Amplifier Timer Circuit Schematic

Turns-off your amplifier when idle for 15 minutes, Fed by amplifier tape-output

This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting.

Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.

Circuit diagram:

Amplifier Timer Circuit Diagram

Parts:

R1,R8___________1K 1/4W Resistors
R2,R3___________4K7 1/4W Resistors
R4_____________22K 1/4W Resistor
R5______________4M7 1/4W Resistor
R6,R9__________10K 1/4W Resistors
R7______________1M5 1/4W Resistor
R10___________100K 1/4W Resistor
R11____________15K 1/4W Resistor
R12____________10M 1/4W Resistor
R13_____________1M 1/4W Resistor
R14_____________8K2 1/4W Resistor
R15_____________1K8 1/4W Resistor
C1____________470µF 25V Electrolytic Capacitor
C2,C3,C6______100nF 63V Polyester Capacitors
C4,C5__________10µF 25V Electrolytic Capacitors
D1_____Diode bridge 100V 1A
D2,D7________1N4002 100V 1A Diodes
D3__________Red LED 5mm.
D4_______Yellow LED 5mm.
D5,D6________1N4148 75V 150mA Diodes
IC1___________78L12 12V 100mA Voltage regulator IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________4060 14 stage ripple counter and oscillator IC
Q1____________BC557 45V 100mA PNP Transistor
Q2____________BC337 45V 800mA NPN Transistor
J1______________RCA audio input socket
P1_____________SPST Mains suited Pushbutton
P2_____________SPST Pushbutton
T1_____________220V Primary, 12V Secondary 3VA Mains transformer
RL1___________10.5V 270 Ohm Relay with SPST 5A 220V switch
PL1____________Male Mains plug
SK1__________Female Mains socket

Notes:

• Simply connect left or right channel tape output of your amplifier to J1.
• You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.
• The delay time can be varied changing R13 and/or C6 values.
• Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.

Source:Extremecircuits.net

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Up/Down Timer For A Power Antenna

This up/down timer was designed to control a power antenna on a late-model vehicle. Normally, this vehicle uses a body computer to control the antenna. However, the person who owned the vehicle wanted to install his own high-powered audio stereo system. The original stereo system was tied in with the body computer and this meant that a separate antenna controller was required for the after-market sound system. Also, the power antenna fitted did not have limit switches inside, hence the need for a timed control circuit. Here's how the circuit works. first, assume that the radio antenna control output is not switched on - ie, the radio is switched off.

In that case, relay RLYC will be off and so relay RLYA will also be off, as is the motor. Conversely, when the radio is switched on, the radio antenna control output line switches to +12V. And when that happens, RLYC closes its contacts and applies power to the circuit. As a result, C2 (330OF) quickly charges via D4, while Q4 is biased on via D5 and R5. This ensures that Q3 and relay RLYB remain off. At the same time, Q2 is is turned on, thus turning on RLYA and applying power to the motor. This drives the antenna in the up direction. During this time, C1 charges via R2.

Circuit diagram:

When the voltage across the capacitor reaches +8.1V, Q1 turns on via ZD1 and so Q2 turns off and switches off the relay - ie, this gives the "up" timeout. Using the values shown for C1, R2 and ZD1 gives an "up" duration of approximately 6 seconds - long enough to fully extend the antenna. D1 discharges C1 (via resistor R1) when the +12V supply is later removed. When the radio is switched off (or a CD placed into the stereo unit), the radio antenna control output switches back to 0V. This does several things: first, it turns Q4 off and this allows Q3 to turn on due to the stored charge in C2. Q3 and RLYB now turn on for about six seconds - ie, while C2 discharges via R4 - and this switches power to the motor in the opposite direction to drive the antenna down. Diodes D4 and D5 are there to prevent C2 from discharging back via the circuitry around on Q1 and Q2.

Author: Peter Howarth - Copyright: Silicon Chip Electronics

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Pendulum-Controlled Clock

Here's how to build a pendulum-controlled clock which can be made really accurate. Retro? - yes, but an interesting project all the same. You'll need a spare quartz clock which must be adapted by first isolating the two pads on the chip which lead to the coil. You then have to connect wires to these pads and feed them out through a hole in the case (see SILICON CHIP, December 1996, p38, for full instructions, or October 2001, p37, for brief notes.) You'll also need a spare battery driven pendulum from another, or the same, clock. As originally used, these pendulums are for appearance only and play no role in timekeeping.

The salvaged unit should be mounted on a substantial vertical backboard. You'll find that the pendulum swings pretty fast and it must be slowed down by adding weights near the lower end. However, it's not the mass of a pendulum that controls its rate - instead, it's the distance from the support to the centre of mass that counts. The aim is to make the pendulum operate so that it takes exactly 1s for a full "to and fro" swing - ie, 0.5s "beats". Fine adjustment on mine was made by adding an adjustable (up and down) weight to the pendulum rod. This consisted of a small G-clamp fabricated from a brass strip and held by a small screw.

Circuit diagram:

Pendulum-Controlled Clock Circuit Diagram

At the bottom end of the pendulum attach an inverted T-shape aluminium vane, about 10mm wide and as thin as possible. This should be painted black. This vane is used to trigger a photo-interrupter which is attached to the backboard. The lengths of the arms of the "T" are made so that when the pendulum swings one way, the interrupter triggers - ie, the light is no longer blocked. Conversely, when the pendulum swings the other way, the vane must continue to interrupt the light. This means that, with the pendulum swinging in 0.5s beats, we get a short pulse from the photo-interrupter at 1s intervals.

This pulse is inverted by IC1a and inverted again by IC1b which then clocks IC2, a 4013 flipflop. IC2 alternately produces 1s-long pulses at its pin 12 & 13 outputs. These outputs are then fed to IC1c & IC1d respectively, where they are gated by the short pulses on pin 4 of IC1b. This produces two short pulses to drive the clock in alternate directions at 1s intervals. And that's all you need to drive the clock. Alternatively, this circuit could be a master clock and could be used to drive several slaves, all remaining in time. And model train enthusiasts could drill one or more holes in the vane to make their "railway" clocks run at what ever speed they need.

The circuit can be built on a small piece of strip board. Note that the photo-interrupter should be mounted with the photocell facing the backboard. This minimizes the risk of interference by ambient light. The photo-interrupter is available from Jaycar - Cat.ZD 1901. A footnote for horologists - if you have a clock with a Hipp butterfly escapement, you could rid yourself of the trailing arm and contact arrangement and replace it with a vane and photo-interrupter set so that as the arc of the swing becomes too small, a pulse is missed. This could then be detected by a 555 missing pulse detector circuit which would then energize the impulsing magnet.

Author: A.J Lowe - Copyright: Silicon Chip Electronics

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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 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 circuit is ready the next time S1 is pressed.

Circuit diagram:

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 follows:

• 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

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Experimental Pendulum Clock

Using this design, you can construct an electromagnetically impulsed pendulum clock with a 1-second beat. On the prototype, the pendulum rod is 115cm long with a bob adjusted to make it beat every second. It is suspended on a short piece of mainspring from a watch, which is attached to a vertical backboard with a 6mm screw. The rod extends some 15cm below the bob and is fitted with large washes at the lower end. Note that for a pendulum to beat in seconds, there must be 99.4cm distance between the support and the centre of mass of the pendulum. Between the bob and the lower end is a 5mm wide white reflector facing back.

Below the rod and 15mm to the left is the impulse solenoid, with a core but no actuator attached. The circuit comprises of four parts: (1) the sensor; (2) the counter and solenoid driver; (3) the clock driver; and (4) the clock. The sensor is built on its own small piece of strip board and is located on the centre line of the backboard behind the reflector. It utilises a Sharp IS471F infrared modulated detector (Farnell cat. 414-2860) to eliminate interference from external light sources. The infrared emitter (IRLED1) must be mounted near to the detector (IRDET1) but be masked from it.

The emitter radiates a coded signal toward the reflector. As the pendulum passes the centre line it reflects the signal back to the detector, which then gives a negative-going output pulse on pin 2. This makes the surface-mount LED (LED1) flash once. It also sends a signal to the counter and clock driver circuits on the main circuit board. Pulses from the sensor are fed into IC1, a 4020 14-stage ripple counter. The counter’s output (pin 6) goes high every 128 counts (seconds). These long duration pulses are inverted by transistor Q1 and differentiated by the 10nF capacitor and 22kO resistor, providing a narrow trigger pulse for a 7555 CMOS timer (IC2).

Circuit diagram:

Experimental Pendulum Clock Circuit Diagram

The 7555 is wired as a monostable, driving the base of transistor Q3 with a relatively short pulse width suitable for energising the impulse solenoid. LED2 flashes in unison with solenoid pulses, and can be mounted right on the solenoid as a visual aid. Pushbutton switch S2 is used to provide gentle starting pulses to get the pendulum swinging smoothly at the outset. Switch S1 resets the counter to zero. With this arrangement, the pendulum is set swinging and when it is to the left of centre, S1is pushed. Thus, the pendulum moves right to left on even numbered counts. At the 128th count, the solenoid gives a shot pull to the left just as the pendulum is passing through the centre line and moving right to left.

The distance of the solenoid below the pendulum is adjusted so that it does not jerk the pendulum but adds a gentle nudge. The clock driver circuit also derives its timing from the output of the sensor. Negative-going pulses from the sensor are inverted by Q4 before being fed into a 4013 flipflop. On the output side, pins 12 & 13 go high in turn for one second. These pulses are too long to directly drive the clock coil, so they’re logically "anded" with the short pulses from the sensor using two gates of a 4093 NAND Schmitt trigger (IC4). The outputs from these gates then drive an adapted quartz clock movement.

A suitable clock can be made from a standard quartz movement by isolating the coil and removing the battery. See SILICON CHIP, Dec. 1996, page 38 for full instructions or October 2001 page 37 for brief notes. This is an experimental clock so you may have to try various solenoids to find one that works for you. If necessary, the solenoid pulse duration can be changed by varying IC2’s timing components. If the suspension is too stiff, try impulsing at 64 beats from pin 4 of IC1, but note that the aim is to get the freest pendulum movement possible. The Synchronome and Hipp clocks were impulsed at 30-second intervals, so your clock could be even better.

In the prototype, the reflector was made from the back of an adhesive cable clip snapped on to the pendulum rod. The white back was masked to give a 5mm wide central vertical strip, giving clean, short pulses as the pendulum passes. Current drain is several milliamps, so the prototype was powered from an SLA battery fed from a float charger. A pendulum beating in seconds is called a Royal pendulum. Its length is the same as one in a typical long case (grandfather) clock.

Author: A. J. Lowe - Copyright: Silicon Chip Electronics

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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 existing wall switch.

Circuit diagram:

Switch Timer For Bathroom Light

Author: Rasim Kucalovic
Copyright: Silicon Chip Electronics

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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.

Circuit diagram:

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

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Car Headlights Timer Circuit Schematic

Pushbutton activated, Very simple circuitry

This device is a simple timer, allowing to keep on the headlights of your vehicle for about 1min. and 30sec., e.g. when accessing some dark place, without the necessity of coming back to switch-off the lights. Pushing on P1 allows C1 charging to full 12V battery supply. Therefore Q1 is driven hard-on, driving in turn Q2 and its Relay load. The headlights are thus activated by means of the Relay contact wired in parallel to the vehicle's headlights switch. RL1 remains activated until C1 is almost fully discharged, i.e.

When its voltage falls below about 0.7V. The timing delay of the circuit depends by C1 and R1 values and was set to about 1min. and 30sec. In practice, due to electrolytic capacitors wide tolerance value, this delay will vary from about 1min. and 30sec. to 1min. and 50sec. An interesting variation is to use the inside lamp as a command source for the timer. In this way, when the door is opened C1 is charged, but it will start to discharge only when the door will be closed, substituting pushbutton operation. To enable the circuit acting in this way, simply connect the cathode of a 1N4002 diode to R1-C1 junction and the anode to the "live" lead of the inside lamp. This lead can be singled-out using a voltmeter, as it is the lead where a 12V voltage can be measured in respect to the vehicle frame when the lamp is on.

Circuit diagram:

Car Headlights Timer Circuit Diagram

Parts:

R1 = 4.7K - 1/4W Resistor
R2 = 1K - 1/4W Resistors
R3 = 1K - 1/4W Resistors
C1 = 100µF - 25V Electrolytic Capacitor (See Notes)
D1 = 1N4002 - 100V 1A Diode
Q1 = BC547 - 45V 100mA NPN Transistor
Q2 = BC327 - 45V 800mA PNP Transistor
P1 = SPST Pushbutton
RL1 = Relay with SPDT 10A min. switch
Coil Voltage 12V. Coil resistance 150-600 Ohms

Notes:

• The Relay contact must be rated at 10A or more.
• Time-delays obtained trying different tolerance electrolytic capacitors for C1:
• 100µF = 1'30" to 1'50"
• 47µF = 0'45" to 1'05"
• 220µF = 3'15" to 4'15"

Source:Extremecircuits.net

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Long Delay Timer Circuit Diagram

Suitable for battery-operated devices, Fixed 35 minutes delay

This timer was designed mainly to switch off a portable radio after some time: in this way, one can fall asleep on the sand or on a hammock, resting assured that the receiver will switch off automatically after some time, saving battery costs.

Circuit operation:

R1 and C1 provide a very long time constant. When P2 is momentarily closed, C1 discharges and the near zero voltage at its positive lead is applied to the high impedance inputs of the four gates of IC1 wired in parallel. The four paralleled gate outputs of the IC go therefore to the high state and the battery voltage is available at Q1 Emitter.
When P2 is released, C1 starts charging slowly through R1 and when the voltage at its positive lead has reached about half the battery voltage, the IC gate outputs fall to zero, stopping Q1.
This transistor can directly drive a portable radio receiver or different devices drawing a current up to about 250mA. Connecting a Relay across the Emitter of Q1 and negative ground, devices requiring much higher voltage and current operation can be driven through its contacts.

Pushing on P2 for 1 to 5 seconds, the circuit starts and then will switch off after about 35 minutes. This time delay can be varied by changing R1 and/or C1 values. P1 will stop the timer if required.
LED D1 is optional and can be useful to signal relay operation when the load is placed far from the timer.

Circuit diagram:

Parts:

R1______________10M 1/4W Resistor
R2_______________4K7 1/4W Resistor
R3_______________1K 1/4W Resistor (Optional, see Text)
C1_____________220µF 25V Electrolytic capacitor
D1______________LED any type and color (Optional, see Text)
D2___________1N4148 75V 150mA Diode (Optional, see Text)
IC1____________4011 Quad 2 Input NAND Gate CMos IC (See Notes)
Q1____________BC337 45V 800mA NPN Transistor
P1,P2__________SPST Pushbuttons
RL1___________Relay with SPDT 2A @ 230V switch (Optional, see Text)
Coil Voltage 12V - Coil resistance 200-300 Ohm

Notes:

• A 4011 Quad 2 Input NAND Gate was used for IC1, but many other CMos gates or inverter arrays can be used in its place, e.g. 4001, 4002, 4025, 4012, 4023, 4049, 4069. With these devices, all inputs must be tied together and also all outputs, as shown in the Circuit diagram.
• The operating voltage of this circuit should lie in the 6 - 12V range.

Source: www.RedCircuits.com

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One second Audible Clock Circuit Schematic

Accurate, finger-operated portable unit, 3 - 12V Battery supply

This accurate one-pulse-per-second clock is made with a few common parts and driven from a 50 or 60 Hertz mains supply but with no direct connection to it. A beep or metronome-like click and/or a visible flash, will beat the one-second time and can be useful in many applications in which some sort of time-delay counting in seconds is desirable. The circuit is formed by a CMos 4024 counter/divider chip and 3 diodes, arranged to divide the frequency of the input signal at pin #1 by 50 (or 60, see Notes).

The input impedance at pin #1 is very hight, so simply touching the pin (or a short track or piece of wire connected to it) is usually enough to provide the necessary input signal. Another way to provide an input signal consists in a piece of wire wrapped several times around any convenient mains cable or transformer. No other connection is necessary.


Circuit diagram:

One second Audible Clock Circuit Diagram

Parts:

R1 = 10K
R2 = 47.K
R3 = 100R
C1 = 1nF-63V
C2 = 10µF-25V
C3 = 100nF-63V
D1 = 1N4148
D2 = 1N4148
D3 = 1N4148
D4 = LED-(Optional, any shape and color, see Notes)
D5 = 1N4148-75V 150mA Diode (Optional, see Notes)
Q1 = BC337-45V 800mA NPN Transistor
IC1 = 4024-7 stage ripple counter IC
BZ1 = Piezo sounder (incorporating 3KHz oscillator)
SPKR = 8 Ohm, 40 - 50mm diameter Loudspeaker (Optional, see Notes)
SW1 = SPST Toggle or Slide Switch (Optional, see Notes)
B1 = 3 to 12V Battery (See Notes)

Notes:

• To allow precise circuit operation in places where the mains supply frequency is rated at 60Hz, the circuit must be modified as follows: disconnect the Cathode of D1 from pin #11 of IC1 and connect it to pin #9. Add a further 1N4148 diode, connecting its Anode to R1 and the Cathode to pin #6 of IC1: that's all!
• The circuit will work fine with battery voltages in the 3 -12V range.
• The visual display, formed by D4 and R3 is optional. Please note that R3 value shown in the Parts list is suited to low battery voltages. If 9V or higher voltages are used, change its value to 1K.
• If a metronome-like click is needed, R2 and BZ1 must be omitted and substituted by the circuit shown enclosed in dashed lines, right-side of the diagram.
• Stand-by current drawing is negligible, so SW1 can be omitted.

Source:Extremecircuits.net

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Building A Synchronous Clock

The quartz clocks which have dominated time-keeping for the past 20 years or so have one problem: their errors, although slight, are cumulative. After running for several months the errors can be significant. Sometimes you can correct these if you can slightly tweak the crystal frequency but otherwise you are forced to reset the clock at regular intervals. By contrast, mains-powered synchronous clocks are kept accurate by the 50Hz mains distribution system and they are very reliable, except of course, when a blackout occurs.

This circuit converts a quartz clock to synchronous mains operation, so that you can have at least one clock in your home which shows the time. First, you need to obtain a quartz clock movement and disassemble it down to the PC board. For instructions on how to do this, see the article on a "Fast Clock For Railway Modellers" in the December 1996 issue of SILICON CHIP. Then isolate the two wires to the clock coil and solder two light duty insulated hookup wires to them (eg, two strands of rainbow cable). Drill a small hole in the clock case and pass the wires through them. Then reassemble the clock case.

Circuit diagram:

A Synchronous Clock Circuit Diagram

To test the movement, touch the wires to the terminals of an AA cell, then reverse the wires and touch the cell terminals again. The clock second hand should advance on each connection. The circuit is driven by a low voltage AC plug pack. Its AC output is fed to two bridge rectifiers: BR1 provides the DC supply while BR2 provides positive-going pulses at 100Hz to IC1a, a 4093 NAND Schmitt trigger. IC1a squares up the 100Hz pulses and feeds them to the clock input of the cascaded 4017 decade counters. The output at pin 12 of IC3 is 1Hz.

This is fed to IC4, a 4013 D-type flipflop, which is connected so that its two outputs at pins 12 & 13 each go positive for one second at a time. As these pulses are too long to drive the clock movement directly, the outputs are each fed to 4093 NAND gates IC1b & IC1c where they are gated with the pin 3 signal to IC4. This results in short pulses from pins 3 & 10 of IC1 which drives the clock via limiting resistor R1. The value of R1 should be selected on test, allowing just enough current to reliably drive the clock movement.
Author: A. J. Lowe - Copyright: Silicon Chip

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Jogging Timer Circuit Diagram

3V Battery powered, Beeps after a fixed minutes delay

This circuit was developed since a number of visitors of this website requested a timer capable of emitting a beep after one, two, three minutes and so on, for jogging purposes. As shown in the circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thing happens after a 2 minutes delay, and so on, reaching a maximum interval of 9 minutes in position 9.

Circuit diagram:

Parts:

R1_____________47K 1/4W Resistor
R2_____________10M 1/4W Resistor
R3______________1M 1/4W Resistor
R4_____________12K 1/4W Resistor (see notes)
C1,C3__________10µF 25V Electrolytic Capacitors
C2____________100nF 63V Polyester Capacitor
D1___________1N4148 75V 150mA Diode
IC1____________4093 Quad 2 input Schmitt NAND Gate IC
IC2____________4060 14 stage ripple counter and oscillator IC
IC3____________4017 Decade counter with 10 decoded outputs IC
Q1____________BC337 45V 800mA NPN Transistor
SW1___________1 pole 9 ways Rotary Switch (see notes)
SW2___________SPST Slider Switch
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
B1____________3V Battery (two 1.5V AA or AAA cells in series etc.)

Notes:

1. Needing only one time set, rotary switch can be replaced by an hard-wired link.
2. A DIP-Switch can be used in place of the rotary type. Please pay attention to use only one switch at a time, or the device could be damaged.
3. Varying R4 from 10K to 15K you can obtain more or less than three short beeps after the preset time delay.
4. To obtain a one-second beep only, after the preset time delay, disconnect pin 9 of IC1C from pin 9 of IC2 and connect it to pin 8 of IC1C.

Source: www.RedCircuits.com

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555 Timer Circuit With Variable On/Off Times

This circuit enables the on/off times of a 555 timer to be independently varied over a wide range. This is not possible with a conventional 555 circuit with the RC network being charged from the positive supply rail and discharged via pin 7. Instead, the capacitor at pins 2 & 6 of IC1 is charged and discharged from the output at pin 3. Furthermore, the charging and discharging circuits are different, being isolated by diodes D1 & D2.

Circuit diagram:

555 Timer Circuit Diagram With Variable On/Off Times

Therefore the capacitor at pins 2 & 6 is charged via diode D2 and trimpot VR2 and discharged via D1 and trimpot VR1. With this arrangement you can have very long on times combined with very short off times and vice versa, or you can adjust the duty cycle to exactly 50% and so on. This circuit also employs a second 555 timer (IC2) as an inverter so that complementary pulses are available, if required. If not, delete IC2.

Author: A. Davies - Copyright: Silicon Chip Electronics

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Thrifty 2Hz Clock

CMOS circuits are known for their low current consumption. This is particularly important for battery-powered circuits. Unfortunately, oscillators often require quite a bit of current. We therefore propose this oscillator circuit that has a very low current consumption (about 3 µA). The circuit is powered from a type LM334Z current source. The current has been set with R4 to about 3 µA. This is sufficient to power IC1 and the oscillator circuit around X1. The oscillator generates, with the aid of a cheap watch crystal and a few surrounding parts, a signal that is subsequently applied to the divider in the 4060 and results in a frequency of 2 Hz at pin 3 (output Q13). The level of the output pulses is a lot lower than the nominal 5-V power supply voltage (IC1 is after all powered from a current source with very low current). That is why the signal on pin 3 of IC1 is amplified and inverted by T1. IC3a finally turns it into a proper square wave with acceptably steep edges.

Circuit diagram:

Thrifty 2-Hz Clock Circuit Diagram

Source:Extremecircuits.net

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A Tan Timer Circuit Diagram

Six timing positions suited to different skin types, Timing affected by sunlight intensity

This timer was designed for people wanting to get tanned but at the same time wishing to avoid an excessive exposure to sunlight. A Rotary Switch sets the timer according to six classified Photo-types (see table). A Photo resistor extends the preset time value according to sunlight brightness (see table). When preset time ends, the beeper emits an intermittent signal and, to stop it, a complete switch-off of the circuit via SW2 is necessary.
Circuit diagram:

Tan Timer Circuit Diagram

Parts:

R1 = 47K - 1/4W Resistor
R2 = 1M - 1/4W Resistor
R3 = 120K - 1/4W Resistors
R4 = Photo resistor (any type)
R5 = 120K - 1/4W Resistors
C1 = 10µF - 25V Electrolytic Capacitors
C2 = 220nF - 63V Polyester Capacitor
C3 = 10µF - 25V Electrolytic Capacitors
D1 = 1N4148 - 75V 150mA Diodes
D2 = 1N4148 - 75V 150mA Diodes
Q1 = BC337 - 45V 800mA NPN Transistor
B1 = 3V Battery (two 1.5V AA or AAA cells in series)

IC1 = 4060 - 14 stage ripple counter and oscillator IC
IC2 = 4017 - Decade counter with 10 decoded outputs IC
SW1 = 2 poles 6 ways Rotary Switch (see notes)
SW2 = SPST Slider Switch
BZ1 = Piezo sounder (incorporating 3KHz oscillator)

Photo-type	Features	Exposure time
I & children	Light-eyed, red-haired, light complexion, freckly	20 to 33 minutes
II	Light-eyed, fair-haired, light complexion	28 to 47 minutes
III	Light or brown-eyed, fair or brown-haired, light or slightly dark complexion	40 to 67 minutes
IV	Dark-eyed, brown-haired, dark complexion	52 to 87 minutes
V	Dark-eyed, dark-haired, olive complexion	88 to 147 minutes
VI	The darkest of all	136 to 227 minutes
Note that pregnant women belong to Photo-type I

Notes:

• Needing only one time set suitable for your own skin type, the rotary switch can be replaced by hard-wired links.
• A DIP-Switch can be used in place of the rotary type. Please pay attention to use only one switch at a time when the device is off, or the ICs could be damaged.

Source:Extremecircuits.net

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A Very Useful Timed Beeper Circuit Schematic

Beeps 7.5 seconds after a preset time, Adjustable time settings: 15s. 30s. 1min. & others

This circuit is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it is a modern substitute for the old sandglass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.
Circuit diagram:

Timed Beeper Circuit Diagram

Parts:
R1 = 220R
R2 = 10M
R3 = 1M
R4 = 10K
R5 = 47K
C1 = 100nF-63V
C2 = 22µF-25V
D1 = 1N4148
D2 = 3mm. Red LED
Q1 = BC337
P1 = SPST Pushbutton (Start)
P2 = SPST Pushbutton (Reset)

PS = Piezo sounder (incorporating 3KHz oscillator)
B1 = 3V Battery (2 AA 1.5V Cells in series)
IC1 = CD4081 Quad 2 input AND Gate IC
IC2 = CD4060 14 stage ripple counter and oscillator IC
SW1 = 4 ways Switch (See notes)

Circuit operation:
Pushing on P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is around 4Hz. LED D2, driven by IC1A & B, flashing at the same oscillator frequency, will signal proper circuit operation. SW1 selects the appropriate pin of IC2 to adjust timing duration:

• Position 1 = 15 seconds
• Position 2 = 30 seconds
• Position 3 = 1 minute
• Position 4 = 2 minutes

When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push on P2.

Notes:

1. SW1 can be any type of switch with the desired number of ways. If you want a single fixed timing duration, omit the switch and connect pins 9 & 13 of IC1 to the suitable pin of IC2.
2. The circuit's reset is not immediate. Pushing P2 forces IC2 to oscillate very fast, but it takes some seconds to terminate the counting, especially if a high timer delay was chosen and the pushbutton is operated when the circuit was just starting. In order to speed the reset, try lowering the value of R5, but pay attention: too low a value can stop oscillation.
3. Frequency operation varies with different brand names for IC2. E.g. Motorola's ICs run faster, therefore changing of C1 and/or R3 values may be necessary.
4. You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
5. An on-off switch is not provided because when off-state the circuit draws no significant current.

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A Bedside Lamp Timer Circuit Schematic

30 minutes operation, Blinking LED signals 6 last minutes before turn-off

The purpose of this circuit is to power a lamp or other appliance for a given time (30 minutes in this case), and then to turn it off. It is useful when reading at bed by night, turning off the bedside lamp automatically in case the reader falls asleep... After turn-on by P1 pushbutton, the LED illuminates for around 25 minutes, but then it starts to blink for two minutes, stops blinking for two minutes and blinks for another two just before switching the lamp off, thus signaling that the on-time is ending. If the user want to prolong the reading, he/she can earn another half-hour of light by pushing on P1. Turning-off the lamp at user's ease is obtained by pushing on P2.
Circuit diagram:

A Bedside Lamp Timer Circuit Diagram

Parts:
Resistors
R1 = 1K
R2 = 4K7
R3 = 10M
R4 = 1M
R5 = 10K

Capacitors
C1 = 470µF-25V
C2-C4100nF-63V

Semiconductors
C1 = 470µF-25V
C2-C4 = 100nF-63V
D1-D4 = 1N4002
D5 = 5mm. Red LED
IC1 = CD4012
IC2 = CD4060
Q1 = BC328
Q2 = BC547

Miscellaneous
P1,P2 = SPST Pushbuttons
T1 = 9+9 Volt Secondary 1VA Mains transformer
RL1 = 10.5V 470 Ohm Relay with SPDT 2A 220V switch
PL1 = Male Mains plug
SK1 = Female Mains socket

Circuit operation:
Q1 and Q2 form an ALL-ON ALL-OFF circuit that in the off state draws no significant current. P1 starts the circuit, the relay is turned on and the two ICs are powered. The lamp is powered by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 starts oscillating at a frequency set by R4 and C4. With the values shown, pin 3 goes high after around 30 minutes, turning off the circuit via C3. During the c6 minutes preceding turn-off.

The LED does a blinking action by connections of IC1 to pins 1, 2 & 15 of IC2. Blinking frequency is provided by IC2 oscillator at pin 9. The two gates of IC1 are wired in parallel to source more current. If required, a piezo sounder can be connected to pins 1 & 14 of IC1. Obviously, timings can be varied changing C4 and/or R4 values.

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Alarm Clock With Day Selector

This circuit disables an alarm clock on Saturdays and Sundays when people like to sleep in but enables normal operation on Mondays to Fridays so that people rise in time for work or school. The core of the circuit is a 4017 decade counter which acts as the day counter and it is used in conjunction with a desk clock which acts the alarm and a watch module with alarm function which provides one clock pulse very day to the 4017. In operation, the watch module feeds a day pulse via transistor Q3 to the clock input of IC1. This has seven outputs connected via day switches (S1-S7) and diodes D3-D9 to Q1 which disables the alarm signal to the speaker via transistor Q2. LEDs1-7 indicate the actual day (if you forget!).

Circuit diagram:

Alarm Clock With Day Selector Circuit Diagram

To set the system, set the desk clock for the correct time and for the desired alarm time (eg, 6’o’clock). The watch module is set to the correct time and its alarm set to midnight. The day counter, IC1, is set to the correct day, as indicated by the LEDs, by pushing switch S12 and closing switch S8 or S9. S8 is normally left open to conserve the battery by leaving the LEDs off. As shown on the circuit, switches S1-S7 are set to sound the alarm on Mondays to Fridays and disable it on Saturday and Sunday. However, you can change the days to suit your work habits.

Author: Rasim Kucalovic
Copyright: Silicon Chip Electronics

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