Relay Toggle Switch

I designed this relay circuit to function as a DPDT
toggle which is controlled by a momentary switch. I strive to keep my
circuits simple with little or no integration (555’s, transistors, etc).
红包扫雷苹果下载地址 The circuit is shown active or “on” mode.

Half of RL1 and RL2 manipulate the switching and the other is
connected to an application. Relays are 200 ohms above ground and at one
point are referenced to positive that turns them off.


RL1 (which is off) applies plus voltage from its armature and
latches RL2 “on”. The application terminals are set to [A]. The
condition changes when S1 is activated, voltage is applied to RL2
latching RL1 “on” releasing S1 turns RL2 “off”. RL2’s armature is then
directed to R1. Terminals are set to [B].

When S1 is pressed again, the relays negative side are referenced to
positive, RL1 turns “off” (there’s no current flow). RL2 turns “on”
when S1 is released, terminals are set to [A]. There is slight lag
between relays depending on how long S1 is held.

Relay Toggle Switch Circuit

Relay Toggle Switch Circuit Diagram


If different relays are used, adjustment of R1’s value may be required. For example, OEG
relays (12vdc, 270 ohm coil) need R1 at 60 – 70 ohms. The prime
motivation for this design was to avoid using toggle switches for my
audio control panel. Another plus, it can be controlled from a remote
transmitted pulse. Relays are available at

author: roland segers

Garage Door Closing Circuit Just using Relays

Because I’m old school, I
wanted to build a Garage Door Closing circuit without relying on
integrated configurations (555 timer etc) to keep it simplistic. The
circuit closes the garage door after two minutes with C3 and four
minutes with the addition of C2. The timer relay is surprisingly
accurate (+/- five seconds). Another feature is to ensure that the
garage door actually did close, such as if it’s stopped mid-operation by
红包扫雷苹果下载地址 the user.


S3 (magnetic N.C.) is located at the garage door and activates the circuit when the garage door opens.
RL1 is the reset timer. It’s maintained in the “on” position for two
minutes by C3 while the trigger capacitor, C4, is charged. RL2 is the
conduit, directing C4 to either RL3 or R1 to ground when off. Purpose of
R1 is to prevent arching across contacts and a fast discharge. RL3’s
contacts are connected to the Garage Door’s Momentary Switch and is
sustained “on” for a half second by C5.

When C3 discharges to the cutoff voltage of RL1, it turns off and
resets. C4 charges C5, which turns on RL3 and initiates the garage door.
Because C4 does not have the time to fully discharge, it should be at
least three times the value of C5. If it does not close, RL1 in
countdown mode will reset and open the door. When it resets again, the
door will close.

Turning off the circuit, C1 maintains RL1 “on” slightly longer to
ensure that RL2 is set to discharge C4 to R1. If this is not done and C4
is not discharged, the garage door will not open until it discharges
naturally and falls below the trigger voltage for RL3. The circuit
would be useless for several days.



  • Time delay of RL1 after reset drops 15 seconds because of the short charge time.
  • To boost RL3 to a one-second delay, increase C5 to 1000uF.
  • D2, D3, and D4 isolate the crucial sections of the circuit.
  • Relays do not turn off at the same rate. I conducted a test by
    tripping the circuit on and off at a high rate and discovered the
    possibility of C4 turning on RL3. The addition of C1 solved this.

红包扫雷苹果下载地址author: roland segers (

Electronic Touch Switch

Mechanical contacts have
the disadvantage that they wear out. That is why it is practical to use
an electronic ‘touch switch’ in some situations. With such a touch
switch the resistance of the human skin is used for the switching
action. The schematic shows the design of a circuit that senses the
resistance of the skin and converts it into a useful switching signal.
The touch switch contacts can be made from two small metal plates,
rivets, nails, etcetera, which are placed close together on a
红包扫雷苹果下载地址 non-conducting surface.

In this circuit a comparator of the type LM393 has been used. In the
idle state there is, via R1, a voltage equal to the power supply
voltage on the non-inverting input of IC1a. Because the inverting input
of IC1a is set with R2 and D3 to D5 at the supply voltage minus 1.8 V,
the open-collector output of IC1.a is, via R3, equal to the power supply
voltage. This voltage is inverted by IC1.b. The voltage at the
non-inverting input of IC1.b amounts to half the power supply voltage
(through voltage divider R4 and R5) and is lower than the voltage on the
inverting input.

Circuit diagram:

Electronic Touch Switch Circuit

Electronic Touch Switch Circuit Diagram

The output of IC1.b is therefore a ‘0’. If the two touch contacts
are bridged with a finger, the voltage at the non-inverting input will
become low enough to cause the comparator to toggle state. The moistness
of the skin results in a resistance of 1 to 10 MR. If this circuit is
used in the vicinity of equipment that’s connected to the mains, then it
can be sufficient to touch only the upper contact to operate the
switch, provided that the circuit has been earthed. The body then acts
as an antenna which receives the 50 Hz (or 60 Hz) from the mains.

This is enough to toggle IC1.a at the same 50 Hz. C1/R3 prevent this
50 Hz from reaching the input of IC1b and provide a useable ‘pulse’ of
about 10 s at the output of IC1.b. Note that a fly walking across the
touch switch conducts enough to generate a switching signal. So do not
operate important things with this circuit (such as the heating system
or the garage door). Do not make the wires between the touch contacts
and the circuit too long to prevent picking up interference. The power
supply voltage for the circuit is not very critical. Any regulated DC
红包扫雷苹果下载地址 voltage in the range from 6 to 20 V can be used.

author: heino peters – copyright: elektor electronics magazine

Ultra-Sensitive Solid State Clap Switch

Here is the circuit of a
highly sensitive clap switch that can be operated from a distance of up
to 10 metres from the microphone. Signals picked up by the microphone
are amplified by transistors T1, T2, and T3. Diode D1 detects clap
signals and the resulting positive voltage is applied to the base of
transistor T4. The output from transistor T4 is further amplified by
transistor T5, whose output is used to trigger a monostable
multivibrator wired around the 555 timer (IC1). The output of IC1 is
used as a clock for decade counter 4017 (IC2) that is wired as a
红包扫雷苹果下载地址 divide-by-two counter.

For each successive clap, transistor T6 conducts and cuts off
alternately. As a result, for each clap signal, the lamp is either
switched ‘on’ or ‘off’. Triac 8T44A (or ST044) can drive load of up to
4-amp rating. The 12V DC for operation of the circuit is directly
derived from the mains using rectifier diode D2, current-limiting
resistor R16, and 12V zener ZD1 shunted by filter capacitor C7.

Clap Switch Diagram

Here’s a clap switch
free from false triggering. To turn on/off any appliance, you just have
to clap twice. The circuit changes its output state only when you clap
twice within the set time period. Here, you’ve to clap within 3 seconds.
The clap sound sensed by condenser microphone is amplified by
transistor T1. The amplified signal provides negative pulse to pin 2 of
IC1 and IC2, triggering both the ICs. IC1, commonly used as a timer, is
wired here as a monostable multivibrator. Trigging of IC1 causes pin 3
to go high and it remains high for a certain time period depending on
the selected values of R7 and C3. This ‘on’ time (T) of IC1 can be
calculated using the following relationship: T=1.1R7.C3 seconds where R7
is in ohms and C3 in microfarads. On first clap, output pin 3 of IC1
goes high and remains in this standby position for the preset time.

Also, LED1 glows for this period. The output of IC1 provides supply
voltage to IC2 at its pins 8 and 4. Now IC2 is ready to receive the
triggering signal. Resistor R10 and capacitor C7 connected to pin 4 of
IC2 prevent false triggering when IC1 provides the supply voltage to IC2
at first clap. On second clap, a negative pulse triggers IC2 and its
output pin 3 goes high for a time period depending on R9 and C5. This
provides a positive pulse at clock pin 14 of decade counter IC 4017
(IC3). Decade counter IC3 is wired here as a bistable. Each pulse
applied at clock pin 14 changes the output state at pin 2 (Q1) of IC3
because Q2 is connected to reset pin 15. The high output at pin 2 drives
transistor T2 and also energizes relay RL1. LED2 indicates activation
of relay RL1 and on/off status of the appliance. A free-wheeling diode
红包扫雷苹果下载地址 (D1) prevents damage of T2 when relay de-energizes.

Momentary Switch Teamed With Latching Relay

This circuit allows an SPST momentary pushbutton to act as a push-on push-off switch, using a DPDT
latching (bi-stable) relay. It was originally intended to allow a
single pushbutton switch on the dash of a vintage car to provide a
latched function. The relay only draws current when it is being
switched. At other times, the only current drain on the 12V supply is
the leakage current of one 22µF capacitor, which is very low. It works
as follows.

Assume that initially the latching relay is in the reset state, with
pins 4 and 6 connected together. In this state, C2 charges up to +12V
via 2.2kO resistor R2 while capacitor C1 remains discharged as it is not
connected to the 12V supply. If S1 is pressed, C2 discharges via the
relay’s “set” coil, diode D2 and S1. This switches the relay into its
set position, connecting pins 4 and 8. C1 then begins to charge via R1.
While S1 is being held down, the relay does not return to the reset
position because the current supplied via R1 is insufficient for the
coil to latch the armature. As soon as S1 is released, current no longer
flows though the coil so C1 can finish charging, ready for the next
红包扫雷苹果下载地址 button press.

Momentary Switch Circuit Teamed With Latching Relay

Momentary Switch Circuit Diagram Teamed With Latching Relay

Once the relay has switched and C1 has finished charging, pressing
S1 again causes the relay to switch back to the reset state via the same
process. The unused set of relay contacts can be used as an SPST or SPDT switch. The circuit as shown has been tested with the Jaycar SY4060 relay. It will work with other DPDT
twin-coil latching relays but the resistor and capacitor values may
need to be adjusted to suit. Relays with lower resistance coils will
红包扫雷苹果下载地址 need larger value capacitors and smaller value resistors.

author: merv thomas – copyright: silicon chip electronics magazine

Handy Time Delay With Relay Output

This circuit is designed
to provide delayed relay switching action at power on. The delay is a
function of the time constant produced by the combination of R1 and C1.
At power on, C1 charges slowly via R1 and the coil of the relay. When
the voltage across C1 exceeds both the base-emitter voltage of Q1 and
the gate trigger voltage of the SCR, gate current flows. This fires the SCR
and switches on the relay. At power off, diode D1 rapidly discharges C1
through the 100O resistor, so ensuring that every time the circuit is
红包扫雷苹果下载地址 restarted, as in a temporary outage, the delay time is maintained.

Circuit diagram:

Time Delay Circuit With Relay Output

Time Delay Circuit Diagram With Relay Output

Just about any NPN transistor can be used
for Q1, since after SCR1 fires, it is effectively out of the circuit. In
fact, the only part that’s still active after SCR1 turns on is the
relay. You can’t get much simpler than that! This circuit can be used to
delay speaker turn-on, so avoiding the “thump” that occurs in some
stereo systems at power on. A 5-second delay is enough for this
application, requiring approximately 560kO for R1 and 10µF for C1.
Another application might be as a motor protector in a short power

author: r. besana – copyright: silicon chip electronics

Pushbutton Relay Selector

This circuit was
designed for use in a hifi showroom, where a choice of speakers could be
connected to a stereo amplifier for comparative purposes. It could be
used for other similar applications where just one of an array of
devices needs to be selected at any one time. A bank of mechanically
interlocked DPDT pushbutton switches is the
simplest way to perform this kind of selection but these switches aren’t
readily available nowadays and are quite expensive. This simple circuit
performs exactly the same job. It can be configured with any number of
outputs between two and nine, simply by adding pushbutton switches and
红包扫雷苹果下载地址 relay driver circuits to the currently unused outputs of IC2 (O5-O9).

Gate IC1a is connected as a relax-ation oscillator which runs at
about 20kHz. Pulses from the oscillator are fed to IC1b, where they are
gated with a control signal from IC1c. The result is inverted by IC1d
and fed into the clock input (CP0) of IC2. Initially, we assume that the
reset switch (S1) has been pressed, which forces a logic high at the O0
output (pin 3) of IC2 and logic lows at all other outputs (O1-O9). As
the relay driver transistors (Q1-Q4) are switched by these outputs, none
of the relays will be energised after a reset and none of the load
devices (speakers, etc) will be selected. Now consider what happens if
you press one of the selector switches (S2-S5, etc). For example,
pressing S5 connects the O4 output (pin 10) of IC2 to the input (pin 9)
红包扫雷苹果下载地址 of IC1c, pulling it low.

Circuit diagram:

Pushbutton Relay Selector Circuit

Pushbutton Relay Selector Circuit Diagram

This causes the output (pin 10) to go high, which in turn pulls the
input of IC1b (pin 5) high and allows clock pulses to pass through to
decade counter IC2. The 4017B counts up until a high level appears at
its O4 output. This high signal is fed via S5 to pin 9 of NAND
gate IC1c, which causes its output (pin 10) to go low. This low signal
also appears on pin 5 of IC1b, which is then inhibited from passing
further clock pulses on its other input (pin 6) through to its output
(pin 4), thus halting the counter. So, the counter runs just long enough
to make the output connected to the switch that is pressed go high.
This sequence repeats regardless of which selector switch you press, so
红包扫雷苹果下载地址 the circuit functions as an electronic interlock system.

Each relay driver circuit is a 2N7000 FET
switch with its gate driven from one output of IC2 via a 100W resistor.
The relay coil is connected from the drain to the +12V supply rail, with
a reverse diode spike suppressor across each coil. If you want visual
indication of the selected output, an optional indicator LED
and series resistor can be connected across each relay coil, as shown.
For selecting pairs of stereo speakers, we’d suggest the use of relays
like the Jaycar SY-4052. These operate from 12V and have DPDT
contacts rated for 5A. Note that although four selector switches are
shown in the circuit, only two relay drivers are shown because of
limited space. For a 4-way selector, identical relay drivers would be
driven from the O2 and O3 outputs of IC2.

红包扫雷苹果下载地址author: jim rowe – copyright: silicon chip electronics

Relay Coil Energy Saver

Some relays will become
warm if they remain energized for some time. The circuit shown here will
actuate the relay as before but then reduce the ‘hold’ current through
the relay coil current by about 50%, thus considerably reducing the
amount of heat dissipation and wasted power. The circuit is only
suitable for relays that remain on for long periods. The following
equations will enable the circuit to be dimensioned for the relay on
hand: R3 = 0.7 / I Charge time = 0.5 × R2 × C1 Where I is the relay coil
current. After the relay has been switched off, a short delay should be
allowed for the relay current to return to maximum so the relay can be
energized again at full power. To make the delay as short as possible,
keep C1 as small as possible. In practice, a minimum delay of about 5
红包扫雷苹果下载地址 seconds should be allowed but this is open to experimentation.

Circuit diagram:

The action of C2 causes the full supply voltage to appear briefly
across the relay coil, which helps to activate the relay as fast as
possible. Via T2, a delay network consisting of C1 and R2 controls the
relay coil current flowing through T1 and R3, effectively reducing it to
half the ‘pull in’ current. Diode D2 discharges C1 when the control
voltage is Low. Around one second will be needed to completely discharge
C1. T2 shunts the bias current of T1 when the delay has elapsed. Diode
D1 helps to discharge C1 as quickly as possible. The relay shown in the
circuit was specified at 12 V / 400 ohms. All component values for
guidance only.
Author: Myo Min – Copyright: Elektor July-August 2004

Simple Relay Step-Up Circuits

Have you ever needed to
power a 12-volt relay in a circuit but only had 6 or 9 volts available?
This simple circuit will solve that problem. It allows 12-volt relays to
be operated from 6 or 9 volts, or 24-volt relays from 12 volts. While
most normal relays require the manufacturer-specified coil voltage to
reliably pull the contacts together, once the contacts are together you
only need about half that rated voltage to hold them in. This circuit
works by using that principle to provide a short burst of twice the
supply voltage to move the contacts and then applies the available 6 or 9
volts to the relay to lock the contacts in place.

With reference to Figure A., when the main supply is applied to the
circuit the 220-µF capacitor, C1, charges quickly to +6 volts through
resistor R3. The circuit is now awaiting voltage on the control input.
When a control voltage (can be as little as 3 volts) is applied to the
control input, transistor T1 switches on. The other transistor, a BC558,
is also switched on. This allows connection of the relay coil to the
main supply rail while T1 shorts the positive terminal of the 220-µF
capacitor to ground. Now the negative terminal of the capacitor is at a
potential of –6 volts. This is applied to the other side of the relay
coil. The relay coil potential is then briefly 12 volts — enough to
红包扫雷苹果下载地址 actuate the contact(s).

However, the coil voltage drops to the supply voltage fairly
quickly. The period is determined by the R-C time constant of the relay
coil resistance and the 220-µF capacitor. While this circuit is simple
and works well in many situations, it has a few weaknesses in its
current form. The relay may remain energized for as long as one second
after the control input has fallen. Also, if the control input goes high
before the capacitor has fully recharged, it may not have enough energy
to control the relay reliably. Also, the voltage drop across the diode
limits the voltage to about 10.8 volts.

The more complex version of the circuit shown in Figure B fixes
these problems by using an extra transistor and diode. In this
arrangement, the BC558 is now isolated from the recharge current of the
capacitor. The new transistor provides fast charging for the capacitor.
Charging is completed within the mechanical response time of the relay.
When using these circuits it should be noted that the contact pressure
of the relay contacts may be al little lower than with the nominal coil
voltage. It is therefore advisable to keep contact currents well below
红包扫雷苹果下载地址 the maximum specified value.