Help building a momentary footswitch with a latching LED.

[Bourbon]

Greetings.  First post here. I read through the wiki and faq and tried searching, but I could not find exactly what I a looking for. Also, please be gentle. I am still tryingt o learn theory amd schematics. I have built one pedal from a kit and done some basic repairs and upgrades to guitars and basses. I am no expert.

I have a SWR bass amp with the Subwave effect on board. It , operates with a momentary switch. There is no indicator light on the footswitch. That is what i would like to change.

The switch is run through a mono cable which is carrying about 3.5 volts. I would like to add an LED that stays on when the momentary switch is pressed.

There is enough room in the pedal housing for a battery, if needed. I am also no opposed to wiring it to accept my 1spot plug.

Just for reference:  there is a momentary switch with a latching LED sold in the UK by Bright Onion (hopefully the name drop doesnt violate the solicitation part, if so, please delete that part) but it is 35£, pus shipping to the USA. I am sure I can build it locally for less!

Thanks in advance. I know its longwinded for a small project, but I figured more info is better than not enough!

[mykaitch]

The easiest way would be to add a battery and some kind of set-rest latch, a couple of 555s would do it, or maybe even one depending what the switch does. I suspect that when you press the switch the 3.5 goes to 0v (ground) but this is useful if it does. Also a couple of sub min relays would work but you would have to get some low current ones.

[Bourbon]

Thanks for the reply. Please correct me if I am wrong with what follows.

With the relay, i am assuming a low voltage relay (9v) would be best so i can use a 9v battery or wall plug. I will also assume that wiring a relay for this application would also use pins like an automotive relay? Ground, line, switched power, and the load?
When the momentary switch comes on and triggers the relay, will pressing it again deactivate the relay?

Edit: would using a SPDT momentary switch connected to the normally open and normally closed lugs on the relay work to activate/deactivate the relay?


Is there a schematic or diagram showing any of these setups?  
Also, forgive me, but what is set rest latch or a 555? Im a rookie, at best.

Thanks!

[mykaitch]

You would neeed two min relays. I will post a sketch ASAP and an idea of batt life.

[JFace]

If you got a double pole double throw momentary switch, you could wire one of the poles the way your current switch is wired. Use the other pole to operate a flip flop circuit (do a search for CMOS switching for various ways to change from high to low using a momentary switch). The 3.5V could potentially power the circuit, but I would breadboard it first just to be certain. If not, it would require a separate power supply. Another obstacle would be ensuring that the state on startup matches the state of the effect.

[JFace]

Or, you could tap into the flip flop logic going on inside of the effect, send that high/low signal on a third conductor using a stereo cable using stereo jacks, and use that feed to light an LED, with an appropriate current limiting resistor.

[GibsonGM]

BJT flip flop, like JFace said, or this (easy):  http://www.digikey.com/product-detail/en/EC2-12SNU/399-11030-5-ND/4291096

Nothing to bugger up, it's all solid-state, only $2.  I am using this instead of an H bridge for someone I'm helping with model train track switching. 

[Bourbon]

Wow, thanks for all of the input! It looks like the circuit might do the trick, and looks like what has been suggested. What do you all think?

http://www.sabrotone.com/?attachment_id=2416

[JFace]

Wow, thanks for all of the input! It looks like the circuit might do the trick, and looks like what has been suggested. What do you all think?

http://www.sabrotone.com/?attachment_id=2416

I've used that design and it works. Still you need to determine how to ensure the state of the effect can match the state of your LED on startup. Also you will likely need a separate power supply.

[Bourbon]

A separate power supply is no big deal. I have a 1spot i can use the daisy chain for. While doing some reading on the subject of the state on startup, i have read that unplugging the pedal amd hitting the switch on the amp and then reconnecting the switch has worked for some users. I will attempt this sometime in the next week and post my results.

[mykaitch]

I've drawn one up with a 555 and a FET. Very low current. Will post it.
I believe this chap just wants LED indication?
I am assuming that when the switch closes the 3v5 goes to ground.

[Bourbon]

Mykaitch, that is what I am looking for, and it does ground out.