Timer Circuits

This circuit uses a simple 4060 IC oscillator/timer that is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state. The time can easily be set from seconds to hours...

A 555 timer generates a PWM drive signal to a power FET. Bootstrapping the entire control circuit across the FET using D1 allows an n-channel FET to make two-wire operation possible. Operating the PWM at a low switching frequency of about 120 Hz and shaping the rise and fall time minimize EMI without using any filter components. The optional components in the dotted box add short-circuit protection and may be unnecessary in many applications. You should size the FET`s on-resistance to the load (potentially saving some cost), but make sure the FET can handle the lamp`s start-up current, which is typically 10 times the steady-state current...

Figure 1 shows the classic way to use a backlight-driver IC to provide dimming. By modulating an external PWM signal, the circuit controls the white-LED current. By adjusting the on/off-time ratio, or duty cycle, the circuit can provide drive ranging anywhere from full-on to full-off. This circuit relies on the fact that the baseband or application processor has a PWM timer available. A second method of obtaining dimming is to use an adjustable analog-input interface (Figure 2). The drawback of this approach is that it requires a DAC block in the digital-baseband or application processor...

The 555 timer "light dimmer" schematic circuit is shown in figure 1 below. For the light dimmer to work the 555 timer is configured as a "variable cycle", astable oscillator running some where around 300 Hz. The power mosfet used here would be a TO-220 type such as MTP3055E or similar. Note the need for a TO-220 type heat sink for full rated loads...

Typically applications having LEDs and keypads also keep track of real-time, in order to synchronize certain related events. An Industrial Clock/Timer example has been used in this application note as a demonstration of these functions. The software overhead to keep track of real time is minimal and the user can modify the code to significantly expand the functionality of this circuit...

The Link telephone intercom is designed around two ICs. The first, IC1, is an NE 556 dual timer chip, which is wired up to provide dial tone, ring tone (busy tone too, which will be explained along with a few add-ons to be mentioned later on) and ring pulses for the ringer circuit attached to each line circuit. The other chip, IC 2, is a CD 4017B decade counter, which is wired to count each train of dial pulses as they are received and buffered by the two opto-couplers, OC1 and OC 2 and their associated R/C networks...

The circuit comprises a timer IC, two decade counters and a display driver along with a 7-segment display. The game is simple. As stated above, it is a scoring game and the competitor who scores 100 points rapidly (in short steps) is the winner. For scoring, one has the option of pressing either switch S2 or S3. Switch S2, when pressed, makes the counter count in the forward direction, while switch S3 helps to count downwards...

You can play this game alone or with your friends. The circuit comprises a timer IC, two decade counters and a display driver along with a 7-segment display. The game is simple. As stated above, it is a scoring game and the competitor who scores 100 points rapidly (in short steps) is the winner. For scoring, one has the option of pressing either switch S2 or S3. Switch S2, when pressed, makes the counter count in the forward direction, while switch S3 helps to count downwards...

If you are interested in model aeroplanes and have the capital, a radio controlled electric park flyer is a must have. An RC aeroplane under 400 grams floats around like the rubber models of my youth and contact with the ground doesn`t seems to involve that sickening crunch that comes with larger models. Finding a deserted park in which to fly one (that propellor can still be dangerous) and waiting for a windless day isn`t always that easy but it sure beats driving an hour to a club field. Park flyers are definitely stress beaters and are also just plain fun..

Eight LED`s are used to indicate the pad currently selected. These LED`s are connected to a decade counter, which sequences the LED`s when it receives a clock pulse.Only one LED can be lit at a time from the decade counter, so although this circuit contains many LED`s only a small drain us placed on the battery. The clock pulse for the decade counter is generated by a 555 timer...

The drawings and photos below are for an operating incline railway that was built by the London Model Railroad Group for its `O` scale model railway club located at London, Ontario, Canada. This is a single car model loosely based on a double car incline that operated at Port Stanley, Ontario. The mechanism is driven by a geared slow speed motor and controlled by an electronic timer circuit. The car waits for a preset time at the top and bottom of the incline before being slowly lowered down or pulled up the track...

Figure 1 is the block diagram of an easily programmed, single-button combination lock. You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button. The circuit uses inexpensive CMOS logic. The retriggerable timer, T1, locks out entries made after the T1 code-entry window, thereby greatly enhancing security...

Typical circuit representative of those used in most light switch type digital timers. The timer module is normally a PIC or custom chip, and it syncs to the AC line so that a trigger pulse can be supplied at the right moment...

This Design Idea offers a solution to the challenge of turning devices on or off in the past. In Figure 1, IC2 is a 555-type timer (preferably CMOS) connected as a monostable one-shot multivibrator. The pushbutton switch, S1, triggers IC2. You can replace S1 with a transistor or an optocoupler, for example. You can connect VOUT to a relay or a transistor, if needed. You might need to adjust the values of R4 and R5, depending on the output load and the characteristics of S1...

This is a circuit that could be used as a doorbell system like those that most homes have. From what I can tell, pressing the switch triggers the IC to oscillate and send electricity through the transistors to power the speaker. The IC type is not listed, but I am guessing that it is a 555 Timer...