Although the 555 timer is one of the most iconic chips ever made, and the original version is still sold in huge numbers, it actually makes little sense nowadays to use the original version anymore. That’s because an improved version has been around for a long time: the CMOS 55 timer. Most manufacturers that produced the original bipolar 555 timer also make a CMOS version, with typically the letter “C” somewhere in the full product name. Today we’ll have a look at a couple of these CMOS timers and see how they differ from the classic model.Continue reading
Most electronic systems that need an accurate clock, which is to say most microprocessor-based systems, use a quartz oscillator. You’ll typically see a metal package somewhere near your chip that contains a slice of quartz which resonates at a certain frequency thanks to the piezoelectric effect.
Quartz crystals are cheap and provide a very accurate clock frequency, but they take up quite a bit of space and are sensitive to shocks. To deal with those two problems, fully on-chip oscillator systems have been available since about 2010. These use micro-electro-mechanical systems (MEMS) technology, which involves the manufacture of tiny moving structures on a chip. Their price is typically higher than that of a quartz crystal however, and their frequency stability and phase noise performance are often a bit worse. Today we’ll have a look at a few different MEMS oscillator chips and see what they look like inside.
First up is the Si501 by Silicon Labs. It’s an 8 MHz oscillator built using what Silicon Labs call CMEMS technology, which means that they integrate the MEMS bit on the same chip as the rest of their circuits. The package looks rather anonymous, with just a cryptic part number and no manufacturer’s logo. Silicon Labs have since sold their MEMS oscillator business to Skyworks, so future versions of this chip might have a different marking.Continue reading
I recently read a forum thread where someone showed how a set of LME49710s that he bought online didn’t function the way they should. Although the chips apparently contained an op amp, they were unable to amplify a 60 kHz square wave and output a triangle wave instead. This means that the op amps’ slew rate is too low: the LME49710 is specified to reach 20 V/us, but these chips only managed 0.5 V/us or so.
The thread’s author asked if anyone could help identify his chips, and I offered to examine them for him. A few days later I received the op amps in the post. They were clearly marked with the National Semiconductor logo and “49710” as a model number:Continue reading
TT555 Soldering Kit now available on Tindie!
Probably the most-viewed post on this blog so far has been my project to construct a discrete-transistor replica of the 555 timer IC. I’m pleased to report that, due to popular demand, the TT555 is now available in kit form!
This is your chance to prove that you’re a real SMD soldering expert: to assemble it, you need to place 43 components onto a 10×10 mm2 PCB, pick and place 01005 size resistors (0.4×0.2 mm2), and solder DFN-1006-3 packages (1.0×0.6 mm2). A microscope, sharp tweezers and a fine-tipped soldering iron are essential tools to complete this project.
Please click here to find the TT555 on Tindie!Continue reading
First Alert Smoke and CO Detector
I bought this smoke and carbon monoxide detector several years ago, and it’s been doing its job just fine ever since: mostly being silent, screaming when I burn my toast, and beeping every two years or so when its batteries run out. Recently however it began beeping for no reason, and I couldn’t get it to stop other than by removing the batteries. So I bought a new one and decided to tear down the old one.Continue reading
TI LPV801 and LPV821
Back in 2016, TI introduced a line of what they called “nanopower op amps”. Where older op amps like the 741 use around 2 mA, and more modern ones might reduce that to perhaps 100 uA or so, TI’s ultra-low power devices consume just a few hundred nA. This enables the design of things like smoke alarms and temperature monitors that can work for a decade on a single battery charge.
This is the LPV801, a single channel op amp that uses just 450 nA. It’s not very fast: with just 8 kHz of unity-gain bandwidth it’s useless for audio, but ideal for slow-moving things like temperature sensors. A dual version (LPV802) is also available, as are single and dual versions with reduced offset voltage (the ‘811 and ‘812 respectively).
Inside we find this neat little design. Five bond pads are bonded to the five pins on the package; two additional ones on the top row are used for testing. In the top-right corner is an L-shaped alignment marker, which is used during laser trimming.Continue reading
Philips LED Bulb
LED light bulbs are the most commonly sold type nowadays, especially since incandescent bulbs have been gradually banned from sale starting around 2009. Other low-power types like halogen and compact fluorescent bulbs were also commonly sold until a few years ago, but advances in LED technology, along with a precipitous drop in price, have made LED bulbs the most common type by far.
This 5.5 W, 470 lumen bulb had been lighting my home for a couple of years until it burned out a month ago. It was one of the cheapest types sold under the Philips brand; I don’t recall exactly how much I paid for it, but it must have been around eight euros or so. Philips, founded in 1891, is one of the oldest manufacturers of light bulbs, although all lighting products were spun off into a separate company called Signify in 2016.
If we cut off the translucent plastic dome, we find a small PCB carrying the LED chips. It’s screwed onto a thick aluminium body that acts as a heat sink. There are five LEDs mounted on the board, but as we can see there’s place for three more. Clearly, the same basic design is also used for a higher wattage version that contains eight LEDs.
All LEDs are connected in series; the three unused ones are bypassed by two zero-ohm resistors (JP1 and JP2). In the middle is a two-pin connector that supplies power from a regulator PCB in the base of the bulb.Continue reading
π120u30 Digital Isolator
Digital isolators are a modern replacement for optocouplers: components that can bring a signal from one place to another without connecting those two places electrically. They’re essential parts in equipment that connects to a dangerous voltage on one end (mains power usually) and comes into close contact with something sensitive on the other (humans, usually). Since they’re safety-critical components, manufacturers show off all kinds of safety certificates and qualifications to convince their customers that their isolators won’t electrocute anyone by mistake.
Today we’ll look at one of the cheapest digital isolators out there: the π120u30, made by 2Pai semiconductor, which costs less than 20 cents in large quantities.Continue reading
Texas Instruments has a nice selection of motor driver ICs. Where in the old days you’d often have to make your own H-bridge out of discrete transistors, figure out how to drive their gates, and then generate the right signals to spin up, reverse, brake or coast your motor, nowadays you can get all these functions integrated into a single chip. Today we’ll look at the DRV8876, which is a rather small chip that can nevertheless dump up to 3.5 A into a motor’s windings.Continue reading
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