I'm retired, and just learning electronics because it was always something that piqued my curiosity but never had the opportunity to explore it while working and maintain my other interests. Some things I know, most things I can use a fresh pair of eyes; this channel has given me the opportunity to re-examine some of the things I've learned. I've been enjoying the series so far. Thank you. Take care.
It's interesting to see a video on TH-cam in 2024 talking about the 555 timer. That chip is about 50 years old! But still very useful. It's also good for switch debouncing.
Just in case no one talked about it in the comments... the pin 5 capacitor would help sending to ground any high frqcy noises entering along with the vcc power to the 555. Other than that, the pin 5 role is to give another comparison voltage vs the threshold (pin6) instead of the default 2/3 vcc. Hope this makes sense. Note: the thing is that the pin 6 and 2 are not triggering the output high/low change upon vcc or 0V. the trigger pin 6, toggles the output on 2/3VCC (insteaf of VCC) and pin2 toggles the output on 1/3VCC (instead of 0V) Great channel 👍
It's cool how you're following a tutorial that we at home can also try, but with the added benefit that we can see each step as you do it. Thanks for this really valuable resource!
Loving your vids. I love the way you talk through the process and say your logic out loud. I don't think that enough people do that and I feel like it's just good for everybody. Also diode steering is a way to get a perfect 50/50 but it does add a few components but realistically most of the time of true 50/50 is not needed at all but I also feel the need to keep saying symmetrical where possible LOL
There are diagrams of the internals of the 555 available. It consists of an s-r flipflop with the set driven by one of two comparators and reset by the other. There are three internal series resistors with connections to the comparators at 1/3 and 2/3. Study this along with the circuit description and equations describing voltage vs. time for RC circuits and operation of the 555 will become much clearer to you.
Here's a really simple clock generator circuit: Use the Schmitt trigger device you used for switch debounce. Connect a resistor from its input to its output. Since you are using LS TTL a resistor of around 500 ohms is about the maximum. Connect a capacitor from the input to ground. Instant oscillator! Unless you use a large cap you'll need your logic probe to confirm it is oscillating (probe will light up with HIGH and LOW; if it has a pulse detector that may flash). This isn't a particularly good circuit because variation from part to part can be fairly large and the low value resistor means you need a big cap for low frequency. With a CMOS schmitt you can use very much high resistor values.
On of the downsides of 555 is the inability to regulate PWM (the symetry of the square) down to 0, it's 50-100% Thic can be fixed with taking the output out of capacitor and using extra op-amp to form the square wave. Pin 5 is used to raise the threshold level effectively changing the output frequency. Put there square wave - you'll have dual tone output, put sine wave - a siren, sawtooth - a frequency sweep. Have a look at the internal wiring of 555 (the functional blocks) things will make more sense. 555 can be also used in one-shoot configuratiion and used for debouncing side note: Since you already have your shmitt gates out you don't need 555 at all. Due to having the hysteresis these gates (NOT/NAND/NOR) can be used to generate square wave with just an extra capacitor and resistor. Also if you don't have an oscilloscope you can use a sound card and a simple probe. There's comprehensive software for it as well. It's only up to 44kHz but I feel that's enough for your needs.
There is no reliable way to get exactly 50% duty cycle with a 555. There are ways to get a reasonable approximation, but that's the best you can hope for. With a CMOS version that isn't driving any other significant load you can get quite good results by using a single resistor between the output and the timing capacitor with no other timing resistors. This relies on the fact that with the CMOS part the output will swing from very close to Vdd (postive) to very close to ground. It doesn't work well with the standard bipolar part because its output cant swing all the way to the positive supply. In general if you need precisely 50% duty cycle (a true "square" wave with equal HIGH and LOW times) you start with a clock that is twice the frequency you require and divide it by two with a flip-flop. That way each half cycle is equal to the full period of the input clock. You don't need a 50% duty cycle to clock your counter circuit. If you were pushing the counter the maximum frequency it can handle a 50% duty cycle _might_ be necessary to meet the requirements for LOW and HIGH times. The cap on pin 5 is, as the document said, to filter noise. There are three nominally 5k resistors in series between the positive supply pin of the 555 and its ground pin. These set voltages of 2/3 of Vcc and 1/3 of Vcc. When the cap is charging, the 555 "turns over" when the cap voltage reaches the 2/3 reference. Discharging then continues until the cap is discharged down to the the 1/3 reference. If there is high frequency noise on those references then either a charge or discharge period can be cut short or lengthened. Power supply rails in digital circuity tend to be noisy (and in fact the bipolar 555 is absolutely horrible for making the supply noisy!). The capacitor acts as a "low pass filter" to remove at least some of the high frequency noise that may be present. The discharge pin is "open collector." It is connected to the collector of transistor that has its emitter connected to ground. When that transistor is turned on current can flow into discharge pin. As long as the current is moderate (a few tens of milliamps) the voltage will swing to within 100 mV of ground (see TI datasheet for graph). If the transistor is off, current (ignoring "leakage" of typically nanoamperes to a few µA) flows neither into nor out of the discharge pin. Typically with a 555 astable it is best to use resistors of no less than a few hundred ohms. If you want to try to get 50% duty cycle, use perhaps 470 to 1000 ohms as the resistor to supply, make the other resistor much larger and choose the capacitor value to get the frequency you want. Read the TI datasheet for the LM555. Learning enough to understand it will help you with lots of common things that arise in real-world circuits. also see the LMC555 datasheet for a CMOS version
Yyou don't need 9V, you need to read the datasheet:. With the part number "NE555P" and the manufacturer "Texsas Instruments" you search the datasheet for the specific chip that you have, inside it you'll find in something like "Recommended Operating Conditions"which tells us that it operates with a "Vcc Suply voltage" from 4.5 to 16V. the "P" at the end tells you the type of package "PDIP". To give you another example "LMC555" works from 1.5 to 15 V
I keep wondering if you're planning to get that oscilloscope. On the one hand, it would be a big aid in troubleshooting, but at the same time it would change the style of how you are puzzling things out. There was a really good recent exploration of the 555's inner workings by IMSAI Guy: th-cam.com/video/r_cZVAUx2Os/w-d-xo.htmlsi=3iHjnEZ71PNJAjMt
I know there are relatively inexpensive ones, but they've always seemed like such a big and specialized piece of equipment and I'm a bit hesitant to take the leap because it'd be "serious!" Another consideration is my filming setup - I only have my phone for a camera in my top-down rig, so it might be hard to see an oscilloscope screen at that angle. I worry that getting one might bring a host of secondary complications along those lines. I don't have the money for multiple cameras to try to get additional angles or whatever, either, so... yeah. Dunno. Maybe if someday I make any money with these perhaps it'll justify it! In the meantime I'm more worried about not knowing what to do next and running out of ideas/skill well before that might happen. 😛
Yeah, that makes sense. I happened to catch an introductory deal on a very fancy oscilloscope a few years ago that took it from "way out of my budget" down to merely "extravagant and ill-advised" territory. If I amortize the cost over the 5 times I've used it... that doesn't help justify it at all. But one of the cool features for making videos is that it has a web interface that serves up a real-time view of what's on the screen and front panel, so it's super easy to screen record. (I fawned over it in th-cam.com/video/Nd2Sb_5vJF8/w-d-xo.htmlsi=9TeKovw2jN_tXWtD) Anyway, that was quite a few years ago, and I don't know if it's common to have a web UI like that, but a lot of them have HDMI out now. There's also the option of something like an Analog Discovery that you plug into your computer and get a whole bunch of instruments for a few hundred bucks.
Hmmm.. I didn't consider they might have something like HDMI or some other output options. That could indeed be pretty handy! I know some TH-camrs use what appear to be software scopes - I think they're just a box with probes and the computer does all the work. (Although they often seem to struggle with them so I wonder if they're very good?) I think I'd probably rather have a physical one with actual buttons and knobs and stuff, anyway. I'll have to keep the video/web output feature possibility in mind if I ever get to that point!
![BOWKYLION - วิงวอน (ex-change) [Official MV]](http://i.ytimg.com/vi/cLdnZWDaO-w/mqdefault.jpg)
I'm retired, and just learning electronics because it was always something that piqued my curiosity but never had the opportunity to explore it while working and maintain my other interests. Some things I know, most things I can use a fresh pair of eyes; this channel has given me the opportunity to re-examine some of the things I've learned. I've been enjoying the series so far. Thank you. Take care.
It's interesting to see a video on TH-cam in 2024 talking about the 555 timer.
That chip is about 50 years old! But still very useful. It's also good for switch debouncing.
Just in case no one talked about it in the comments... the pin 5 capacitor would help sending to ground any high frqcy noises entering along with the vcc power to the 555. Other than that, the pin 5 role is to give another comparison voltage vs the threshold (pin6) instead of the default 2/3 vcc. Hope this makes sense.
Note: the thing is that the pin 6 and 2 are not triggering the output high/low change upon vcc or 0V. the trigger pin 6, toggles the output on 2/3VCC (insteaf of VCC) and pin2 toggles the output on 1/3VCC (instead of 0V)
Great channel 👍
It's cool how you're following a tutorial that we at home can also try, but with the added benefit that we can see each step as you do it. Thanks for this really valuable resource!
These get better and better! And I’m learning something! Way to go Sean!
I learned a lot, great stuff man.
I like these types of videos!
Loving your vids. I love the way you talk through the process and say your logic out loud. I don't think that enough people do that and I feel like it's just good for everybody. Also diode steering is a way to get a perfect 50/50 but it does add a few components but realistically most of the time of true 50/50 is not needed at all but I also feel the need to keep saying symmetrical where possible LOL
There are diagrams of the internals of the 555 available. It consists of an s-r flipflop with the set driven by one of two comparators and reset by the other. There are three internal series resistors with connections to the comparators at 1/3 and 2/3. Study this along with the circuit description and equations describing voltage vs. time for RC circuits and operation of the 555 will become much clearer to you.
Here's a really simple clock generator circuit:
Use the Schmitt trigger device you used for switch debounce. Connect a resistor from its input to its output. Since you are using LS TTL a resistor of around 500 ohms is about the maximum. Connect a capacitor from the input to ground. Instant oscillator! Unless you use a large cap you'll need your logic probe to confirm it is oscillating (probe will light up with HIGH and LOW; if it has a pulse detector that may flash).
This isn't a particularly good circuit because variation from part to part can be fairly large and the low value resistor means you need a big cap for low frequency. With a CMOS schmitt you can use very much high resistor values.
Dronebot workshop "using the 555 timer" is an excellent description of how it works.
On of the downsides of 555 is the inability to regulate PWM (the symetry of the square) down to 0, it's 50-100% Thic can be fixed with taking the output out of capacitor and using extra op-amp to form the square wave.
Pin 5 is used to raise the threshold level effectively changing the output frequency. Put there square wave - you'll have dual tone output, put sine wave - a siren, sawtooth - a frequency sweep. Have a look at the internal wiring of 555 (the functional blocks) things will make more sense.
555 can be also used in one-shoot configuratiion and used for debouncing
side note: Since you already have your shmitt gates out you don't need 555 at all. Due to having the hysteresis these gates (NOT/NAND/NOR) can be used to generate square wave with just an extra capacitor and resistor.
Also if you don't have an oscilloscope you can use a sound card and a simple probe. There's comprehensive software for it as well. It's only up to 44kHz but I feel that's enough for your needs.
If you still want to know about 555 timer .. watch diode gone wild on 555 timer . He does a great explanation on depth about.. from the basics
Incidentally you can use a 555 in Mono-stable mode to debounce a button press!
👌👌
There is no reliable way to get exactly 50% duty cycle with a 555. There are ways to get a reasonable approximation, but that's the best you can hope for. With a CMOS version that isn't driving any other significant load you can get quite good results by using a single resistor between the output and the timing capacitor with no other timing resistors. This relies on the fact that with the CMOS part the output will swing from very close to Vdd (postive) to very close to ground. It doesn't work well with the standard bipolar part because its output cant swing all the way to the positive supply.
In general if you need precisely 50% duty cycle (a true "square" wave with equal HIGH and LOW times) you start with a clock that is twice the frequency you require and divide it by two with a flip-flop. That way each half cycle is equal to the full period of the input clock. You don't need a 50% duty cycle to clock your counter circuit. If you were pushing the counter the maximum frequency it can handle a 50% duty cycle _might_ be necessary to meet the requirements for LOW and HIGH times.
The cap on pin 5 is, as the document said, to filter noise. There are three nominally 5k resistors in series between the positive supply pin of the 555 and its ground pin. These set voltages of 2/3 of Vcc and 1/3 of Vcc. When the cap is charging, the 555 "turns over" when the cap voltage reaches the 2/3 reference. Discharging then continues until the cap is discharged down to the the 1/3 reference. If there is high frequency noise on those references then either a charge or discharge period can be cut short or lengthened. Power supply rails in digital circuity tend to be noisy (and in fact the bipolar 555 is absolutely horrible for making the supply noisy!). The capacitor acts as a "low pass filter" to remove at least some of the high frequency noise that may be present.
The discharge pin is "open collector." It is connected to the collector of transistor that has its emitter connected to ground. When that transistor is turned on current can flow into discharge pin. As long as the current is moderate (a few tens of milliamps) the voltage will swing to within 100 mV of ground (see TI datasheet for graph). If the transistor is off, current (ignoring "leakage" of typically nanoamperes to a few µA) flows neither into nor out of the discharge pin.
Typically with a 555 astable it is best to use resistors of no less than a few hundred ohms. If you want to try to get 50% duty cycle, use perhaps 470 to 1000 ohms as the resistor to supply, make the other resistor much larger and choose the capacitor value to get the frequency you want.
Read the TI datasheet for the LM555. Learning enough to understand it will help you with lots of common things that arise in real-world circuits.
also see the LMC555 datasheet for a CMOS version
save yourself effort by reading the internal schematic on the datasheet. no guessing needed.
You need the auld 9V. The 5 - 5 - 5 part of the timer has meaning. if you look at the internals you will see why you need the 9v.
Yyou don't need 9V, you need to read the datasheet:.
With the part number "NE555P" and the manufacturer "Texsas Instruments" you search the datasheet for the specific chip that you have,
inside it you'll find in something like "Recommended Operating Conditions"which tells us that it operates with a "Vcc Suply voltage" from 4.5 to 16V.
the "P" at the end tells you the type of package "PDIP".
To give you another example "LMC555" works from 1.5 to 15 V
@@dgo85
Sorry my bad, I should have read the datasheet. I was sure the NE 555s were 6-12V,I was wrong.
I keep wondering if you're planning to get that oscilloscope. On the one hand, it would be a big aid in troubleshooting, but at the same time it would change the style of how you are puzzling things out.
There was a really good recent exploration of the 555's inner workings by IMSAI Guy: th-cam.com/video/r_cZVAUx2Os/w-d-xo.htmlsi=3iHjnEZ71PNJAjMt
I know there are relatively inexpensive ones, but they've always seemed like such a big and specialized piece of equipment and I'm a bit hesitant to take the leap because it'd be "serious!"
Another consideration is my filming setup - I only have my phone for a camera in my top-down rig, so it might be hard to see an oscilloscope screen at that angle. I worry that getting one might bring a host of secondary complications along those lines. I don't have the money for multiple cameras to try to get additional angles or whatever, either, so... yeah. Dunno. Maybe if someday I make any money with these perhaps it'll justify it! In the meantime I'm more worried about not knowing what to do next and running out of ideas/skill well before that might happen. 😛
Yeah, that makes sense. I happened to catch an introductory deal on a very fancy oscilloscope a few years ago that took it from "way out of my budget" down to merely "extravagant and ill-advised" territory. If I amortize the cost over the 5 times I've used it... that doesn't help justify it at all. But one of the cool features for making videos is that it has a web interface that serves up a real-time view of what's on the screen and front panel, so it's super easy to screen record. (I fawned over it in th-cam.com/video/Nd2Sb_5vJF8/w-d-xo.htmlsi=9TeKovw2jN_tXWtD)
Anyway, that was quite a few years ago, and I don't know if it's common to have a web UI like that, but a lot of them have HDMI out now. There's also the option of something like an Analog Discovery that you plug into your computer and get a whole bunch of instruments for a few hundred bucks.
Hmmm.. I didn't consider they might have something like HDMI or some other output options. That could indeed be pretty handy! I know some TH-camrs use what appear to be software scopes - I think they're just a box with probes and the computer does all the work. (Although they often seem to struggle with them so I wonder if they're very good?) I think I'd probably rather have a physical one with actual buttons and knobs and stuff, anyway. I'll have to keep the video/web output feature possibility in mind if I ever get to that point!
You can buy a Scope kit for about $30,00 which would be good for what you are doing.