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r/electronic_circuits•
AssCommander

simple 3 second push/hold to activate circuit?

How would I go about making an RC circuit that requires a push time of 3 seconds or so before it discharges and activates a relay?

Is it possible with just capacitors and resistors?

Furthermore, would two buttons work like i describe below?

Button A, would charge a capacitor after 3 seconds of holding (letting go of the button would discharge the cap, so like a reset, and holding too long would discharge and reset[but how?])

While Button B, simply sends the charge which activates the relay. The whole thing is that Button A cannot be held for a time >3< seconds.

Is there anything i'm not understanding correctly that makes this harder than it seems?

Posted Jul 24, 2017, 9:34 PM UTC · edited

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wwwredditcom•

Minimum 3 seconds is an RC delay circuit. Between 3-4 seconds requires an additional transistor at the cap output to discharge the cap rapidly (disable). Easier to implement using a microcontroller.

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Vaporware371•

Most relays have sort of a minimum voltage at which point they activate. You may be able to get something to work by setting up a basic RC circuit, charging a capacitor through a resistor, and then put your relay coil in parallel with the capacitor.

You'd push the button, and current will flow through the resistor. Some of this current will flow through the relay coil (but not enough to turn it on), while the rest will charge the capacitor. At some point, there will be enough voltage in the capacitor to switch on the relay.

The caveat? First, assuming your bike is a 12V electrical system, you're probably going to need a 5 or 6 volt relay, and set up your resistors like a voltage divider. Second, you'll need to measure the resistance of the relay coil, so you know how to set up your voltage divider in a way that gives good timing, but doesn't expose the relay to excessive voltage.

Once this is on, you'll need to think about how it stays on. There are self-latching relays, as well as "latch" circuits that use two relays in a sort of "push-on push-off" configuration. This way, you push the button for enough time, "arm" your bike, and start it up. You may also need some kind of circuit that senses the ignition or headlight has been turned off, so you don't kill your battery leaving these relays running.

I like doing relay-logic stuff, and for the type of circuit you're building, you can find some pretty small devices that won't consume a lot of power. You'll need maybe one at the output end, with a higher current rating, to drive the solenoid (some of these have driver circuits, some don't), but the rest can be pretty tiny. That being said, There's a point where it may be worthwhile to look into something like an Arduino, simply on the basis of conserving space and power, especially if you're trying to integrate some more complex logic like a code-lock.

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AssCommanderOP•

Cool, I really needed some kind of confirmation that the idea would work and could probably be tunable by different values on the resistor and capacitor, right?

I found a 12V 30A relay that got pulled out of a car at some point, and in tinkering with it I figured out the latching Circuit.

Basically pushbutton from trigger to power source, while the N.O contact leads back to the trigger. Am I missing anything with this? I'm planning to just flip the switches every time I shut down my bike for added effect on start up, Haha.

I thought about looking into IC chips, but I'm really into the idea of figuring this out from scratch.

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AssCommanderOP•

As for the code lock, I was thinking of just using three-way toggles straight across and having the wiring of one switch affect how the others should be positioned while having a master three-way that sets the "code circuit"

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AssCommanderOP•

I'm planning to use this in an overly complicated "anti-theft" electronics panel on my motorcycle, mostly for the novelty of course.

This relay activation circuit will trigger the relay which will be wired to stay activated and send voltage to a series of 6 toggles which when set in the correct position and order will then allow you to use the starter motor button and headlight toggle switch

the system is 12 volts of course, and there is a solenoid leading to the starter.

Do I have to worry about toggle switch powder ratings, or does the solenoid use a low current trigger?

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