7th
AUG

Make a Bluetooth speaker

Posted by Mohammad Forgani under Electronici:

I’m using BK8000L Bluetooth module (SBC audio decoding performance) and as amplifier the PAM8403  board. (but you can use any other amplifier for example from you old PC speaker)

Problem with feedback and noise

If  we want to power the both devices from the same power supply, It will get a lot of noise. (ground loop noise)
To eliminate sound noise we should using separate power supply to drive the Bluetooth and amplifier.

Main component are:
– Bluetooth Stereo Audio Module Transmission BK8000L
PAM8610 2x15W Amplifier Board Digital
– Power supply ca 7 to 9V for PAM8610 and 3.3v for Bluetooth
– Two speakers

For 3.3V power for BK8000L I used a simple USB/AC Adapter charger and with a AMS1117 Voltage regulator convert the 5 volt output to 3.3 volt.
Keep in mind to added 100 uF and .1 uF capacitor between VCC and GND.

Recommend is to use a 100uF/25V electrolytic capacitors between VCC and GND.

22nd
JUL

Notebook power supply modification

Posted by Mohammad Forgani under Electronici:

 

Modification of IBM notebook power supply

How can I modify  the output of power supply from 16.8 to 12 volt?

Most of the switched mode supplies are normally provide with a reference voltage to regulate the output, which is the heart of the device.

Identify the voltage divider:

First I opened the case and looked for the feedback circuit and voltage divider.

Then, I tried to locate the two resistors that are responsible for setting  the output voltage.

The stabilization of the output voltage can be archived in the same way as TL431 (TL431  will be used in chip switching mode supplies and you can find many documents about its functionality in internet).

Vo=Vref*(1+R1/R2)

I already knew, that the location these two resistors can be found near the opt-coupler.

Only R1 is interesting for me. I can simply add an additional resistor in parallel to it and reduce the total value.

The resistor Rx51 on board as you see in the picture can be a good candidate. I measure the value and it was 976 ohm .
Measure the voltage at the opt-coupler was about 1.9V

 

On the left side of the board I found a tiny circuit board, which is shown in the picture. I assume its functionality is the same as TL431.

Additionally, on the tiny broad I found the resistor R62 with 1.9 K in series to RX51.

I soldered parallel to R62 (1.9K) a new 6.8K resistor.
The result was 1.4K and gave me an output of 11.8 Volt and max 3.4 Amper

 

 

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