technology – Tim's Blog

A surprising IC in a LED light chain.

LED-based festive decorations are a fascinating subject for exploration of ingenuity in low-cost electronics. New products appear every year and often very surprising technology approaches are used to achieve some differentiation while adding minimal cost.

This year, there wasn’t any fancy new controller, but I was surprised how much the cost of simple light strings was reduced. The LED string above includes a small box with batteries and came in a set of ten for less than $2 shipped, so <$0.20 each. While I may have benefitted from promotional pricing, it is also clear that quite some work went into making the product cheap.

Neural Networks (MNIST inference) on the “3-cent” Microcontroller

Bouyed by the surprisingly good performance of neural networks with quantization aware training on the CH32V003, I wondered how far this can be pushed. How much can we compress a neural network while still achieving good test accuracy on the MNIST dataset? When it comes to absolutely low-end microcontrollers, there is hardly a more compelling target than the Padauk 8-bit microcontrollers. These are microcontrollers optimized for the simplest and lowest cost applications there are. The smallest device of the portfolio, the PMS150C, sports 1024 13-bit word one-time-programmable memory and 64 bytes of ram, more than an order of magnitude smaller than the CH32V003. In addition, it has a proprieteray accumulator based 8-bit architecture, as opposed to a much more powerful RISC-V instruction set.

Is it possible to implement an MNIST inference engine, which can classify handwritten numbers, also on a PMS150C?

Decapsulating the CH32V203 Reveals a Separate Flash Die

The CH32V203 is a 32bit RISC-V microcontroller. In the produt portfolio of WCH it is the next step up from the CH32V003, sporting a much higher clock rate of 144 MHz and a more powerful RISC-V core with RV32IMAC instruction set architecture. The CH32V203 is also extremely affordable, starting at around 0.40 USD (>100 bracket), depending on configuration.

An interesting remark on twitter piqued my interest: Supposedly the listed flash memory size only refers to a fraction that can be accessed with zero waitstate, while the total flash size is even 224kb. The datasheet indeed has a footnote claiming the same. In addition, the RB variant offers the option to reconfigure between RAM and flash, which is rather odd, considering that writing to flash is usually much slower than to RAM.