LCD drawing too much current?

Today I finished my third Shruthi. With this unit I tryied to do something more complicated (for a noob like me) than simple kit assembling adding the two pots (gain and volume) and a on-off-on switch to let the unit be run by either wallwart or battery (we talked about it here)

The problem is that when I feed the Shruthi with a 9V battery it starts in the right way with everything that lights properly, but after 30 seconds the LCD starts fading out just like I’m turning the contrast trimpot to the zero; when the text on the screen is non more readable the backlight is still lit.

Any idea of what happens?

That’s what happens when my batteries start to die.

Do you have a way of tracking the voltage of the battery?

It was my first suspect, but after some tests with some spare batteries I had around I used a brand new one which was still sealed in its package. The result was exactly the same: 30 seconds and than fading of the text on the screen.

I have a voltmeter. I suppose I have to track the battery detached from Shruthi… I’ll let you know.

I would do both, battery disconnected, and connected… And also connected after 30+ seconds…

If you have a meter, there should be a function to measure current draw.

Here is what I read:

a) detached battery - 9.34V
b) connected battery with Shruthi off - still 9.34V
c) turning Shruthi on - immediatly falls to 7.30V and then starts a constant falling at a rate of 0.01V per second.

Another strange thing I realise only now. The right pin of the on-off-on switch is connected to the higher SW pad (near dc jack), the center pin is connected to the lower SW pad (near 1N4004), the left pin is connected to the battery (+), while the battery (-) leads to the ground pad near the Lowww trimpot.
Well, what I expect is that if I pull the switch to the right it feeds current from the dc jack, while if I pull it left it ler the battery to feed the unit (obviously center is the “off” position).
What is strange? That, in reality, if i pull right Shruthi is battery powered and, on the contrary, left let the wallwart current flow.

I have to admit I’m a bit confused right now… I missed somenting but I don’t know what.

Post of pic of how it is connected, it sounds like you are shorting out the battery. Switches are supposed to be that way, the “on” position wiring is opposite to the switch position (i.e. if you want -o to be on you wire X#-# those two terminals)

Here is the pic of the connections I did.

Shruthi connections

The strange thing I realized is when I toggle the switch to the right (looking the picture) it should let the current from the dc jack feed the Shruthi; what happens instead is that Shruthi is fed by the battery. Of course if I toggle the switch to the left the opposite happens.

no that’s correct. the switch always switches on the lug opposite to the lever’s direction.

I didn’t know it. Thanx for the hint Rosch. What about the other connections? Are they right or I screwed up something?

i’m not sure, on the pic it looks like you’re switching the DC power in either to the battery + or the PSU negative in, but i probably get it wrong.

usually you put the battery+ on one side and the psu+ on the other. then wire the middle lug to the following circuitry. i don’t know for sure if it would be better to do the same with the negative inputs, so that one power source is always entirely disconnected when using the other.
(a DPDT on-off-on switch would probably be the best choice then, middle position disconnects both)

edit edit:

the DPDT wiring would then be like this: