How does circuit work

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Sequential Actuator for powering up to four devices

It is common that sometimes we need to power some devices ¤âuccessively one after the other. This function forces us to handle a large number of switches, which are located where the access is difficult, especially in the case of informational devices and their pipelines. This sequential actuator ensures by itself the activation of one to four devices in a specified order and a defined delay for each of them. In the same way, it turns off the devices in the reverse direction of the ones that triggered them in the same automatic mode.
Sequential Actuator for powering up to four devices - schematic

Sequential Actuator for powering up to four devices - img1

Sequential Actuator for powering up to four devices - img2

How does circuit work

There are many methods to construct this type of operation, but this circuit is simple and original. In fact, it does not use an internal clock system as expected, but an integrated circuit LM3914, which is designed to control the activation of 1 to 10 LEDs depending on its input voltage.

The LM3914, with the IC1 characteristic in Figure, measures the voltage displayed at the terminals of capacitor C2. This capacitor is slowly charged through resistor R2, once the switch S1 is switched off. From this, the outputs of the integrated IC1 pass at low potential one after the other according to the charge rate of capacitor C2. Instead of controlling a simple photodiode, its outputs act on the photodiodes contained in optically coupled TRIACs or static relays, if desired, TR1 as TR4, whose outputs can control up to 12A at 220V, if necessary.

Since switch S1 is in the off position, capacitor C2 is discharged via resistor R2 and the outputs of the integrated IC1 return to the high level, which in turn blocks TR4 as TR1. The total pause or activation time is set by the R2/C2 elements, which you can freely change according to your wishes. The power supply no need to be stabilized and can be left in a feed block whose output voltage is set to 9V.



Although it can control four devices, the printed circuit (PCB) is extremely compact. It should be noted that no space has been calculated for the TR1 to TR4 heatsinks. In fact, and for use in high-fidelity audio systems or for computer system installations, these components will control currents of 1A to 2A maximum. In this case they do not need any heat sinks. The components used do not pose any problems of finding, except for TR1 to TR4.

Construction will be done in the classic way. First passive components and then active components. The optocouplers TRI as TR4 will be connected in series with the network supply of the devices they will control. To simplify the wiring, a good solution is to place it in parallel on the power switches of these devices. In this way, in the switch-off position, the devices operate automatically and are driven by sequential activation, and if necessary, it is always possible to turn them on manually by switching the switch to the operating position.

Considering the presence of the grid voltage at the terminals TR1 to TR4, you should obviously take all the necessary precautions and the circuit will be placed in an insulated box or in a metal box that has been grounded.

With the R2 and C2 values, it takes about 7 seconds to switch between the sequential activations of the devices and about 15 seconds between successive device deactivations. If you think this is a long time, you can lower the value of R2 or C2 respectively. With a value of 10μF for capacitor C2 the time goes down in one second between each successive activation and about 1.5 to 2 seconds between each successive switch-off.


IC1: LM3914
TR1-TR4: S212S01 by SHARP
D1: 1N4004
R1: 4.7kΩ
R2: 470kΩ
R3: 1kΩ
C1: 470μF / 25V
C2: 100μF / 25V
S1: switch on / off
IC socket DIL18


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