simple momentary switch

[EXH01]

I’m looking to create a very simple mechanical momentary switch for a project which will change tracks on an mp3 player. The switch will need to be activated somehow by a slowly rotating shaft. I thought I had the answer by using a reed switch and magnets, but the resulting on/off from the reed switch was too slow as the magnets passed by, and doesn’t trip the mp3 player… it needs to be quick momentary switch. Additionally, the player will not tolerate any current flowing through the switch. The momentary switch will need to be something that can be tripped with very little resistance. I have experimented with LED detectors, and Hall Effect sensors, but both had current flowing through them which hung up the mp3 player. Whatever design I end up using, will need to be able to be reproduced easily and inexpensively. I am a novice with electrical circuits, but have access to people to help. Would appreciate any thoughts.

 

[tunedwolf]

The least resistance, mechanically speaking, would be the LED detection approach that you already tried. Just how fancy a control are you trying to build? You could, for example, want the Rolls Royce approach and have an encoder wheel on the shaft. By counting pulses using a slotted LED/ detector and maybe a small microcontroller, you could set the trip point anywhere around the shaft and output that to an analog switch. So changing the firing angle would be a simple code update. You could even get fancy and add a countdown to next mp3 track and output that on an LED status display etc. Or, you could just buffer the output of a slotted LED/ detector with a schmitt trigger and use that to fire an analog switch. Something like a 4066 or perhaps one of the fast 74AC series devices should do you. You could also delay from the trigger point using something like a 555 timer to fire your analog switch. It really all depends on your aspirations

 

[EXH01]

Thanks, Tunedwolf, for your quick response. Would like the switch to be very simple. I should have mentioned that the switch needs to be on demand. The shaft will be turned by human interaction, like someone dialing a radio, so a timed switch won't work, although the slotted LED is an approach I was trying to make work. Could I just use resisters to eliminate the current from the LED detector before it hits the player?

 

[alec_t]

Welcome to the forum!

Additionally, the player will not tolerate any current flowing through the switch.

That's not possible. There must be a small current. If you have an optical sensor then yes, a resistor can be used to limit current.

 

[Reloadron]

If you have a voltmeter measure across the switch and see what exactly is being switched?

Ron

 

[cowboybob]

I realize that you wish to keep your external switching circuit simple, but...

My experience with the external switching on many different MP3 players is that they are extremely sensitive to bounce. Such as what you'd get from a reed switch or any other mechanical switch. The bounce almost always caused the player(s) to hang.

And alec_t is correct, there is a current (very small) flowing in the MP3 switch(s). It is nothing more that an input to the MP3 uC chip that is, ordinarily, held in a HIGH state (as are the other control buttons). But this can be used to your advantage.

The only method for an external switching device, such as you propose, that I got to repeatedly work correctly, was a mechanical switch used to trigger a dual 555 cascade timer that then drove a simple 2n2222 transistor switch with its collector-emitter tied across the MP3 switch (thus isolating the MP3 from the 555 ckt. power): a bounce-less, finger press emulator, if you will.

You have to get rid of the bounce.

 

[EXH01]

Thank you cowboybob. Appreciate the insight and suggestion! Will work with collegues on becoming bounceless.

 

[KeepItSimpleStupid]

I've had great success using FET optocouplers to interface with buttons. The VTL51 has leads. The switches are usually part of a matrix. I agree with bob -- eliminate the bounce. High resisance like 200 ohms isnt usually a problem. Bounce is!

 

[KeepItSimpleStupid]

If the FET optocoupler wont work, an OPTOMOS relay should.

Your stick might interface better with a slotted optocupler or encoder. elmmelectronics makes some out of the box debouncers.