I built one from discrete transistors in a lab class in college, on a breadboard. Fun times debugging and getting it to work. Then I flashed an led with it right next to another led flashed from a 555 chip. With the same discrete timer caps, the flashing frequencies were different due to the extra parasitics in the breadboard discrete 555 version. So had to compensate the caps to make the flashes match each other's frequency.
That's a great exercise. The hard part is always that in chips you can pull stuff that is rather tricky discretely, for instance, a multi-emitter transistor. So you can't always do a 1:1 conversion but for a 555 it is still doable.
Only because odd components aren't marketable. There used to be 4-terminal MOSFETs, they weren't sold after ICs became normal. Never heard of a multi emitter transistor being sold discretely but it's possible.
When I was in college I was not in an engineering program but I was self-learning electronics. I was trying to learn to use a 555 timer to do something and couldn't get it to work.
So I went to the office hours of a random EE professor thinking they would help me out. Instead I got scolded about how 555 timers are not real engineering and that I shouldn't waste his time.
A little bit (scolding a beginner in this way is never acceptable), but I do feel like the 555 is really overrepresented in electronics learning materials. It's a quirky little chip, so learning about it doesn't really teach you much (most of the time it's just 'hook it up like so and it does this!', not 'here's how comparators and oscillators actually work'), and it's also now almost never the best or even a good solution for any of the problems it solves.
I used to salvage components from electronic stuff and was always looking out for 555s but never found any, in a whole range of vintages from 1970's to 2000's. I ended up with the same conclusion - it seemed to be a hobbyist's chip that real consumer products didn't use and felt amateurish for some reason I didn't understand.
The big problem I ran into playing around with 555s was that capacitors are very rarely the capacitance they claim. Unless you're speccing an expensive capacitor, you'll find your time constant varies quite a bit across devices and temperature. That's fine for some use cases, but completely a deal breaker for others.
That's funny because I have two objects on my desk for which I know that they use 555s. One is a no-name joystick with "autofire" function from the late 1980's. The other is a mass produced motor controller from the 2000's where the 555 generates the PWM signal for a FET.
That is a terrible learning environment. Our profs always leave a box outside the laboratory with free expired textbooks, partial part lots, and damaged/old test equipment.
Some people get into Science, Software, and Electronics for the wrong reasons.. And end up miserable teaching after failing in the private sector.
A few 555 can teach people a lot, and burning out parts is part of the learning process. Most fold the DIP legs under like a "dead bug", as that is the tradition to prevent its accidental re-use.
In terms of component cost, ATTINY or PIC10 mcu have internal RC oscillators with configurable PWM pin hardware. Thus a single component is usually better than the accumulated precision error in discreet parts around a 555.
I usually recommend an RC car/truck build, https://eater.net/6502 , and or an LDOmotors Voron kit. Getting your Ham Radio technician license will also introduce you to an intuitive understanding of EE component model limits.
This covers a lot about discreet analog circuits, and I recommend trying to figure out how every circuit works on your own:
The 555 figured prominently in a digital circuits course I took back in the mid-80s. It was into its second decade of existence by that point, and it's still going strong.
I designed the electronics for a heavy-duty industrial 3D printer and used a 555 in the failsafe circuit (alongside the manual e-stop). If it didn't get reset by a heartbeat from the embedded computer/software, it would unpower the heaters and actuators.
The 555 is a versatile little thing. I used it at university for a simple circuit which allowed an arduino to cut it’s own power for 5 minutes and then boot again.
Do it. Build a couple, then build a simple opamp mixer (it's a single opamp and a handful of resistors, and a couple of capacitors across the power supply), and then - get adventurous - a PT2399 delay kit.
Then take a look on https://yusynth.net at some of the VCF designs, and build one of them.
You won't have a synthesizer, you'll have some crazy homebrew drone machine that you can make scary movie sountracks with.
The late Harold DuBose of Spectra-Physics, repeatedly used 555's as power inverters in the electronic design of a frequency stabilized ring dye laser. He liked the strength of the output transistor.
Obviously TFA is satire/tongue in cheek and while you can do all sorts of awesome stuff with a 555 you can't patch those implementations without physically rewiring them which in many cases means throwing out the board and fabbing a new one, whereas a microcontroller-based board can often be fixed with a simple jtag debugger.
So, yeah, 555 timers are cool and doing things with analog ICs is groovy but there's a reason everyone just stuffs a small microcontroller in places where we used to just stuff a 555, and it's maintainability.
Two thoughts on situations where the 555 may be preferable, if anyone has experience how these compare :
1. Low-noise applications. I’d naively expect the 555 to be less noisy than a clocked digital microcontroller, though it’s been awhile since I’ve worked in this space.
2. Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
> Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
The 555 is very power hungry compared to a typical cheap low-power microcontroller. IIRC there are lower power variants but the 555 still fundamentally does timing by draining current through a resistor, which is going to result in losses.
> I’d naively expect the 555 to be less noisy than a clocked digital microcontroller
TTL ones were exceptionally noisy because the output transistors "shot through" - both output transistors would conduct for a moment shorting the supply rail to ground and crowbarring ridiculous interference onto other parts of the circuit.
and it comes with new set of problems: Now you need a FW guys to write and maintain software for it, then your hardware team may need to wait that FW guy to release software to test, or the FW guy need to wait hardware to test his software, etc.
Then in production, you need another stage to flash the FW, which add time and complexity.
Then security, cheap MCU usually has bad software protection, that means your software can be read out easily, not a big deal since the FW replacing the 555 would be dead simple anyway, but try to explain it to a non-technical CEO when he read about it on his morning's newspaper.
I built one from discrete transistors in a lab class in college, on a breadboard. Fun times debugging and getting it to work. Then I flashed an led with it right next to another led flashed from a 555 chip. With the same discrete timer caps, the flashing frequencies were different due to the extra parasitics in the breadboard discrete 555 version. So had to compensate the caps to make the flashes match each other's frequency.
That's a great exercise. The hard part is always that in chips you can pull stuff that is rather tricky discretely, for instance, a multi-emitter transistor. So you can't always do a 1:1 conversion but for a 555 it is still doable.
I saw this a while ago:
https://www.instructables.com/Designing-a-555-Timer-on-Discr...
Only because odd components aren't marketable. There used to be 4-terminal MOSFETs, they weren't sold after ICs became normal. Never heard of a multi emitter transistor being sold discretely but it's possible.
4 replies →
Do you still have a video saved somewhere?
When I was in college I was not in an engineering program but I was self-learning electronics. I was trying to learn to use a 555 timer to do something and couldn't get it to work.
So I went to the office hours of a random EE professor thinking they would help me out. Instead I got scolded about how 555 timers are not real engineering and that I shouldn't waste his time.
I never used a 555 timer ever since.
What a spectacular failure of education.
A little bit (scolding a beginner in this way is never acceptable), but I do feel like the 555 is really overrepresented in electronics learning materials. It's a quirky little chip, so learning about it doesn't really teach you much (most of the time it's just 'hook it up like so and it does this!', not 'here's how comparators and oscillators actually work'), and it's also now almost never the best or even a good solution for any of the problems it solves.
2 replies →
I used to salvage components from electronic stuff and was always looking out for 555s but never found any, in a whole range of vintages from 1970's to 2000's. I ended up with the same conclusion - it seemed to be a hobbyist's chip that real consumer products didn't use and felt amateurish for some reason I didn't understand.
The big problem I ran into playing around with 555s was that capacitors are very rarely the capacitance they claim. Unless you're speccing an expensive capacitor, you'll find your time constant varies quite a bit across devices and temperature. That's fine for some use cases, but completely a deal breaker for others.
That's funny because I have two objects on my desk for which I know that they use 555s. One is a no-name joystick with "autofire" function from the late 1980's. The other is a mass produced motor controller from the 2000's where the 555 generates the PWM signal for a FET.
How hilariously transparent that he didn’t know how to use a 555 and didn’t want to admit it.
That is a terrible learning environment. Our profs always leave a box outside the laboratory with free expired textbooks, partial part lots, and damaged/old test equipment.
Some people get into Science, Software, and Electronics for the wrong reasons.. And end up miserable teaching after failing in the private sector.
A few 555 can teach people a lot, and burning out parts is part of the learning process. Most fold the DIP legs under like a "dead bug", as that is the tradition to prevent its accidental re-use.
In terms of component cost, ATTINY or PIC10 mcu have internal RC oscillators with configurable PWM pin hardware. Thus a single component is usually better than the accumulated precision error in discreet parts around a 555.
I usually recommend an RC car/truck build, https://eater.net/6502 , and or an LDOmotors Voron kit. Getting your Ham Radio technician license will also introduce you to an intuitive understanding of EE component model limits.
This covers a lot about discreet analog circuits, and I recommend trying to figure out how every circuit works on your own:
https://archive.org/details/encyclopediaofelectroniccircuits...
Simulators are not perfect, but they are a lot cheaper when starting out. =3
Tutorials:
https://www.youtube.com/@FesZElectronics/videos
Tools:
https://www.analog.com/en/resources/design-tools-and-calcula...
https://web.archive.org/web/20200218212700/http://spectrum-s...
This requires a GPU on Windows, but is a more advanced newer Spice simulator:
https://www.qorvo.com/design-hub/design-tools/interactive/qs...
That’s why the Beach Boys made a song about the 409, the predecessor chip.
The 555 figured prominently in a digital circuits course I took back in the mid-80s. It was into its second decade of existence by that point, and it's still going strong.
I designed the electronics for a heavy-duty industrial 3D printer and used a 555 in the failsafe circuit (alongside the manual e-stop). If it didn't get reset by a heartbeat from the embedded computer/software, it would unpower the heaters and actuators.
In the same voice as saying that some language is Turing complete, we can now say that an electronic component is 555 complete.
The 555 is a versatile little thing. I used it at university for a simple circuit which allowed an arduino to cut it’s own power for 5 minutes and then boot again.
:) that is actually pretty cool!
Have to love the tone of the article.
I want to build an atari punk console with a 555 to learn basic soldering and electronics, fun stuff
Definitely do it.
Obligatory link to Forest Mims' book: https://archive.org/details/555-designs
Ah man I had that one. Total flashback when I opened your link. Thanks
Do it. Build a couple, then build a simple opamp mixer (it's a single opamp and a handful of resistors, and a couple of capacitors across the power supply), and then - get adventurous - a PT2399 delay kit.
Then take a look on https://yusynth.net at some of the VCF designs, and build one of them.
You won't have a synthesizer, you'll have some crazy homebrew drone machine that you can make scary movie sountracks with.
The late Harold DuBose of Spectra-Physics, repeatedly used 555's as power inverters in the electronic design of a frequency stabilized ring dye laser. He liked the strength of the output transistor.
Obligatory
https://youtu.be/mDhNQPt8An0?si=VlzHWK4Cxcxn9pSK
Obviously TFA is satire/tongue in cheek and while you can do all sorts of awesome stuff with a 555 you can't patch those implementations without physically rewiring them which in many cases means throwing out the board and fabbing a new one, whereas a microcontroller-based board can often be fixed with a simple jtag debugger.
So, yeah, 555 timers are cool and doing things with analog ICs is groovy but there's a reason everyone just stuffs a small microcontroller in places where we used to just stuff a 555, and it's maintainability.
Two thoughts on situations where the 555 may be preferable, if anyone has experience how these compare :
1. Low-noise applications. I’d naively expect the 555 to be less noisy than a clocked digital microcontroller, though it’s been awhile since I’ve worked in this space.
2. Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
> Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?
The 555 is very power hungry compared to a typical cheap low-power microcontroller. IIRC there are lower power variants but the 555 still fundamentally does timing by draining current through a resistor, which is going to result in losses.
A micro is far superior on both these metrics.
> I’d naively expect the 555 to be less noisy than a clocked digital microcontroller
TTL ones were exceptionally noisy because the output transistors "shot through" - both output transistors would conduct for a moment shorting the supply rail to ground and crowbarring ridiculous interference onto other parts of the circuit.
And price. A PY32 is about $0.08 in quantity and can do a lot more than a 555 - which is at least 3 times more expensive...
Puya? First time I hear of these things .. (having used ESP32, RPI Pico, Nordic and STM). Googling led me to OpenPuya https://py32.org/en/
and it comes with new set of problems: Now you need a FW guys to write and maintain software for it, then your hardware team may need to wait that FW guy to release software to test, or the FW guy need to wait hardware to test his software, etc.
Then in production, you need another stage to flash the FW, which add time and complexity.
Then security, cheap MCU usually has bad software protection, that means your software can be read out easily, not a big deal since the FW replacing the 555 would be dead simple anyway, but try to explain it to a non-technical CEO when he read about it on his morning's newspaper.