Easyvibe Rate LED

[Torchy]

I've searched all the easyvibe posts but no-one seems to have worked out how to get a panel mounted LED to flash with the rate setting.

On the univibe (ie bulb) circuit the LED option is easy but the biasing on the easyvibe looks like another LED would take the lfo down.

Anyone done this ?

[BDuguay]

There is a 220 or 240 ohm resistor feeding the leds. Tap off of that to your status led. I found you needed another led in series with your status led to achieve the proper visual effect.
This worked for me but there could be other ways.
Anyone else care to chime in?
B.

[MarkB]

I tried that.. the voltage drop was too much, I think.. it killed the LFO - so I just have a normal LED right now.
"-)

[BDuguay]

If you tap in before that resistor it doesn't effect the LFO.
At least that was my experience....

[MarkB]

hmm - I'm pretty sure I tapped it before the resistor (after the trimpot) and it still gave me a flashing status LED, but no LFO.

Of course - if I wired the other end of the status LED to somplace OTHER than the other end of the LED/LFO chain for ground - would that tap off all the voltage and kill the LED?

Do I have to take the + from after the trimpot and wire the - to the - of the last of the 4 on-board LEDs?
"-)

[R.G.]

OK, guys, let's take this logically.

(1) You want to have an LED that flashes in synchronism with the LFO.
(2) You don't want to affect the LFO

(1) says that you have to get the voltage to a range that makes an LED dim and brighten. (2) says that you have to either have a rough, tough burly LFO that doesn't mind the extra LED current, or you have to put in enough buffering so that the loading on the LFO isn't a factor.

On the EasyVibe, the LFO already drives LEDs, so the voltage is close anyway. You will probably need to buffer the LFO voltage, and the easiest simple buffer is a high gain NPN transistor. So - using Keen's Second Law - we pick a 2N5088, hook its collector to +9 (gotta get power from somewhere) its base to the LFO voltage, and its emitter to a resistor in series with the flashing LED to ground.

Oh - you wanted it to go off when the effect is bypassed?

You have two options. You can kill the LFO when the effect is off, or you can use a second NPN transistor to switch off just the indicator LED. That's another 2N5088 with  collector-emitter inserted between the LED and ground, and a resistor on its base to limit base current tied to... what?

You need a signal that goes high when the effect is switched on. You can do this with either a 3PDT switch or a Millenium Bypass. Both provide a high signal when the effect is on. You just take out the LED from either, and connect that signal to the base of the ground-switch transistor. You may have to use a resistor to ground on the switch/Millenium to keep leakages from turning on the super-sensitive 2N5088.

Done.

On pedals where the voltage is not suitable for LEDs directly, you will need increase the voltage level (such as in MXR P90-esque things) by using an opamp follower with gain to boost the signal up. For pedals where the signal is 'way big, you use a resistor divider to divide it down, or a bigger resistor in series with the LED to cut the current down.

[MarkB]

..and once again, one of the great minds of this forum puts it in a way that I can easily understand.

thanks, RG - I think I get it now.
"-)

[RDV]

Personally, I would want the LED flashing all the time so I could set up the speed with the effect bypassed, like I have on my EA tremolo. However; my PCB and wires are a little dainty(telephone wire, and one pad has already raised on the PCB and had to be superglued back down), so I'm probably done with the mods(took input cap up to .1uF, worked well). I've got to take the plunge & start doing my own PCBs.

Regards

RDV

[Torchy]

Thanks to everyone who contributed especially RG ... going to try the transistor mod asap

A trick I saw somewhere else was to connect the panel-rate led in parallel with the lfo leds but reversed polarity so the supply to the rate led is sunk thru the op-amp rather than sourced from it .... hmmmm gotta try these things anyway  :wink:

[R.G.]

A trick I saw somewhere else was to connect the panel-rate led in parallel with the lfo leds but reversed polarity so the supply to the rate led is sunk thru the op-amp rather than sourced from it

It can be done that way. You have to either leave it on all the time (which some people like, some don't) or you have to then use a PNP turn-off transistor and a negative-going turn-on signal to the PNP base.

There are a lot of variations. All of them just couple the LFO to an LED in a way that's buffered enough to drive the LED without loading down the LFO. Anything that does that works.