Using a 5v relay as a momentary switch

[Enzo]

I'm not suggesting to drop the relay, just controlling it with something other than a pressure switch.


May I assume you have addressed positioning of such a switch? I'd imagine directly over the pivot shaft? I'd hate to find that a toe or heel position might react to reduced pressure when the pedal is at the other extreme and drop out the relay and so the effect goes off.

I had a guy complain his wah sswitch was too stiff, he had to push hard with his toe to turn it on. SO we lightened up the switch action. Then he brought it back not long after. It seemed that when wah-ing actively, a lot of time pushing the pedal down clicked off his new light-action switch.

[Bloodbath]

Enzo, I understand and thank you for the suggestion of not using a pressure switch. The more I think about it, your right, it just isn't a good idea. I have wired up a wah for him using a dpdt momentary switch that I mounted on the treadle right where the ball of your foot would be and that seemed to have worked perfect. There isn't a problem with losing contact. The problem was the switch actuator is plastic and breaks off pretty easily. I'm going to try and use a tactile switch with an actuator that is just tall enough to barely stick out of the rubber pad. I realize I'm still dealing with plastic but I think it will last longer.

[Enzo]

There are fancy volume pedals - expression pedals if you prefer - for organs and other things, and they have little vertical "wings" (I don't know what else to call them, like the little vertical tips on modern jet liners wings) sticking up from either side of the main pedal. They activate microswitches to enable some feature, like note bending. For the life of me I can't think of a name example to link to. You turn your foot slightly to the side to activate.

Back to your idea.

Look at a microswitch, or what I call a microswitch. One of these things:
SPDT Snap-Action Standard Micro Switch with Offset Lever 060-604

The metal blade is actually an option, you can order them with or without, and some metal blade ones even had a roller on the end. Point is that the little platic tit that activates the switch is not touched by the outside world. That springy metal strip, probably phosphor brinze or some such, presses down on the switch. The lever action amplifies the pressure, so very little pressure is required, but it also takes direct contact away from the plastic tit. You might adapt that sort of idea. I have springy strips from my days in coin-op amusements. Pinball machines were just full of them, and most of the shoot buttons on an arcade video game used them until they all wen't to microswitches. But I bet a hobby store or metal shop might have something. Or just get a microswitch.

[Bloodbath]

Thanks Enzo. I was actually just looking at those lever switches. I got the relays today and the ones I ordered "turn on" at about 5v and they all go back to "normal" when I remove the voltage. This is going to work perfect. I'll only have to run power outside the pedal to whatever switch I use so that's a lot less wires than having a dpdt outside.
For the switch I was actually thinking a tactile switch with a really long actuator might be good. I could mount it under the treadle on a little circuit board and only have to drill a hole for the long actuator to stick up through the treadle and rubber pad. I could even put screws under the rubber sticking down under the treadle so the switch height could be adjusted.
I may try this route and if it isn't so good, I may try a lever switch.
Thank you guys so much for all the ideas and help. I'll let you know how it goes and I'm still open for other suggestions so keep them coming!!!!!!

Edit: What I like about the tactile switch is the fact it takes very little pressure to activate it but on the downside it takes very little pressure release to deactivate it. I think how much it sticks up and if I can find one that has a longer distance between on and off is going to be the key.

I do have a question. Since I'm just using the relay as a momentary switch, do I need any other components to make it work safer, longer, more stable, or anything? Should I put a diode across the coil?

[Enzo]

They call the microswitch I linked a "snap action" switch. It has some hysteresis - you push it down so far to activate it, but it deactivates higher up than that. In other words there is not one point right on the edge wher it teeters. The wall switch in your bedroom is probably like that. FLip it 60-70% up to turn on, but doesn;t turn off until you push it 60-70% down. I hope I am describing this clearly. Hence snap action. That sort of switch eliminates the unwanted right back off again thing. Also, just as tactile switches come in a variety of actuation forces, so too do snap action switches. Some are extremely light touch, and if you have a lever operating them, even less force.

Your relay coil merely needs current to operate, but it is a coil of wire - an inductor. When you turn off the current, that inductor generates a spike. And that spike right near your signal path could be picked up as a pop. Look at the channel switching relays in any guitar amp, and you will see a diode across the relay coil wired reverse bias. That way the main power supply does not flow through the diode, but when the current is removed, that diode clamps off that spike.

That little relay's spike probably won't hurt your switch, but the inductive spike on a heavier unit coulod arc switch contacts, or if driven by a transistor, the spike can kill the transistor.

[Bloodbath]

I actually have a few of the snap action switches I've pulled from things over the years. I'll have to give one a try to see how it works out.
I think I'll put a diode across it no matter what. Couldn't hurt and it's only a couple cents. I'm thinking a 1N4148 would be suitable enough in this case? So the negative of the diode goes on the + of the relay correct?

[Enzo]

I don't think in terms of positive and negative on a diode. The cathode would go to the +5 end. Just think of how you'd wire the diode so it did NOT conduct the +5 to ground.

[Bloodbath]

Thank you. Do you think a 9v relay should have a resistor or something on the V+ just to drop it down a little since a fresh 9v battery or a 9v power supply is typically over 9v?

[Enzo]

Beats me, find out.

[Steve Conner]

No... The relay won't care a couple of volts either way. Also, a fresh 9v battery won't be fresh for long if it's powering a relay, and a 9v power supply should be almost exactly 9v.

[Bloodbath]

Ahem... Hey Blood, I myself am not happy wanting foot pressure on a unit that requires also foot motion. COnsider an optocoupler? Mount an LED off of one side, and a photocell on the other. Then a basic circuit would detect the presence of a foot blocking the light, and control your relay or whatever.

Just wanted to follow up on how this project is going.
I actually went with Enzo's LED/LDR idea. It's working really well. I have a little darkness detecting circuit that is working really well. It has a sensitivity pot to adjust for different lighting conditions. I bought a bunch of different LDR's and tried them all out to see what would work the best. I can still hook up a spst to it if I need to also. Maybe a switch to switch between the spst and LED/LDR?

[Bjarneec]

Sorry for using this, but Think you Can answer
I need an relay or something that Can do the following:
I am building an race simulator and am building an button box With momentary -normally/open switches as they replaced the keyboard buttons. I wired the button from an old joypad. BUT i really needs an flashing LED to blink when the button is pressed, but as it is a momentary the LED Will just stop blinking when its released again. It need to stop blinking when pushing the switch 2. Time. (I need it for speed limiter). What do I need?the joypad is connnected to usb so it must be 5v.

Thanks in advance