Greetings - I have a lot of experience assembling circuits...just not designing them. I am looking for a circuit that will send a single pulse of 9-24vdc to a small electromagnet. I need the pulse to be faster than a momentary switch...thus the circuit. The circuit will eventually be triggered by remote control. I can do this with an arduino and relay, but there must be an easier, more compact way. Any help is appreciated.

 

You could use a DC supply and bridge rectifier followed by an SCR, the SCR can be triggered for as many of the 120hz pulses as you need, from a 555 etc

 

a small electromagnet

What is its inductance/resistance?

 

define "faster"...

 

I need the pulse to be faster than a momentary switch

So how will the pulse be triggered if not by a switch, as switches give a fast pulse.

 

What is its inductance/resistance?

It's about 7 ohms

 

define "faster"...

View attachment 316184

Why would two relays be used? This is a learning experience for me.

 

there is only one relay. its NC contact is in series with input and it will open when relay coil is energized (almost instantly). the inductor L is the load (electromagnet) that you are sending pulse to. this way you will get short pulse to electromagnet regardless of how long the button is pressed.

is this clearer?

 

here is another variant if the button cannot handle the load current.
it uses capacitor which also makes it possible to extend the pulse
if course the whole thing can be done without relay, just don't know what your comfort level is....

 

What sort of remote control are you going to use?

 

there is only one relay. its NC contact is in series with input and it will open when relay coil is energized (almost instantly). the inductor L is the load (electromagnet) that you are sending pulse to. this way you will get short pulse to electromagnet regardless of how long the button is pressed.

is this clearer?
View attachment 316187

Yes, thank you!

 

here is another variant if the button cannot handle the load current.
it uses capacitor which also makes it possible to extend the pulse
if course the whole thing can be done without relay, just don't know what your comfort level is....
View attachment 316188

Thanx. As long as I have a schematic, I can build almost anything.

 

What sort of remote control are you going to use?

433mhz...I am building special effects and use those for most of them.

 

If you are triggering remotely, why not generate the pulse with the microcontroller? If the shortest pulse you can produce in software is still too long, you can shorten it with something like this. Adjust R2 to change duration of the output pulse.

Keep in mind this is a barebones approach. The timing of this circuit is a function of a number of variables. For example, changing the GPIO voltage from 3.3V to 5V will increase the pulse duration so you'll have to adjust R2 accordingly.

 

Here is an improved version with shorter turn on and turn off times for the MOSFET. Now it's a nice square pulse. Minor adjustments to R4 change the output pulse duration.

 

A simple way that might work quite well, given that I do not know the required current or the coil resistance. The circuit in post #9 is what I recommend. But an alternative is to have the capacitor in series with the contact and the coil, so that the capacitor charge current will power the coil. You will probably need to experiment with the value of the capacitor to provide the function the magnet is supposed to provide. The series capacitor has worked well for a lot of folks. Yo may also need to add a high value resistor (47K ohms) across the capacitor if repeated operations over a short time are required.