Hardly a week goes by that we don’t post a project where at least one commenter will lament that the hacker could have just used a 555. [Peter Monta] clearly gets that point of view. For a 555 design contest, he created both digital logic gates and an op amp, all using 555 chips. We can’t quite imagine the post apocalyptic world where the only surviving electronic components are 555 chips, but if that day were to come, [Peter] is your guy.
Using the internal structure of the 555, [Peter] formed a basic logic gate, an inverter, latches, and more. He also composed things like counters and seven-segment decoders. He had a very simple 4-bit CPU design in Verilog that he was going to attempt until he realized it would map into almost 400 chips (half of that if you’d use a dual 555, but still). If you built this successfully, we would probably post it, by the way. You can see a video of the digital logic counter, below.
The op amp, however, is a bit trickier. Each input (+ and -) have their own 555 chip. Another 555 generates a ramp, so essentially the input voltage converts to a time-based PWM signal. Some logic gates made using the 555 techniques and a pair of diodes generate pulses proportional to the difference between the signal. Finally, a capacitor integrates the output back to a voltage. If you lost count, that’s ten 555 chips to make a single op amp!
To test things out, [Peter] wired the circuit up as an inverting 10X amplifier. It worked but suffered from a few issues like noise in the output due to PWM artifacts and difficulty responding to square waves. Still, considering this is done with 555s, you have to cut some slack.
Practical? No, of course not. But it is interesting to see someone think out of the box and then try to imagine what you could do to bend a device to your will, just for the practice.
Commenters will no doubt enjoy pointing out that the logic could be done with an Arduino and there are plenty of op amp devices you can buy for next to nothing, many of which have multiple devices per package. But that really isn’t the point.
The last time we confused commenters, we saw a mix of 555 and an Arduino on the same circuit. As long as you are being impractical, you might as well go big. We thought about replicating the op amp using these giant discrete 555 “chips”.