Jogging Timer

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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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.

Note.

• 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 off and then repeat.

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Garage Timer Circuit Diagram

The circuit described here is a testament to the ingenuity of two young designers from  a specialist  technical secondary school. The ‘garage timer’ began as a school electronics project and has now made it all the way to publication in our Summer Circuits special issue of Elektor Electronics. The circuit demonstrates that the application possibilities for the 555 and 556 timer ICs are by no means exhausted. So what exactly is a ‘garage timer’?

When the light switch in the garage is pressed, the light in the garage comes on for two minutes. Also, one minute and forty-five  seconds  after  the  switch is pressed, the outside light also comes on for a period of one minute. The timer circuit is thus really two separate timers. Although the circuit for the interior light timer is relatively straightforward, the exterior light timer has to deal with two time intervals. First the 105 second period must expire; then the exterior light is switched on, and after a further 60 seconds the light is turned off. To realise this sequence of events, a type 556 dual timer device, a derivative of the 555, is used.

Circuit diagram:

Garage Timer Circuit Diagram

The first of the two timers triggers the second after a period of 105 seconds. The second timer is then active for 60 seconds,and it is this timer that controls the exterior light. The interior light timer is triggered at the same moment as the dual timer. In this case a simple 555 suffices, with an output active for just two minutes from the time when the switch is pressed. Push-button S1 takes over the role of the wall-mounted light switch, while S2 is provided to allow power to be removed from the whole circuit if necessary. The circuit could be used in any application where a process must be run for a set period after a certain delay has expired.

For the school project the two garage lights are simulated using two LEDs. This will present no obstacle to experienced hobbyists, who will be able to extend the circuit, for example using relays, to control proper lightbulbs. The principles of operation of type 555 and 556 timers have been described in detail previously in Elektor Electronics, but we shall say a few words about the functions of Ic1a, IC1b and IC2.

When S1 is pressed (assuming S2 is closed!) the trigger inputs of both IC1a and IC2 are shorted to ground, and so the voltage at these inputs (pins 6 and 2 respectively) falls to 0 V.  The outputs of IC1a and IC2 then go to logic 1, and D2 (the interior light) illuminates. Capacitors  C1  and  C8  now  start  to charge via P1 and R2, and R8 and P3 respectively. When the voltage on C8 reaches two thirds of the supply voltage, which happens after 120 seconds, the output of IC2, which is connected as a monostable multivibrator, goes low. D2 then goes out. This accounts for the interior light function.

Likewise, 105 seconds after S1 is closed, the voltage on C1 reaches two thirds of the supply voltage and the output of Ic1a goes low. Thanks to C4, the trigger input of IC1b now receives a brief pulse to ground, exactly as IC1a was triggered by S1. The second monostable, formed by IC1b, is thus triggered. Its pulse duration is set at one minute, determined by C5, R5 and P2. D1 thus lights for one minute. Potentiometers P1, P2 and P3 allow the various time intervals to be adjusted to a certain extent.

If considerably shorter or longer times are wanted, suitable changes should be made to the values of C1, C5 and C8. The period of the monostable is given by the formula T = 1.1 RC where T is the period in seconds, R the total resistance in ohms, and C the capacitance in farads.

Author :Daniel Lomitzky and Mikolajczak Tyrone  Copyright :Electro

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An Accurate Reaction Timer Circuit

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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Digital Stop Watch Using NE555 Timer IC

This is s design of digital stop watch circuit that built around timer IC LM555 and 4-digit counter IC MM74C926 with multiplexed 7-segment LED display. This is the figure of the circuit.


MM74C926 consists of a 4-digit counter, an internal output latch, NPN output sourcing drivers for common cathode, 7-segment display and an internal multiplexing circuitry with four multiplexing outputs. The counter advances on negative edge of the clock. The clock is generated by timer IC LM555. The circuit works off a 5V power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in a metal box with provisions for four 7-segment displays, rotary switch S1, start/stop switch S2 and reset switch S3.

For operation this circuit is explanation in the next. First, reset the circuit by pressing S3 so that the display shows ‘0000.’ Now open switch S2 for the stop watch to start counting the time. If you want to stop the clock, close S2. Rotary switch S1 is used to select the different time periods at the output of the unstable multi vibrator (IC1). This circuit is powered by 5V DC. That power supply can take from regulator power supply. You can read in this site about the regulator that can be used.

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