In this post we learn a simple IC 555 set/reset application circuit for activating or deactivating a relay alternately.
Circuit Description
This electronic set reset circuit is very simple, easy to implement and very useful.
It can provide you many applications options in cases where it may be necessary to toggle (switch on and off) any electrical or electronic device
Understanding the ON-OFF or set/reset operation of the timer switch 555
To operate the timer 555. In this popular integrated circuit there a relay is connected via a BJT with the intention of connecting or disconnecting of the device to be controlled.
Manual activation may be performed via two momentary push ON switches. One serves to activate the device under control and the other for deactivating the same.
When the circuit is operating, activation of switch 1 (SW1) enables the pin2 of 555 linked to 12 volts normally, pulling it to 0 volts such that the timer output (pin3) is activated, allowing voltage 12 volts here. Thus, high output activates the relay 555 through the transistor Q1 (which saturates)
For disabling the relay, simply switch 2 (SW2) is pressed.
This puts pin 6 of timer 555, at a high voltage temporarily. The output of 555 that is pin3 now gets a low voltage level at its output, deactivating the transistor in the course, and clearing of the relay.
Circuit Schematic
Note: In the explanation of the circuit, it is proposed to be fed with 12 volts, however it may work well even with a voltage range from 5-15 volts. One can use a 9 volt battery PP3, and thus have a much portable circuit.
IC 555 pinout
List of circuit components for the above explained IC 555 set reset circuit
- Resistors: R1 = R2 = 3.3M, R3 = 10K, R4 = 1K
- Capacitors: C1 = 10nF
- Transistor: BC547
- Rectifier Diode: 1N4148 or equivalent
- Diode LED: 1 red
- Integrated circuit: NE555
- Relay: 1 with identical voltage to the supply voltage of the circuit
- Switches: 2 momentary or similar push ON contact. (SW1, SW2)
- Other: battery connectors (CN3), switches (CN1, CN2). View the latest chart.
By: Manisha Patel
nitin chaudhari says
Hello sir,
Is there any cmos ic can be uset for set reset circuit with low power consumption than NE555 , so that can be used with battery with long life. Pls if possible publish a post with circuit.
Thanks in advance
Swag says
Hello Nitin, You can find many CMOS based circuits if you search it online, I presently do not have it in this website…however if reducing current consumption is your main requirement in that case you can also try a transistor based design, as discussed in the following example post
https://www.homemade-circuits.com/simple-gate-openclose-controller-circuit/
Geoff Nutley says
Hi Swagatam, Thank you for the confirmation, yes I have a diode on the relay coil. You are right about the quality of the IC's they are the "dodgy 10 for a dollar ones", I shall invest is some decent ones.
Thank you
Regards
Geoff
Swagatam says
you are welcome Geoff!!
Geoff Nutley says
Thanks Swagatam,
The basis of what I am trying to achieve is I need to hold a solenoid active for around 10 seconds,the trigger is a high. I tried a 555 monostable and got the time with capacitor and resistor values, but trigger for this is a low so I ran pin 2 through a BC547 to switch the signal to ground and send pin 3 high. This worked a few times and now pin 3 stays high all the time , I think it may be fried. The output of pin 3 goes through a BC547 a 12 volt relay to the solenoid. The solenoid is 12V 1A,the relay coil 50mA and I have 10K resistors on the BC547's. Do you think I am on the right track or is there a better way.
The trigger voltage is 5 volts.
Regards
Geoff
Swagatam says
Hi Geoff, you have done everything correct in your design.
Did you connect a diode across relay coil?
I cannot see anything wrong in your design, may be the IC itself is not a good quality one, you can try replacing the IC…or the BC547 could also be examined for the same.
Geoff Nutley says
Hi Swagatam, I was just wondering if I could ask you about a circuit that is based on the above circuit but has a different trigger requirement.
Regards
Geoff
Swagatam says
Hi Geoff, you can feel free to ask it.