Help with Battery indicator LED schematic

[Atodovax]

Hi everyone! Could someone help me understand how the LED Battery indicator of this schematic works? Somehow its not working on my build , hehe...

[Rob Strand]

I think R22 should got to ground not +VB.
(or at least be switched to ground.)

The design looks bad as there is no resistor limiting the LED current.

To be honest it looks like the battery detect circuit is drawn wrong.
Maybe the transistor pinout is wrong.

[Atodovax]

I think R22 should got to ground not +VB.
(or at least be switched to ground.)


The design looks bad as there is no resistors limiting the LED current.

To be honest it looks like the battery detect circuit is drawn wrong.
Maybe the transistor pinout is wrong.

Thanks Rob, i though the same about that resistor. I guess i will just omit this part and just put a Zenner in series with the LED. Do you know of any "common combination" of series Zenner + limiting resistor + LED. I was thinking, maybe 6.8 Zenner + 10k resistor + Red 3mm LED.

[Rob Strand]

Just copy of the Boss or Ibanez circuits.   Very basic circuit,  no need for a transistor.

+9V --- 3k9 resistor --- K [5.1V zener] A --- A [LED] K--- GND

You can tweak the brightness with the resistor.

If you wanted to impose some specific point where the LED goes out you can
change the zener voltage.    Keep in mind the LED drop adds to the zener voltage.

[Atodovax]

Just copy of the Boss or Ibanez circuits.   Very basic circuit,  no need for a transistor.

+9V --- 3k9 resistor --- K [5.1V zener] A --- A [LED] K--- GND

You can tweak the brightness with the resistor.

If you wanted to impose some specific point where the LED goes out you can
change the zener voltage.    Keep in mind the LED drop adds to the zener voltage.

Thanks Rob! That one will do it . Have a nice day!

[PRR]

> how the LED Battery indicator of this schematic works? Somehow its not working on my build...

I think it is supposed to "blip" at turn-on if the battery is over 7.5V, then stay out to save juice.

[antonis]

(off-topic, but..)
What's the value of +Vs..??

[Atodovax]

(off-topic, but..)
What's the value of +Vs..??

"9volts - the diode reverse polarity diode drop" . Its intended to be used with a 9v battery.

[Atodovax]

> how the LED Battery indicator of this schematic works? Somehow its not working on my build...

I think it is supposed to "blip" at turn-on if the battery is over 7.5V, then stay out to save juice.

Well it actually does that everytime you plug in the Battery but i guess that is not how it works on the original pedal since its kinda pointless to unscrew the pedal just to disconect And reconnect the leads of the battery to see if its still ok or not. I read somewhere that the pedal should blink until the battery goes below a threshold (7 volts + or -) but never seen an original unit working. The schematic must be wrong, right?

[antonis]

(off-topic, but..)
What's the value of +Vs..??

"9volts - the diode reverse polarity diode drop" . Its intended to be used with a 9v battery.

My bad..
(didn't notice Schottky series diode..)

[anotherjim]

The battery negative is meant to connect to the circuit 0v via the ring contact of a TRS input jack, so the LED will blip "OK" when a plug is inserted when setting up, so no need to open up the enclosure at all.

[PRR]

> pointless to unscrew the pedal just to disconect And reconnect the leads of the battery to see if its still ok  ..... The schematic must be wrong, right?

Two rights don't make a wrong.

Do what Jim says. A lot of wireless microphones do it that way. If it blips at set-up plug-in, it will probably last the whole gig.

[Atodovax]

The battery negative is meant to connect to the circuit 0v via the ring contact of a TRS input jack, so the LED will blip "OK" when a plug is inserted when setting up, so no need to open up the enclosure at all.

Thanks so much! I completely misunderstood the term "Briefly blinks when the battery is ok" from the website hehe... I though it had to oscilate

[Atodovax]

> pointless to unscrew the pedal just to disconect And reconnect the leads of the battery to see if its still ok  ..... The schematic must be wrong, right?

Two rights don't make a wrong.

Do what Jim says. A lot of wireless microphones do it that way. If it blips at set-up plug-in, it will probably last the whole gig.

You are right PPR, my bad to asume that the scheme was wrong.. Wish i had studied hehe.. Thanks for all the help always

[Rob Strand]

You are right PPR, my bad to asume that the scheme was wrong.. Wish i had studied hehe.. Thanks for all the help always

After reading the way the circuit is intended to work it's possible to build something like that.   My biggest beef with the circuit is no current limit on the LED.

This one pulses for about 0.7 seconds.   Diode D3 makes the circuit reset/arm quickly between power ups and protects the transistor from long term damage.



It's possible to do a PNP version.

[PRR]

> no current limit on the LED.

Yeah but. As you say, the pulse is short. Empirically too short to melt the LED or majorly discharge the battery.

Some bad design just works. (And maybe not as parts improve and LEDs lose internal resistance.)

[Rob Strand]

Yeah but. As you say, the pulse is short. Empirically too short to melt the LED or majorly discharge the battery.

Some bad design just works. (And maybe not as parts improve and LEDs lose internal resistance.)

I have a feeling one day it will blow up the transistor and/or the LED.   Virtually unlimited base current (only internal rbb') from cap slamming current into the base,  and if that doesn't get you virtually unlimited LED current.

Makes me cringe like someone over-tightening a wind-up toy  .

[Rob Strand]

Here's a skimped resistor version which can still be submitted for be kind to semiconductors week.



If D3 was removed then R3 would need to be decreased but the side effect of that is the pulse gets shorter as the battery dies.