The Raspberry Pi Pico is the latest in the Raspberry Pi series of single-board computers. Introduced in January of 2021, the Pico marks a significant change from the earlier series: instead of having a Broadcom system-on-chip, the Pico’s heart is a custom IC with a dual-core ARM Cortex-M0 processor at 133 MHz. Combined with its tiny form factor and lack of interfaces like HDMI, it feels more like a supercharged Arduino than a small PC.
This is the Pico. It contains the main CPU in the centre, 16 Mbits of flash memory next to it, a DC/DC converter on the right, and a USB connector to program the whole thing. I/O pins are scattered around the edge to enable easy interfacing to its environment.
The 486DX series were the complete, full-performance versions of the 486 processor line. Unlike the low-cost 486SX, the DX versions contain an FPU, which significantly speeds up floating-point calculations compared to the earlier 386. In 1992 Intel delivered another huge leap in performance by simply doubling the clock frequency of the 486 core from 33 to 66 MHz. Motherboards at the time could not cope with such high speeds, so the bus clock remained at 33 MHz. Although 40 and 50 MHz speeds were also available, the 66 Mhz version was by far the most common and remained the processor of choice for most high-performance 486 computers until Pentium systems became mainstream around 1995.
The DS18B20 is a digital temperature sensor that communicates through the One-Wire protocol. Like the DS2401 that we looked at earlier, it is housed in a three-pin TO92 package and can be read out using just one pin (plus ground). It’s made and sold by Maxim Integrated, although still labelled “DALLAS” on the package. Introduced in 1999, the DS18B20 was the successor to the DS1820 and provided a higher resolution (up to twelve bits, instead of the DS1820’s nine).
This part has become wildly popular over the past few years, because it is reasonably cheap, quite accurate, and very easy to use with microcontrollers. It is widely available online, but its popularity has, unfortunately, also given rise to an industry of fake DS18B20s. Although they usually work, there is no guarantee that they meet the specs listed in Maxim’s datasheet.
These fake chips are made by small semiconductor companies that have designed a drop-in replacement for the Maxim part, copying the exact functionality. There’s nothing wrong with second-sourcing a part like that (it’s how many semiconductor companies started in the first place), but marking them with the Dallas brand and selling them as if they’re genuine Maxim parts is of course illegal. Most likely it’s not the manufacturers that apply the fake label, but shady companies that buy large stacks of second-source chips, re-label them and sell them as if they’re the real thing.
Since writing the first post on this blog about the 741 op amp I’ve managed to get my hands on a few more 741s to dissect. Three of these I bought new, and two more I found back in some forgotten corner of my lab.
First up, a brand new National/TI LM741. Although National Semiconductor was acquired by TI in 2011 and they stopped using the National brand soon after, the LM741 that you can buy in 2020 still has the National logo on it. I can’t figure out why though, because changing the logo on the package is as simple as reprogramming a printer (which happens anyway because it needs to print a new date code every week or month).
