Category Archives: Projects

TT555 Soldering Kit now available on Tindie!

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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!

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The TT555: a discrete 555 timer plug-in replacement

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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.

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The TT741: a discrete plug-in 741 replacement

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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?

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