDs show the remaining charging time
in steps of 20 minutes. The timer is reset each time power is applied
and it is then ready for a new cycle. When power is applied IC3 is reset
via C4 and R5. When the charging time has elapsed, Q9 (pin 11) goes
high, which turns the relay on and interrupts the charging current.


Circuit diagram

Since Q9 is connected to the active-low EN (enable) input, the
counter will now remain in this state. The charging time can be adjusted
from about 2 hours 15 minutes to 4 hours 30 minutes using P1. The
author set P1 to 30 kΩ, giving a charging time of 3 hours 7minutes. The
greater the resistance of P1, the shorter the charging time. The timing
of the circuit is not particularly precise, but its accuracy is entirely
adequate for the job. When adjusting the charging time it is worth
noting that the first clock cycle after the circuit is turned on (from Q0
to Q1) is longer than the subsequent ones. This is because initially
capacitor C3 has to be charged to around half the supply voltage.

Flip-Flop Timer Using 4017

This circuit shows how a 4017 CMOS
decade counter can be used to build a timer circuit. Push-button S1
will discharge capacitor C1 through resistor R2. When S1 is released, C1
will charge up through R1 causing a rising edge at the clock input of
IC1. This causes the output Q1 to go high (to the supply voltage).
Current will flow through R4 and LED D2 will
light. At the same time C2 will begin charging through preset P1 and R6.
When the voltage on C2 reaches approximately half the supply voltage it
will reset IC1. Q1 will go low, the LED will
go off and C2 will discharge through D1 and R3. The circuit will now
remain stable in this reset condition until S1 is pressed again. Preset
P1 allows the ON time of the circuit to be adjusted between 5 seconds
and 7 minutes.


Circuit diagram

The current consumption of this circuit in its reset state is only a
few micro-amps, rising to approximately 8mA mainly due to the LED current, when S1 is pressed. When power is applied to the circuit IC1, can be in an indeterminate state and the LED may be on. Pressing S1 until the LED
goes off clears this condition. Alternatively C2 may be connected to
the supply rail (as shown dotted in the diagram) this will ensure that
IC1 will always power up in a reset state. A disadvantage of this
configuration is that any noise on the supply rail will be coupled
through to the reset pin of IC1 and may affect the timing period.

Switch Timer For Bathroom Light

This 9-minute timer
switch can be used to control the light in a toilet or bathroom. The
timer is started by pushing S1 and stopped by pushing S1 again. If you
forget to turn it off, the controlled light will go off after nine
minutes. If you need the light on continuously non-stop, you need to
press S1 (turn on) and then S2 (cancellation of timer) within 9 minutes
and in this case the light will be on until you switch it off with S1.
IC1 is a is 4013 dual flip-flop. Flip flop IC1a is toggled on and off by
switch S1 and it controls the relay which is switched by FET
Q2. IC1a controls IC1b which is connected as an RS flipflop to enable
or disable IC2, a 4060 oscillator/divider. This has its timing interval
set by the components at its pins 9, 10 & 11. The relay should have
250VAC mains-rated contacts and these are connected in parallel with an
红包扫雷苹果下载地址 existing wall switch.

Switch Timer For Bathroom Light

Switch Timer For Bathroom Light

Author: Rasim Kucalovic
红包扫雷苹果下载地址 Copyright: Silicon Chip Electronics

4-Minute Shower Timer

Gone are the days when
we can afford to luxuriate under a hot shower for hours on end. Well,
maybe the showers weren’t quite that long but most people are used to
taking showers in the tens of minutes. It’s easy to lose track of time
in the shower. And it does feel nice.

Mounted in the shower

Mounted in the shower

That’s a luxury that’s no longer economically nor ecologically
sustainable. First of all, we’re short of water. In most areas of
Australia the powers-that-be keep telling us if we don’t be good boys
红包扫雷苹果下载地址 and girls and cut our water usage then we are going to run out.

(Those same powers [read politicians] that keep blaming us wasteful
consumers don’t mention that for the most part water shortages are their
fault, because they haven’t invested the necessary dollars in water
infrastructure while population has steadily increased for much of the
last half century. But let’s not get into that argument. At least not
红包扫雷苹果下载地址 right now . . .)

Second, we’re short of electric power. The power that goes to heat
the water is also in very short supply. Load shedding (ie, blackouts!)
is becoming more and more common as supply authorities attempt to cut
peak loads. Those same powers-that-be keep telling us that if we don’t
reduce our consumption of power, it’s going to get worse. (Those same
powers [read politicians] that keep blaming us wasteful consumers, etc
红包扫雷苹果下载地址 etc etc . . .)

The shower capsule

The shower capsule

Putting aside all the scare-mongering that’s going on in political
circles (my spell checker wanted to change that to circuses, which would
be perhaps more apt) it really does make sense for us, as consumers, to
try to save both water and power – if only because that means less of
our hard-earned dollars will end up in Government coffers.

one way to do both, of course, is to take shorter showers. how short?

红包扫雷苹果下载地址the 4-minute shower

Believe it or not, it is entirely possible to take a shower in four
minutes – including, if you need to, washing your hair. In fact, without
shampooing, a sub-three-minute shower is perfectly practical. People in
the bush who don’t have the luxury of hot water have been “getting”
that sort of shower for years: get in, get wet, get clean, get out!

Let’s face it – all you really need to do is get wet, soap up and
rinse off. Get wet: 30 seconds. Soap up: 60 seconds. Rinse off: 60
seconds. That’s two and a half minutes. Add another 60 seconds to
shampoo your hair and there’s your four minute shower – with 30 seconds
left over for good measure.

红包扫雷苹果下载地址ok, if you agree that four minutes is enough time, how do you go about convincing everyone in your family?

Finished PCB

Finished PCB

the st4 shower timer

This rather ingenious (and patented) design is completely automatic,
turning on about 20-30 seconds after it “hears” the first “sssshhh” of
the shower – giving you enough time to adjust the water temperature –
then beeping each minute up to the magic four minutes, at which time it
sounds an alarm.

The alarm stops when you turn the shower off. But if you try to fool
it by turning the shower off for a moment and then back on again, the
alarm will start back up again. It resets after about a minute of
no-shower-sound, ready for the next person to take their shower.

Part of the secret to this circuit is the use of the piezo buzzer:
it is not only sounds the beep/alarm, as you would expect but it is also
红包扫雷苹果下载地址 used as a “microphone” to pick up the splash sound.

There’s no on-off switch; it simply operates when it hears the
shower turn on (listening for the distinctive splashing sounds of the
water). There is an internal 3-position switch and preset pot which are
红包扫雷苹果下载地址 adjusted to give the desired sensitivity – once set, you can forget it.

There are also pots to control clock frequency and tone of alarm –
红包扫雷苹果下载地址 but these are set in the factory and should not need touching.

It’s operated by a 9V battery (alkaline preferred) which should last
for at least 12 months. Current drain, when ready to operate but
红包扫雷苹果下载地址 inactive, is comparable to that of a smoke detector – around 10-15mA.

The circuit, including the piezo, is housed on a single PC board
which fits (along with the 9V battery) into a purpose-designed two-part
case. When correctly assembled is quite waterproof. Mounted on the
shower wall it allows shower sound to enter and beeps/alarm to escape
without the circuit getting at all damp.

The case, as we said, is in two parts. These snap together to form a
nice, tight seal around the PC board, with alignment of the two parts
taken care of by pins and holes which mate. Each half of the case is
fitted with a suction cap which allows the unit to mount to any smooth
红包扫雷苹果下载地址 shower wall (or even a glass screen).

While the ST4 Shower Timer is available fully built and tested, we
are more interested in it as a kit which you assemble yourself. Even
here, most of the hard work – soldering the surface-mount components and
ICs – is already done for you. In fact, as supplied, the PC board is
红包扫雷苹果下载地址 built and tested, ready for you to put together

putting it together

Assembly is as simple as removing the backing and the centre from
the self-adhesive “donut” foam ring and sticking it, as central as
possible, onto the piezo transducer. Then similarly stick the
rectangular foam pad onto the back of the PC board (it keeps the battery
snug while preventing it shorting to or across the board), then push
红包扫雷苹果下载地址 the PC board into the bottom half of the case.


Circuit diagram

The bottom half can be identified by the slots for the transducer.
When the board is pushed fully home, the foam donut “gasket” provides a
seal in a moulded housing inside the case, preventing any water entering
the case – theoretically even if dunked.

We say theoretically because it is designed that way – but
commonsense would suggest you don’t try to prove it. Because the
transducer slots are at the bottom of the case, spray would have to be
travelling upwards to enter – possible, of course.

But the foam donut stops this water going any further. While the
transducer itself is not sealed, its internal construction means that it
is also an effective water barrier, so with the sealing donut in place,
spray cannot enter the case nor either around or through the
红包扫雷苹果下载地址 transducer.

All this means that the shower timer is for all intents and purposes
waterproof, especially from spray. Once the PC board has been pushed
home, the battery can be connected and slid down into the case,
alongside the (now insulated) back of the PC board. It should be a
relatively snug fit.

In the unlikely event that the suction caps have come off the case
halves in transit, simply slide them back into their respective slots on
each end – the photos show where they go. Slide the two halves of the
case together, ensuring that the channels which hold the suction caps
line up exactly – the pins in one half won’t mate if they don’t. The two
case halves should “snap” together and that completes construction.


If you don’t want to get wet, you can use a small unmuted FM radio,
off-station, to simulate the sound of a shower. (If your FM radio mutes
automatically, or the mute cannot be turned off, this option won’t work.
You’ll need to check it in situ – in the shower!) The FM radio will
produce predominantly white noise, which is fairly close to the sound of
a shower stream striking the bottom of the shower or bath.

Turn the radio on and the timer should give a chirping sound after
20-30 seconds (that’s the water temperature adjustment period). Then it
should beep after each minute from there, with a series of beeps (7.5
seconds on, 7.5 seconds off) at the end of four minutes. Turn the radio
off and the timer should reset.

mounting in the shower

The timer always mounts vertically, with the piezo transducer
towards the bottom. The suction caps should stick very well to any
ceramic tile, glass or other smooth surface – if necessary, give ’em a
lick first! Best position for the timer is about 300-400mm from the
floor but it should work reasonably well up to about waist height.

If you need to mount the unit higher than this, or if it doesn’t
appear to be sensitive enough, open it up and slide the switch up one
notch. Don’t mount any higher than necessary. In some very low volume
showers, (eg some gravity feeds), you might need to adjust the
sensitivity right up but this would normally be unlikely.

You should not need to adjust any of the pots – they are preset on
factory assembly. Once mounted, give it another run, this time with the
shower. It should perform in the same way as it did in your “white
noise” test.

The only time you should need to remove the unit from the wall is to
replace the battery and this could be up to a couple of years or so!
Don’t pull on the timer to remove it, slide a knife or some other thin,
红包扫雷苹果下载地址 flat object under the suction caps to break the seal.

An Accurate Reaction Timer

Add a cheap stopwatch to
this circuit to produce an accurate reaction timer. The circuit is
wired in parallel with the start/stop button in the watch via a 2.5mm
socket, which fits snugly in one corner of the casing. The person
conducting the test (the “tester”) resets the stopwatch and turns on the
reaction timer’s power switch (S3). The person being tested (the
“subject”) places his or her fingers near the “STOP” push-button switch (S4). Next, the tester covertly sets a delay time with VR1 and selects either the LED or buzzer alarm via S2. To initiate the sequence, the tester then presses the “START
switch (S1). This triggers 555 timer IC1, which is wired as a
monostable. Its output (pin 3) goes high for 2-12 seconds as determined
by the setting of VR1. At the end of this delay pin 3 goes low and
triggers IC2, another 555 timer in monostable mode.

An Accurate Reaction Timer Circuit

An Accurate Reaction Timer Circuit Diagram

The output from IC2 (pin 3) activates the alarm (buzzer or LED)
for about 0.5s. After inversion by Q1, it also triggers IC3, another
555 monostable. The positive pulse from IC3 turns on Q2, briefly closing
the start/stop switch circuit in the watch. The watch starts to count
up. After a short period, the subject reacts to the alarm and pushes the
STOP” button (S4), freezing the stopwatch.
The reaction time can then be read off with 1/100th of a second
accuracy. Comparative reaction times could be measured when a subject
is: rested or tired, silent or talking, before or after a night out,
using a mobile phone, etc. For motoring realism, rig up dummy
accelerator and brake pedals, with the brake switch making the stop
contact. Or take it to your club and test people as they enter and after
they’ve been “steadying their nerves” at the bar.

author: a. j. lowe – copyright: silicon chip electronics

Telephone Ringer Using Timer ICs

Using modulated
rectangular waves of different time periods, the circuit presented here
produces ringing tones similar to those produced by a telephone. The
circuit requires four astable multivibrators for its working. Therefore
two 556 ICs are used here. The IC 556 contains two timers (similar to
555 ICs) in a single package. One can also assemble this circuit using
four separate 555 ICs. The first multivibrator produces a rectangular
waveform with 1-second ‘low’ duration and 2-second ‘high’ duration. This
waveform is used to control the next multivibrator that produces
another rectangular waveform. A resistor R7 is used at the collector of
transistor T2 to prevent capacitor C3 from fully discharging when
transistor T2 is conducting. Preset VR1 must be set at such a value that
two ringing tones are heard in the loudspeaker in one second.

The remaining two multivibrators are used to produce ringing tones
corresponding to the ringing pulses produced by the preceding
multivibrator stages. When switch S1 is closed, transistor T1 cuts off
and thus the first multivibrator starts generating pulses. If this
switch is placed in the power supply path, one has to wait for a longer
time for the ringing to start after the switch is closed. The circuit
used also has a provision for applying a drive voltage to the circuit to
start the ringing. Note that the circuit is not meant for connection to
the telephone lines. Using appropriate drive circuitry at the input
(across switch S1) one can use this circuit with intercoms, etc. Since
ringing pulses are generated within the circuit, only a constant voltage
is to be sent to the called party for ringing.


To resemble the actual telephone ringing a 400 Hz tone is switched
on in the following sequence: 400ms on, 200ms off, 400ms on and 2000ms
红包扫雷苹果下载地址 off and then repeat.

Multipurpose Flip-Flop Timer

This particular timing circuit can be used
to time one-shot events from a few seconds to a few hours. And in
standby mode (ie, with RLY1 and LED1 off), its power consumption is very
low. The heart of this circuit is a low-cost CMOS 4011 quad NAND
gate, with IC1a & IC1b configured as a standard Set/Reset
flip-flop. Briefly pressing switch S1 to start the timing sequence pulls
pin 1 of IC1a low and, as a result, pin 3 switches high. Two things
happen while pin 3 is high: capacitor Cx begins charging via
potentiometer Rx; and (2) pin 11 of IC1d will be low, which means that
红包扫雷苹果下载地址 transistors Q3 and Q1 are both on.

As a result, both LED 1 and relay RLY1 are also on. RLY1 and LED
1 remain on until Cx has been charged up to about 70% of Vcc (ie, the
supply rail). At this point, pins 8 & 9 of IC1c are pulled high and
so its pin 10 output goes low and resets the flip-flop by applying a low
to pin 6 of IC1b. This causes pin 3 of IC1a to go low and so LED1 and
RLY1 switch off and the timing period ends. At the same time, pin 4 of
the flip-flop goes high and this turns on transistor Q2 while ever the
flip-flop is held reset. This ensures that Cx is discharged, so that the
红包扫雷苹果下载地址 circuit is ready the next time S1 is pressed.

Multipurpose Flip Flop Timer Circuit

Multipurpose Flip-Flop Timer Circuit Diagram

Diode D1 and its associated 10µF capacitor reset the flip-flop when
power is first applied, so that LED1 and RLY1 remain off until S1 is
pressed. D4 is included to protect Q1 against the back-EMF
that’s generated when the relay switches off. Choosing appropriate
values for Cx & Rx for a given time delay is straightforward. The
formula is T = 1.24 x Rx x Cx, where T is the delay time in seconds. As
an example, let’s assume that we require a time delay of 10s using a
value of 100µF for Cx. Now we just need to calculate the value of Rx as
Rx = 10s/(1.24 x Cx) = 80,645O
In this case, an 82kO resistor would be the closest value. You can use
either a fixed resistor for Rx or you can use a potentiometer (or
trimpot) which can be adjusted to give the required time delay. Note
that the value of Rx should not be any more than a few megohms. Power
for the circuit can be derived from any 12V DC source. This is then fed
to 3-terminal regulator REG1 to derive a 9V rail to power the circuitry.
The exception here is the relay circuit, which is powered from the 12V
rail. Diode D3 protects the circuit against incorrect supply polarity.

author: trent jackson – copyright: silicon chip electronics

On/Off Timer

If you need an
adjustable ‘on’ or ‘off’ time for some application, then this is the
circuit you have been looking for. A problem that often occurs when
adjusting timers is that the individual times affect each other. This
circuit completely solves this problem because the time defining
elements — both R and C — are switched over. That means that there is an
RC pair (P1 + R3 and C1) for the ‘off’ time and another pair (P2 + R4
and C2) for the ‘on’ time. The relay is not energized when there is a
logical zero at the base of T1. This same zero causes, via input pins 10
and 11 of IC1, pin 12 to be connected to pin 14 and pin 2 to pin 15 of

By contrast, a logical one (relay energized) causes pin 13 to be
connected to pin 14 and pin 1 to pin 15. With the values shown, the
oscillator period (this can be measured at pin 9 of IC2) can be adjusted
from 4 to 200 ms. Since IC2 divides the frequency by 8,192 the
resulting time period is adjustable from 32.8 seconds to 27.3 minutes.
If a shorter period of time is desired C1 (or C2) has to be reduced,
increase for a longer period.

C1 and C2 need to be film capacitors or bipolar electrolytics; if these
are not available it is possible to make one yourself by connecting two
ordinary electrolytics in series, with the positive terminals together.
The power supply voltage for the timer may range from 5 to 15V. It is
preferable that you choose the same value as the rated operating voltage
of the relay. The relay shown in the parts list is a 12-V type that is
able to switch 230 VAC at several amps.