Is there another, better way of doing this? (simple circuit diagram)

In summary, the conversation discusses the need for a small input to switch on a slightly larger circuit permanently, with the option to cut the power off or open the switch. The use of relays is considered expensive and not necessary for the desired voltage and current. Alternatives such as using transistors or physical switches are suggested. The conversation also touches on the topic of using a circuit to trigger the switch and the components needed for it. Finally, a resource is recommended for various circuit designs that could fulfill the desired function.
  • #1
wannab
32
1
K4pwP67.jpg


I need one small input to switch on a slightly larger circuit permanently, until I cut the power off or until I open the switch. Relays seem a bit expensive and intended for higher voltage applications than I require. Is there a way to swap the relay here with transistors or something?
 
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  • #2
Depends on how you want to control the switch and under what circumstances.
i.e. you could short-circuit the main one with a wire, and put a small explosive charge (like a firecracker) under the wire. Use a NiCad element to light the fuse.

You could use a knife-switch and a servo.

Since this is to be a "once on always on" device...
You could use a mousetrap as a spring-loaded knife-switch, held open by a bit of fuse wire - blow the fuse and close the switch. (There's a lot you can do with spring-loaded switches.)

But what you do depends on the circumstances.
 
  • #3
Simon Bridge said:
Depends on how you want to control the switch and under what circumstances.
i.e. you could short-circuit the main one with a wire, and put a small explosive charge (like a firecracker) under the wire. Use a NiCad element to light the fuse.

You could use a knife-switch and a servo.

Since this is to be a "once on always on" device...
You could use a mousetrap as a spring-loaded knife-switch, held open by a bit of fuse wire - blow the fuse and close the switch. (There's a lot you can do with spring-loaded switches.)

But what you do depends on the circumstances.
Sounds like I'll constantly need to replace components which isn't really what I want. I just want the switch to flick when there's a current so that the lamp and the buzzer stay on until someone deals with it.
 
  • #4
Ah - so you need to be able to switch it off as well.
That's not what "permanent" means.

There are any number of switching circuits ... depends how it is to be triggered.
Something provides a current when the lamp needs to glow? Presumably not enough current to light the lamp by itself - hence the relay.

What's wrong with just using a transistor?
Something more robust: trip a physical switch with a servo or a solenoid.
 
  • #5
wannab said:
K4pwP67.jpg


I need one small input to switch on a slightly larger circuit permanently, until I cut the power off or until I open the switch. Relays seem a bit expensive and intended for higher voltage applications than I require. Is there a way to swap the relay here with transistors or something?

What is your voltage?
How much current do you want to control?
How much is too expensive?

Could you please explain your symbols?
Is the inductor in the collector line supposed to be the coil of the relay?
If so, what does B represent in the switched circuit?
What does the symbol of the circle with the X in it represent?
Why do you have a resistor in the emitter line and what is its approximate value?
 
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  • #6
Simon Bridge said:
Ah - so you need to be able to switch it off as well.
That's not what "permanent" means.

There are any number of switching circuits ... depends how it is to be triggered.
Something provides a current when the lamp needs to glow? Presumably not enough current to light the lamp by itself - hence the relay.

What's wrong with just using a transistor?
Something more robust: trip a physical switch with a servo or a solenoid.
The problem with a transistor is that it only provides current while it has inputs, afaik you can't arrange them so that an impulse causes a permanent flow of current. Or am I wrong?
 
  • #7
skeptic2 said:
What is your voltage?
Very small, 6V or something. I haven't bought components yet.
How much current do you want to control?
Not very much. Just enough to light a LED and sound a buzzer.
How much is too expensive?
Well a relay is around £5 on eBay and I thought that was too much. It was also much larger than I expected for such a simple device. If there's a way to do it with transistors that'd be great.

Could you please explain your symbols?
X is a lamp, B is a buzzer.
Is the inductor in the collector line supposed to be the coil of the relay?
Yes.
Why do you have a resistor in the emitter line and what is its approximate value?
I'm not sure if it's completely accurate. I thought if I didn't then it would be a short.
 
  • #8
There's a 12V and 40amp relay on eBay for £2. Does this only work for around these levels or would a small current and slight smaller voltage work?
 
  • #9
Here's a chapter about http://openbookproject.net/electricCircuits/Semi/SEMI_7.html with several ways to do what you want.
e.g.

http://openbookproject.net/electricCircuits/Semi/03208.png [Broken]

http://openbookproject.net/electricCircuits/Semi/03320.png [Broken]
 
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  • #10
dlgoff said:
Here's a chapter about http://openbookproject.net/electricCircuits/Semi/SEMI_7.html with several ways to do what you want.
e.g.

http://openbookproject.net/electricCircuits/Semi/03208.png [Broken]

http://openbookproject.net/electricCircuits/Semi/03320.png [Broken]
Thanks a lot.
 
Last edited by a moderator:
  • #11


You're welcome.
 
  • #12


If you decide to go with the SCR circuit which I recommend, I'd also recommend that you put your LED (with the proper current limiting resistor) and the buzzer in parallel. In series, when the buzzer opens, the SCR will turn off.
 

1. How do I know if there is a better way to construct a simple circuit?

There are a few factors to consider when determining if there is a better way to construct a simple circuit. First, you should assess the efficiency and effectiveness of the current circuit design. Is it achieving the desired outcome without any major issues? Additionally, you can research and compare similar circuits to see if there are any improvements or modifications that could be made. Consulting with other experts in the field can also provide valuable insights.

2. What are some common mistakes to avoid when designing a simple circuit?

One of the most common mistakes in designing a simple circuit is not considering the power supply. It is important to ensure that the power supply is compatible with the components being used and can provide the necessary voltage and current. Another mistake is not properly grounding the circuit, which can cause interference and malfunctioning. It is also important to use the correct components for the circuit and to follow proper wiring techniques.

3. Can I use different components to improve my simple circuit?

Yes, you can use different components to potentially improve your simple circuit. For example, using higher quality or more efficient components can improve the overall performance of the circuit. However, it is important to ensure that the new components are compatible with the rest of the circuit and do not cause any issues.

4. What tools or software can help me design a better simple circuit?

There are various tools and software available to assist in designing a better simple circuit. Some popular options include circuit simulation software, circuit design software, and online circuit calculators. These tools can help you test and optimize your circuit design before physically constructing it.

5. Are there any resources available to learn more about designing simple circuits?

Yes, there are many resources available to learn more about designing simple circuits. You can consult textbooks, online tutorials, and instructional videos. Additionally, joining online forums or attending workshops and conferences can also provide valuable insights and learning opportunities.

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