9V Low Battery Indicator (Layout)

Crodor · Post by **Crodor** » 24 Oct 2023, 13:35

Simple low battery indicator for usage in a bass guitar with active pickups. LED lights up when battery voltage is below 7V, indicating that it's time to change the battery,

bmxguitarsbmx · Post by **bmxguitarsbmx** » 24 Oct 2023, 15:38

Please post the schematic so we can encourage learning electronics, not just mindlessly "painting by numbers".

Crodor · Post by **Crodor** » 24 Oct 2023, 19:08

Of course - here we go

Intripped · Post by **Intripped** » 24 Oct 2023, 20:29

Layout and schematic are not coherent with eachother.
According to schematic, R5 should be connected to R1-R4 junction

Crodor · Post by **Crodor** » 24 Oct 2023, 20:53

Uups, you are right. I know that the vero works, so I replaced the schematic with an updated one, now it should be ok. Thanks!

Lani · Post by **Lani** » 25 Oct 2023, 10:30

You also might consider switching the two series resistors R1 & R4 (73k) to something more commonly available like 30k and 43k.... Not sure I've seen a 40k resistor before. I suppose you could use (x2) 20k + 33k.... Really just thinking out loud now....
Either way, Welcome!! (Where are my manners

) Thanks for the layout & schematic

twotees · Post by **twotees** » 25 Oct 2023, 13:53

How much power does it draw while monitoring the 9V Battery? Last thing you need is a battery monitor that flattens your battery!

ppluis0 · Post by **ppluis0** » 25 Oct 2023, 14:43

twotees wrote: ↑25 Oct 2023, 13:53 How much power does it draw while monitoring the 9V Battery? Last thing you need is a battery monitor that flattens your battery!

If my math is correct, this circuit draws 0.386mA with a fresh battery (led off) and increase to 0.828mA when the led lights on at 7 volts of battery.

Perhaps with high resistor values the same job can be done with a couple of 2N7000 mosfets ?

Cheers,
Jose

Lukasen · Post by **Lukasen** » 25 Oct 2023, 20:45

I would not like to take away the enthusiasm of all those who are enthusiastic about DIY, but it seems the easiest to use a so-called supervisory circuit, for example from here: https://cz.mouser.com/c/semiconductors/ ... ock=y&sort =threshold%20voltage .

Another option I can think of is a comparator circuit (either from a comparator or a very low draw opamp).
I found something here for inspiration: https://www.eleccircuit.com/simple-led- ... ttery-low/.

mozz · Post by **mozz** » 25 Oct 2023, 21:42

: 105-0252-001.jpg (6.98 KiB) Viewed 5907 times

Lukasen · Post by **Lukasen** » 27 Oct 2023, 19:47

There are more ways how to do.
So there is first simplest: TC54VC4302ECB713 (SOT-23) https://www.mouser.com/ProductDetail/Mi ... dWJA%3D%3D
Supply current is 1.1uA, cool.

There is some info about the using: https://stompville.co.uk/?p=200.

And there is second option, which I found it.
So just a basic simulation and a list of low power opamps and comparators. This scheme was also in the datasheet of one of them about the application. The threshold from simulation was set to 7.4V (the preferred value will depend on when the sound from the active electronics starts to distort).

george giblet · Post by **george giblet** » 08 Nov 2023, 02:06

Lukasen wrote: ↑27 Oct 2023, 19:47 And there is second option, which I found it.
So just a basic simulation and a list of low power opamps and comparators. This scheme was also in the datasheet of one of them about the application. The threshold from simulation was set to 7.4V (the preferred value will depend on when the sound from the active electronics starts to distort).

Not enough current through the zener to make it reliable or predictable. (Simulators do not model zeners at low currents well)
More current through the zener means the indicators circuit will then start to drain the battery!

It's possible to use a MOSFET as a poor mans reference which would run on low current. LEDs might work as will but they will need a minimum current.

Lukasen · Post by **Lukasen** » 08 Nov 2023, 19:47

george giblet wrote: ↑08 Nov 2023, 02:06
Lukasen wrote: ↑27 Oct 2023, 19:47 And there is second option, which I found it.
So just a basic simulation and a list of low power opamps and comparators. This scheme was also in the datasheet of one of them about the application. The threshold from simulation was set to 7.4V (the preferred value will depend on when the sound from the active electronics starts to distort).
Not enough current through the zener to make it reliable or predictable. (Simulators do not model zeners at low currents well)
More current through the zener means the indicators circuit will then start to drain the battery!

It's possible to use a MOSFET as a poor mans reference which would run on low current. LEDs might work as will but they will need a minimum current.

Thanks for the info and sorry for the wrong schematics. I did not fully realize the characteristics of the Zener diode.

And I found this topic addressed with a schematic here: viewtopic.php?t=31502.

george giblet · Post by **george giblet** » 09 Nov 2023, 06:45

Lukasen wrote: ↑08 Nov 2023, 19:47 Thanks for the info and sorry for the wrong schematics. I did not fully realize the characteristics of the Zener diode.

And I found this topic addressed with a schematic here: viewtopic.php?t=31502.

The voltage reference on that circuit (ZXRE330), is designed to work at very low currents, > 1uA,
https://www.diodes.com/assets/Datasheets/ZXRE330.pdf

mozz · Post by **mozz** » 12 Nov 2023, 15:42

Just found this out in the garage, don't know what volts it is set for. 2n2222 transistors, so mostly the same as the original post?

george giblet · Post by **george giblet** » 12 Nov 2023, 21:20

Just found this out in the garage, don't know what volts it is set for. 2n2222 transistors, so mostly the same as the original post?

The original uses the transistor VBE voltage as the reference voltage and tries to keep the currents low.

Your circuit is something like this one:

: LED Voltmeter - sch.png (6.82 KiB) Viewed 5134 times

There's a few circuits like this around, for example this one for monitoring a car battery (note different use of LED colors),