The 555 timer – part 2

Today we’ll look at a couple more versions of the 555 timer. Like the 741, this chip has been produced by many different manufacturers in the nearly five decades since its introduction by Signetics in 1972.

First up is RCA’s CA555. Packaged in an 8-pin DIP (which is what the “E” in “CA555CE” stands for), this is a “C” spec which can work at up to 16 V, unlike the CA555E that is spec’ed up to 18 V. I’m not sure what the actual difference between these two would be; I guess the chips were sorted after production, with parts that marginally failed some spec at 18 V being demoted to “C” versions.

Continue reading

ST LIS3DH Accelerometer

The LIS3DH is an accelerometer, designed and manufactured by STMicroelectronics. Like most accelerometers today it is a MEMS device (Micro-Electro-Mechanical Systems), which means the sensing function is made from silicon and integrated into an IC process. Special etching techniques are used to create tiny moving parts that can bend in certain directions, along with sensors that can detect that movement.

MEMS accelerometers are used in many electronic devices: your phone that detects whether you’re holding it horizontally or vertically, your games console that can sense which way you’re moving the controller, or your car that can detect the speed and direction in which you’ve just crashed so it can properly deploy the airbag.

The LIS3DH is housed in a little LGA package that measures just 3 x 3 mm2. Oddly there’s no ST logo or marking on the package. The “ON5nn” production code could actually trick you into thinking this is an ONSemi part.

Continue reading

The 741 op amp – part 4

After a bit of browsing on eBay I found several “new” versions of my favourite classic op amp, the 741. We’ve already seen about twelve different layouts so far, but today we’ll see that there are still more out there.

Starting with the oldest, we go back more than four decades to 1974. Texas Instruments at that point sold the SN72741, adapting the original Fairchild part number to their own nomenclature: SN stands for “Semiconductor Network”, meaning “integrated circuit”, while the numbers indicate the product series and temperature range (0 to 70 °C in this case; there was also an SN52741 with a wider temperature range).

Continue reading

The TT555: a discrete 555 timer plug-in replacement

After dissecting a whole batch of 555 timer ICs I thought it would be an interesting project to make a working copy of the 555’s internal circuit out of discrete components, in the same physical space as the original IC. I’ve done this before with the 741 opamp, and the steps are similar. First, I drew the schematic in KiCAD:

I used the original circuit as designed by Hans Camenzind, as a tribute to his design but also because it uses the smallest number of transistors among all different designs I found while dissecting the various 555 ICs. Discrete transistors are larger than discrete resistors, so the original design saves space compared to newer versions that include several more transistors. Note that it’s the opposite situation when you’re designing an actual IC: integrated resistors are usually the largest parts in your layout.

Continue reading

The 555 timer

If there’s a classic analog chip even more iconic than the 741 op amp, it has to be the 555 timer. Released just three years after the 741, it similarly took the world by storm, selling billions of units over five decades. Quite unlike the 741, which established op amps as a common IC type, the 555 has remained largely in a class of its own. There are many ICs that can generate square or triangle waves, but I can’t think of any chip that can function as a one-shot, a flip-flop, Schmitt trigger, or one of a million different oscillator types like the 555 can.

Designed by Hans Camenzind in 1972, its story is described in detail in Camenzind’s own book Designing Analog Chips. I highly recommend reading it (available on paper or as a free download) if you’re interested in analog IC design. In Chapter 11, Camenzind shows the schematic of the original 555 timer:

Continue reading

The TT741: a discrete plug-in 741 replacement

Regular readers of this blog will have noticed that the 741 op amp features quite often. Apparently I’m not the only one with an interest in this venerable amplifier; the Wikipedia page on op amps contains a detailed description of the 741, several books and web sites describe and even celebrate the chip’s history, and you can buy a kit to make a large-size discrete replica from a company called Evil Mad Science Labs. I bought one of these because I thought it looked rather cool.

On the picture above you can see the 741SE compared to an original LM741. I got the SMD version of the kit, although you can also buy one that uses through-hole components and is shaped like a giant DIP package. Still, even the SMD version is enormous compared to the real chip, which got me thinking: would it be possible to make a discrete equivalent of the 741 in a space equivalent to an actual DIP chip?

Continue reading

Fake (?) IR2104

I recently read a discussion on an electronics forum where someone had trouble getting an IR2104 to work correctly. He had bought these from a shady online store and could not get the correct signals to come out. I offered to analyze the chips, and one of the contributors to that discussion very kindly sent me a couple of them.

The IR2104 is a half-bridge MOSFET driver, which is used to drive the FETs in circuits like DC-DC converters and class-D power amplifiers. It’s made in a high-voltage CMOS process and is capable of driving the high-side FET at voltages up to 600V. The original designer and manufacturer is International Rectifier (IR), one of the first manufacturers of diodes, transistors and power management ICs. Currently the IR2104 is manufactured by Infineon, after it acquired IR in 2015.

Continue reading

Second-source 18B20s

A while back I dissected the Maxim DS18B20 temperature sensor, along with a counterfeit one. Today we’ll have a look at a couple more 18B20s from different manufacturers, all of them Chinese. I found a web store in China that sold me the XSEC SE18B20, the Novosense NS18B20, the 7Q-Tek QT18B20, the GXCAS GX18B20W and the UMW (Youtai) DS18B20. Prices varied from 65 cents to about two Euros apiece.

To get an idea of their performance, I put one of each on my Arduino board and placed it outside, where it was quite cold:

Continue reading

Raspberry Pi Pico

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.

Continue reading