The Tech Blog

Teardown of Akash Tablet

Posted under DIY, Hacks, Repair, Teardown on December 18th, 2022 by Amaldev

Found this old tablet lying around in our labs. It’s an old Akash tablet (2013 Model). It was designed and manufactured by the Indian company DataWind. It was a $50 tablet launched by the Indian Govt to provide low-cost tablets to students in order to increase access to educational resources and improve learning outcomes. IIT Bombay procured around 100k tablets for distribution across the country.

Coming to the internals and specs. It’s a capacitive 7-inch screen tablet with a front-facing VGA camera. The main processor is an Allwinner A13 SoC (ARM Cortex-A8 1GHz) which runs Android 4. It has a nifty Power Management IC in AXP209, which has 2 DC-DC converters and 5 adjustable LDOs and can support Lithium battery charging upto 1.8A. The I2C interface connects it to the main processor. The device supports WiFi connectivity with a prebuilt Realtek module, RTL8188CTV. It has a pair of 256MB RAM modules(256X8DDR3-WT, I think from HMD). This model seems to have a NAND Flash memory(MT29F32G08CBACA) of 32GB from Micron with a possibility of extending it to 64GB which remains unsoldered on PCB. SSD2532QN6 is the capacitive touch panel controller.

Well, the device is almost 10yrs old, I tried to turn it ON and it doesn’t turn ON without external power plugged in. Seems the battery is in deep discharge(2500mAh capacity) and the protection circuit is preventing charging it up even when I desoldered and tried to charge it separately. I have to remove the protection and bring it to a level then do the normal charge. There is no bulging or anything so I think the battery is fine but as always there is a risk with deeply discharged cells.

Overall the Akash project was an ambitious exercise but the hardware wasn’t upto the mark with a lot of complaints of overheating, boot crashes, software glitches, older specs etc. It never truly reached its potential of being a game-changer for students before the smartphone wave hit the country.

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Back to Basics(With a Twist): SIDAC

Posted under Back to Basics, Educational, Technology on December 11th, 2022 by Amaldev

SIDAC is a specific type of thyristor that is designed to switch on when the voltage applied to it reaches a certain threshold. It is often used in high-voltage applications, such as in power distribution systems. To understand how a SIDAC works, it’s helpful to think of it as a switch that has three states: off, on, and holding. When the voltage applied to the SIDAC’s gate terminal is below its threshold, the SIDAC is in the off state and does not allow current to flow through it. When the voltage applied to the gate reaches the threshold, the SIDAC switches on and allows current to flow through it. Finally, once the SIDAC is on, it remains in the holding state until the current flowing through it drops below a certain level, at which point it switches off again.

It is similar to a DIAC but with higher voltage breakdown regions and current-carrying capabilities(SIDAC = Silicon Diode for Alternating Current). Its a 5-layer PN junction device as shown in pics. Once breakdown voltage(VBO) is reached, it goes to a negative resistance region when current conduction happens. SIDACs are used in relaxation oscillators which are used to create non-sinusoidal waveforms like triangular waveforms. Here a SIDAC is connected in parallel to a capacitor. Initially, the capacitor charges up and when the voltage reaches the threshold of the SIDAC, it makes the SIDAC discharge to obtain your sawtooth waveform whose timing can be adjusted via RC time constants.

Now for the twist, the first paragraph wasn’t written by me. It was generated automatically by the Chat-GPT3 AI service(built on 175 billion parameters). I just gave it an input to explain what a SIDAC is and it gave me the first paragraph as is. An AI model gave me an answer instantly which would have taken me a couple of hours to read up from different papers and books. I am totally mind-blown by what can be done with the tool. It’s going to be used as a companion tool to improve your efficiency drastically(Think GitHub CoPilot). It’s not correct always, it usually gives plausible-sounding but sometimes incorrect answers. If I ran it a few times, I can clearly see it getting some stuff wrong. But possibilities are endless with this tool and I can’t even imagine what it will become 3-4 generations down the lane. All the low-hanging jobs in future will be taken over by AI, in a similar way to how automation killed a large part of manual labour. Start upskilling yourselves in whatever field you are in or you will struggle in a decade or so.

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