Category: History

My 5-volt, tablet-battery-powered, dual-LM386 boombox stereo FM/MP3 music system


LM386 is a mono amplifier IC. I couldn’t find a stereo version of it that was just as robust and simple. So, I designed a circuit with two LM386 chips. That was several months ago.


In the meantime, my BlackBerry Playbook refused to charge. Because of disuse, the battery deep-discharged. There are many videos online offering all kinds of solutions but none worked for me. BlackBerry decided, in their infinite wisdom, to control the charging process using a novel logic, which absolutely refused to charge the battery if the voltage went below some limit. After dismantling the tablet beyond repair, I realized that I could have saved the tablet by opening the plastic cover & directly charge the terminals.

Well… I then had two good tablet batteries and a broken tablet. I decided use it for something. These were high-capacity batteries but like phone batteries output only 3.7 volts.

I got a phone battery charging circuit board that took 5 volts in. It has two LEDs – charging & fully charged. The board also has two load terminals from which you could draw 3.7 volts just like a phone would.

My MP3/FM module requires 5 volts so I added a voltage boost (step up) circuit board.

My attempts to repurpose USB cables from discarded devices failed because they burned off internally during soldering. Hence, I fashioned my own USB cable.

I made a wooden housing for the player. The speakers have neodymium magnets and sound super loud. This is interesting because the stereo LM386 amplifier circuit runs off the same 5 volts. The MP3 module has FM, SD card, line in & USB. It is the same kind as those cheap Chinese FM/MP3 amplifier sets found in autorickshaws.

Use environment-friendly soaps, not detergents

In a previous blog post titled How to make lye soap, I had mentioned that bathing soaps can be made at home. Recently, while shopping in a moffusil area in Kerala, I stumbled upon laundry soap brands.

When I was very young, most households used laundry soaps. Detergent cakes and powders were just growing in popularity. Karsanbhai’s Nirma revolution (inexpensive detergents made out of by-products of IPCL) was yet to take off. Soaps such as the famous 555 came in one long bar, which could be broken off into handy smaller pieces.

What’s the difference? Aren’t detergents and soaps the same? No. Soap is made out of natural oils while detergents are made from petrochemicals.

Washing with soaps involved considerable physical effort – heavy rinsing and beating the clothes over a flat stone surface. Unlike soaps, detergents came with huge mixture of additives that eliminated all that. You just soak the clothes for 15 minutes and with some light rinsing everything became clean. It did not form scum like soap and worked well with hard water. Vegetable oils are anyway expensive while petroleum byproducts was dirt-cheap. Over time, detergents replaced soaps in popular use. However, detergents are not environmental friendly. The by-products of detergents washing cannot be broken down. It pollutes the groundwater. Many detergents come with protein-dissolving enzymes which will destroy skin & tissues if used for manual washing that is not in a washing machine. Perfumes used in detergents are also harmful.

Laundry soaps are still being manufactured as a cottage industry by Khadi and rural self-help groups. They are not expensive either. Don’t be a baby if you don’t see bubbles. These soaps can clean clothes all right.

Two washing "soap" brands available in mofussil areas of Kerala.

Two washing “soap” brands available in mofussil areas of Kerala.