555 timer teardown (and a Retrovoltage drum trigger project)

Ken Shirriff’s blog has a fantastic and detailed teardown of a 555 timer, the ubiquitous decades-old timer circuit that turns up in so many places:

If you’ve played around with electronic circuits, you probably know the 555 timer integrated circuit, said to be the world’s best-selling integrated circuit with billions sold. Designed by analog IC wizard Hans Camenzind in 1970, the 555 has been called one of the greatest chips of all time with whole books devoted to 555 timer circuits.

Given the popularity of the 555 timer, I thought it would be interesting to find out what’s inside the 555 timer and how it works. While the 555 timer is usually sold as a black plastic IC, it is also available in a metal can, which can be cut open with a hacksaw revealing the tiny die inside.


via 555 timer teardown: inside the world’s most popular IC.

Ken takes us through the history, use, die, and individual transistor circuits implemented on the die on his blog. It’s a fascinating read well worth spending an hour exploring.

I don’t get into 555s that often myself, but last summer Retrovoltage built an LED flasher circuit centered around a 555 for local Seattle band Breakaway Derringer‘s drummer. (They’re a great band that’s worth checking out if you enjoy cowboy punk rock!)




The 555 operates in single-shot mode, driven by a drum trigger sensor to switch on a TIP31C power transistor supplying power to LED strips.

The drum project was based on an Instructable that he found. You can find that Instructable here…but if you do, pay careful attention to the pin numbering on the schematic, which borders on nonsensical and definitely does not match the physical layout of the chip.


He’s only using one, but you can do some pretty neat effects with this idea.

Building the SSTRAN Part 15 Low Power AM Transmitter Kit

Have a bunch of old tube radios, but nothing good on the air in your area? That’s a common problem, and SSTRAN has the solution! I just built one of these to give as a gift, and thought I’d write up the experience. It’s a somewhat complex kit to build with quite a few parts, but if you’re decent at soldering and have some patience, you shouldn’t have any trouble.



Everything came neatly packaged in a box with a detailed set of instructions. Inside, the parts were kitted out based on their type and which step of the build process they’d be useful.



The instructions are very detailed, including which color codes you can expect to find on the coded parts, and the assembly steps follow a logical path building up the bare PCB. There are even tips about how to get the best solder joints and soldering techniques on the plated through-hole board.


One chip, a surface mount IC, came pre-soldered; everything else was for the recipient.


I followed the instructions, documenting each step along the way. Resistors first:




Small chokes next:



Rectifiers and small-signal diodes:



Next up was the resistor network, a set of 9 x 10K resistors in a SIPP arrangement with a common pin.



The board is starting to fill up! Next up were the IC sockets. This is always a nice touch – it’s easy enough to put ICs directly on the board if you’ve perfected your technique but can be tricky, and it’s easy to burn up an IC by accident. Sockets make it easy to fix a mistake.


Jumpers and switches next. Later these are used to set the frequency range according to tables in the back of the manual.


Next up were the small fixed capacitors:



Getting there!


Just a few more parts: jacks, the ceramic trimmer for the output circuit, front panel controls, and some other bits.





Transistors were one of the last items to finish on the board:


Followed by big power supply chokes:


Last was the voltage regulator’s heat sink, and the crystal.


Time to fire it up!



The transmitter accepts L+R audio input, downmixed to mono internally, and a power supply; the antenna and counterpoise are also connected via an RCA jack. There are adjustments for audio gain, audio compression, and modulation. These controls interact somewhat, and vary a bit depending on what you’re using to receive, so tend to need to be tweaked for best sound quality once you’ve got the system on the air.

The next step was to tune the output. The construction manual lists an easy procedure to measure a voltage across a set of points while adjusting the trimmer. Here I did diverge a bit to use my spectrum analyzer with a small antenna and measure the output that way, since I had already been using the analyzer earlier.


Finally, it was time to snap it together into its case:



All done!


This was a very straightforward project to assemble, and I expect it should be able to be completed by anyone. It took me about 4 hours to complete this project (stopping to take photos along the way); if you’re on a mission I think it could be done in as low as 2 hours. If you’re pressed for time or are new to the hobby and want to go slowly, it’s easily divided up into steps which you can work on one at a time, a few minutes a day, until you’re finished.

As far as performance, it sounds great playing through a selection of vintage tube radios – just like it’s supposed to! I’d highly recommend this kit if you need a low powered AM transmitter solution for your own collection.


Building a Better Voltage Regulator

Glancing through my feeds, I stumbled across a note on The Paleotechnologist describing a new replacement for the venerable LM7805 linear regulator IC. It turns up in a ton of devices, pretty much anything with a medium-current 5V rail including some stereos, computers, power supplies…mostly anything you can think of. And the old version isn’t that efficient:

Take the LM7805, for example. It does a good job of regulating voltage — from a minimum of about 7V or so, it will provide a steady 5VDC output. The only real problem is that it does this by basically adding a dynamic resistance to simply burn off the excess voltage at whatever current you’re using. If you were to power a 5V, 1A load through a LM7805 connected to 12V, it would need to dissipate 7W of power, since it would basically be acting as a resistor; that 7V voltage drop, combined with the 1A of current, means it would be putting out 7W of heat. Without a BIG heatsink, it would quickly get too hot to work. Also, you’d be wasting over half of the power for the device, even if the rest of your circuit was 100% efficient.

via A Better Voltage Regulator | The Paleotechnologist.

Looks like CUI came out with a new, drop-in 7805 replacement which implements a DC-DC switching converter for voltage regulation, rather than a linear regulator. Way less heat and lost power with this module! I’ll probably spec it in future projects if I end up needing to replace a 7805 in some old gear, looks very interesting!


The folks over at Hack-a-Day have already found a hobbyist who put this module through it’s paces. Daniel over at Daniel’s Electronics Blog does some bench testing the switching drop-in replacement for the 7805. to test it’s efficiency.


The graph of efficiency versus load is shown below, the peak efficiency is around 92%. Not bad for a 12V input.


Not bad for a 12V input indeed, the linear chip would be wasting a ton of power as scorching heat with the same conditions.

The Paleotechnologist: A Better Voltage Regulator


Daniel’s Electronics Blog: Testing a DC-DC Converter Module

Idea Poll: A tutorial on buying parts online?

Once again, I’ve been asked “Where do you buy your parts?” and that’s a question that comes up very regularly. (My answer? Mouser.com, of course.)

I’ve heard from quite a few people over the years that Mouser.com can be intimidating for new hobbyists to navigate, though, and I can understand it. They sell everything under the sun for electronics and it’s designed primarily for professionals. The ecosystem of smaller vendors selling curated selections of common capacitors, resistors, etc. with simple, friendly websites (and a somewhat higher price) serves as further support for this position.

Really, though, for many if not most types of parts you’ll buy for common radio and stereo repairs there’s not much to it and once you’ve seen it once or twice it’s second nature.

If I went through and wrote a tutorial on how to navigate Mouser.com and find common parts, is that something anyone would find useful? I imagine that of the people reading this blog, there’s a mix of advanced hobbyists and professionals who already know the drill alongside casual hobbyists and beginners who might not have taken the time to explore it just yet.

What do you think?

How to Read Capacitor Codes

I ended up with a massive stash of mil-spec CDE Mica caps recently, and was searching for a refresher on decoding their military part numbers like “CM05FD221GP3”, since the caps came marked for their values but not their voltage ratings.

I stumbled on the Xtronics Wiki page about reading capacitor codes, which has all the info I needed, and more. It has instructions on reading EIA and Miiltary codes, and tables of the tolerance, delectric materials, temperature coefficients and ranges, and working voltage codes.

Turns out, those are 500V CDE Mica caps, 2%, and with a +/- 0.05%+0.1pF capacitance drift over temperature. Not bad!

If you need a quick reference for all these different codes, definitely check out the Xtronics wiki.

It’s good to have adapters!

I’m working on a little amplifier from the late ’60s, maybe very very early ’70s, which uses RCA jacks for the speaker output connections. It was most commonly found on very economical and low-powered systems. (The one in question is 10 W per channel, definitely low power.)

Fortunately, a quick dig into the parts drawer turned up some RCA plug shells and a few minutes later, ready to connect.

Easy enough! I won’t be using this one very often, but it joins my collection of speaker cables for whenever I do need it.

What do we have here?

I was reading about how to build a capacitor checker from the December 1959 issue of Popular Electronics and stumbled across something that looked very familiar.


I know that shape.


Nearly identical to a Bose® 901 Series I/II cabinet, and even specifically references expanding the sound field with a reflected wave. The 901 series uses what Bose calls “Direct/Reflecting” technology.

Anyone know about these “Cosmos Industries” speakers? Does anyone know any of their names, who might have gone on to work for the early Bose® corporation?