Amplified Mini Speaker Modifications

[mikkut]

Hi All,

I have an analog amplified mini speaker that I would like to make some modifications to:

The amplified mini speaker as is out of the box:
-There is an internal battery that is charged when connected via micro USB . The speaker cannot operate when the battery is charging
-There is a push button on/off switch
-analog audio in is through a 3.5mm male jack (not through USB port)

What I would like to end up with:
-eliminate the battery and have it powered via hard wire to a DC power source (can be a separate wire, does not need to utilize existing micro USB port)
-eliminate the power switch so that is simply on when power is supplied and off when power is disconnected. I tried disconnecting the existing battery and connecting to a DC power supply and the speaker worked fine BUT it still requires turning on the power switch. And when the power is disconnected it appears the power switch re-sets so turning on the power switch is required every time power is connected.

No changes needed on the audio in and audio out.

Thanks!!

 

[gophert]

First step,
Check if you press the power button and hold it in while you plug in the speaker - does it power up or do you need to press the button after the power is applied?

 

[mikkut]

need to press button after power is applied...

 

[Nigel Goodwin]

need to press button after power is applied...

Going back decades, I've used 555 timers to 'press the button' after power is applied.

 

[gophert]

need to press button after power is applied...

Second Step:
I assume you have a volt meter.
a button like this triggers a a logic device. The important part of your switch will bring the voltage level from 0V to battery+ when pressed or battery+ to 0V. (I am assuming battery+ is the operating voltage and no additional voltage regulation but let's find out.

use your volt meter (voltage setting) and put the black lead on the "B-" solder pad and red lead on the various switch terminals (in your photo, the top pair and bottom pair should behave the same because they are electrically connected). As follows (keeping black meter wire on B-, report back with
- voltage when red is connected to top button solder pad (with and without button pressed
- voltage when red is connected to bottom button solder pad (with and without button pressed)
I assume battery is charged.

now, set your meter to "ohms" and measure resistance from
- B- to top button solder pads
- B- to bottom solder pads
- B+ to top solder pads
- B+ to bottom solder pads