So I am just a mechanical engineering student and I am working on a personal project to learn more about circuits and how they work. I really don't know much about this stuff so any help would be great. What I am attempting to find is some type of time delay relay. What I need is a relay that has a 5-12v DC input and is normally closed. So when the voltage is supplied, it would be passing current straight through to energizing node 1. I would like to have a trigger(node 3) apply a low voltage with very low current(maybe 50 milliamps) to the relay and switch the relay from node 1 to node 2. Now the trigger would only be energized for a short time, but I would like the relay to stay switched to node 2 for around 5-10 seconds. Is this possible? Does a simple, inexpensive unit like this exist? I obviously don't know much so simple answers would help a lot! Thanks in advance!
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Hi mav76 and welcome to the Electronics Point forums 
You have a positive DC voltage in the range 5~12V that enters your relay on a "common" contact. Initially and normally, the relay will pass this voltage to a terminal called "1", but it can be temporarily switched to a terminal called "2".
You have a control input, called "3". You will apply some kind of signal to this input for a short time, and each time this signal appears, you want the relay to switch from terminal 1 to terminal 2 for a fixed period of time, around 5~10 seconds, then return to terminal 1.
What is the nature of the signal you will be providing to the control input? Is it a positive voltage? If so, what voltage? Or is it a connection to the 0V (ground) rail?
Assuming you want to use an electromechanical relay, you really need to decide on a supply voltage. Relays are available with 5V or 12V coils but the range 5~12V is too wide to support, unless the circuit includes a regulator, which complicates things somewhat.
Can you tell us what this relay will be used for? This will help us to be confident that what we suggest will do the job you intend it for, and it might help us suggest different options that you may not know about.
In other words, please start by explaining your whole project from the beginning. This will enable us to suggest the most appropriate solution.
OK, let me clarify your requirements.
You have a positive DC voltage in the range 5~12V that enters your relay on a "common" contact. Initially and normally, the relay will pass this voltage to a terminal called "1", but it can be temporarily switched to a terminal called "2".
You have a control input, called "3". You will apply some kind of signal to this input for a short time, and each time this signal appears, you want the relay to switch from terminal 1 to terminal 2 for a fixed period of time, around 5~10 seconds, then return to terminal 1.
What is the nature of the signal you will be providing to the control input? Is it a positive voltage? If so, what voltage? Or is it a connection to the 0V (ground) rail?
Assuming you want to use an electromechanical relay, you really need to decide on a supply voltage. Relays are available with 5V or 12V coils but the range 5~12V is too wide to support, unless the circuit includes a regulator, which complicates things somewhat.
Can you tell us what this relay will be used for? This will help us to be confident that what we suggest will do the job you intend it for, and it might help us suggest different options that you may not know about.
In other words, please start by explaining your whole project from the beginning. This will enable us to suggest the most appropriate solution.
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