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Wireless circuit diagram needed for an Electromagnet.

Hey guys, i urgently need to build a wireless circuit using a simple on/off electromagnetic circuit that would drop a metal object when the circuit is switched off. i have a 12V dc powered electromagnet as well as RF receiver and transmitter pair. the receiver needs to be fitted with the electromagnet and i would be using 4.5v dc power supply for the receiver using 3x1.5V button cells.
Kindly help me with circuit diagrams and/or a list of other components such as generic IC/ timer 555/ resistors, capacitors, etc. which would be needed for me to build the circuit.
Thanks a lot.

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I drew you a diagram of maybe one way to do this. Let me know if the attached diagram makes sense to you. Here I am assuming the output on the receiver goes high, when the button is pressed, low otherwise.
https://www.instructables.com/files/orig/FRQ/T3DE/GVZPH7SH/FRQT3DEGVZPH7SH.jpg
circuit-electromagnet-dropper-thingy.jpg
him1703 (author)  Jack A Lopez5 years ago
the circuit makes complete sense. thank you.
just needed to ask 1 thing. i have been reading a lot online about how to go about doing this and at many places it is mentioned that we cannot simply connect a RF receiver to a circuit and expect it to send signals. We need to connect it to a Generic IC. Is that true? coz Rx Tx transmission consists of digital binary signals (1 and 0) and these digital signals need to be converted to analogue before going further or else the circuit wouldn't work. Is that true?
I dunno. Do you have a link to the data sheet for this receiver-transmitter pair? Or failing that, a link to where you got it from?
him1703 (author)  Jack A Lopez5 years ago
http://www.maplin.co.uk/media/pdfs/a59jn%20Datasheet.pdf
Wow! Those transmitter and receiver modules are much more complicated than I expected!
Each one wants a microcontroller driving it, and each one needs to be initialized, and wow! So making these work is a project that involves microcontrollers and programming...

You said that a circuit was needed for these "urgently". I think it would take me a month to figure this out. For someone talented who knew what he or she was doing, maybe a day or two, but that someone is not me.

If there's a deadline, I suggest finding an easier-to-use transmitter -receiver pair. For example, I think one of those found in a wireless doorbell would work. That's assuming you can find one of those locally.
him1703 (author)  Jack A Lopez5 years ago
thanks for the reply. i didn't know it would get so complicated. here are a few more links for another rx tx pairs. im guessing they would need micro controllers too but please have a look and let me know.

http://www.farnell.com/datasheets/34489.pdf

http://www.maplin.co.uk/media/pdfs/vy48.pdf

http://www.farnell.com/datasheets/621935.pdf

other than this i was thinking that only achieving the code for the IC programming is an issue. time on the other hand isn't that big an issue. i start building the circuit on the 10th of January. until then its only the circuit design i needed which can be changed later as per requirements. even if i get the programming done by the end of January it'll be fine.

but what if i use IR wireless components instead of RF? would that make the circuit easier to build and would the circuit be similar to what you designed?

also, in the circuit diagram that you made, where exactly would the micro controller fit in? would anything else change in the circuit or just a simple addition of an IC chip?
Those, most recent datasheets you linked to, look like they could be used without a microprocessor. However, I'm still going to recommend getting a wireless doorbell and hacking that, just because it will probably be easier to start with something you know works, and then sort of modify it from there.

Regarding the use of IR, that will work too, if you've got line of site between the transmitter and receiver.  For example, this page:
http://www.bowdenshobbycircuits.info/irswitch.htm
shows how to make a switch activated by any IR remote (e.g. one for an old TV).   Also this instructable:
https://www.instructables.com/id/Turn-any-IR-remote-control-to-a-wireless-control-O/

At the heart (or maybe the eye?) of those projects is a little IR receiver module, and what that does is detect the presence of  40-KHz modulated IR, and then output O or 5V, in the form of fast pulses.  It's easy to make a circuit that simply turns on when (almost) any IR remote is pointed at it with button pressed.  The task of decoding the little pulses, and figuring out exactly which button was pressed, is more complicated, but   presumably you don't need to do that.

Anyway, this question of how to make a simple remote control of some kind, it gets asked in this forum a lot.  It's a shame there aren't more good, clear, instructables on this subject. 

BTW, there are also a few 'ibles here that involve hacking a wireless doorbell, but it seemed to me that most of them were not all that lucid.  Of course you can seek these out yourself, using that  "search" wigit at the top of the page there.

him1703 (author)  Jack A Lopez5 years ago
thanks a ton for your help. ill try working with a wireless doorbell circuit or IR switching circuit. will post again if anything fruitful happens.
Is your reciever designed such that it produces an output voltage that is on (high) when it is receiving a signal but then turns off (low) when the RF signal is not present? This would be common for many off the shelf TX/RX module pairs.

If that is the case, then the output from the receiver could turn on a transistor (FET or BJT), which in turn lets current flow through the electromagnet and keeps the object held in place. When the transmitter signal is no longer receiver, the receiver output goes low, the transistor turns off, and the object is released.

In such a case the only extra parts you would need would be a transistor that can handle the electromagnet current and a diode to prevent damage to the transistor when the electromagnet is turned off, plus a couple resistors.

One problem I see is if you plan to power the electromagnet from the button cells. You don't say how large your electromagnet is, but unless it is pretty small your cells would go dead quickly if it has to hold the object up very long.
him1703 (author)  LargeMouthBass5 years ago
thanks for the quick reply. i am using a store bought rx/tx module pair so i'm almost sure it would work the way you mentioned it would.

also, i need to run the electromagnet for one and a half minutes max. i forgot to mention though that i plan to use different power supplies for the electromagnet and for the receiver. for the receiver i'd be using the button cells whereas for the electromagnet i will be using a 12V A23 battery (used in cameras). there is a weight limit i need to follow so i cannot go for a heavier power supply and the A23 battery would be sufficient to run for one and a half minutes imo.

which brings me to the next question. is it feasible to use two separate power supplies in the same circuit? also you mentioned i would need a couple of resistors. how should i calculate the amount of resistance needed in the circuit?

this is my first time i'm building a circuit on my own so i'm finding it a bit tricky. i'll probably post a conceptual circuit diagram soon that gives a basic idea. thanks.