Hi Hagrid :) (Sorry I don't know your name). I start following your channel and came-up with your question about RL for TI 555. I'm Electronic Design and I usually reach out OEMs for technical support, so that's what I did xD I have use SA555 as the timer reference. Here is their feedback: "It seems to be a pull-up since its tied to Vcc. But RL improves VOH, but it is not required for TTL compatibility. " "It helps with the level of VOH but not the current. Here are the additional information that I have: 1) The bi-polar [NE,NA,SE,SA] 555 timers have a NPN emitter source output so RL can help VOH level in some cases. 2) The CMOS version of [LMC,TLC] 555 timers have CMOS drain outputs so full VCC and GND will be at output at light or no load. Therefore no RL is needed."
The discharge pin is the open-collector output, though. I can see in the datasheet that output is described as a buffer, but it's supposed to be a push-pull output stage. And if it were open-collector and the resistor weren't used, then it would be a high-impedance output half the time rather than giving two different voltages. If what you're saying is true, then there's something I'm not understanding about this.
From what I understand, the RL acts as a pull up resistor of sorts? But instead of pulling up a floating value, it pulls up the signal to 5 volts maybe? Just intuition.
You can make a 50% duty cycle astable multivibrator with a 555 timer which is even less complex as the standard circuit from the data sheet. You just need to control the capacitor across a resistor from the output pin 3. In fact I really don't know, why the data sheet recomments your circuit as it is more complex and it has disadvantages.
I have a question for you Simply Put. I want to control a few items sequentially. One to four items with a rating of 120 volts and 15 amperes. So I want to turn one on for one second and then another for one second then another one second and finally one more one second. But only one at a time with up to four items. How would I be able to do that Sir ??? Thanks
NICE VIDEO!! But I was expecting an adjustable freq square wave (50% duty cycle)...been looking for one a long time on 555. You're actually showing general "pulse trains".
A friend of mine wants to be able to dim some led lights she has going up her stairs in her house , they are very bright I think they were originally for tree outside. But I was going to use a 555 and a mosfet as a PWM but I'm not sure yet if they are using AC with a cap dropper or DC for power. Any tips?? my main concern is if it has large votage. Can I drop the voltage with a voltage divider to supply the 555?? And help would be appreciated👍
You'll have to examine the device very carefully to try to find anywhere that a transformer can be. If you can't find a transformer, even a tiny one (and they can be tiny), then you probably should assume it's a cap dropper and messing with that is incredibly dangerous. You could always cut off the power plug and get some other sort of ac-to-dc power supply and solder it onto that, of course, but at that point it would probably be cheaper and easier to buy other lights. You can definitely use a voltage divider to supply the 555, but you have to make sure your resistors can handle the power flowing through them. If they can't, then put additional ones in series or parallel to give the same overall resistance but splitting the power over multiple. For something like LED lights and low-frequency PWM (anything above 60Hz is probably fine, 150-200 Hz I guarantee is fine), really you don't need to worry about the subtle details like noise or loading the voltage divider. All you have to worry about is not interacting with mains voltage.
@@simplyput2796 thanks for the info. Yes i was thinking of using a different supply if it is a cap dropper!! not going to mess with mains. And il make sure to use beefy resistors if need have a good grasp in ohms law and power dissipation. So thank you again that helped alot just to know I'm on the right track👍
What happens when you short THRES and TRIG to GND or Vcc? can you build a monostable and astable 555 Timer config with just one chip? EDIT: i meant astable not bistable
Shorting either pin to either rail will result in the chip either getting stuck in an output state or entering an invalid state. It might or might not give goofy behaviour, but it will definitely not give useful behaviour. And if you want to do it in one chip, get the 556 which is just two 555s in one chip.
Actually it will give you a usefull result. If you pull pin 2 to either rail maybe trough 1k resistors it will discharge or charge the capacitor really fast (and Holding it either way) resulting in the output either high or low. Diconecting pin 2 (and 6) will return to "normal" astable mode. Also my second question wasnt if you can do both in parallel but if you could switch between them without editing the crcuit
So you're just trying to short TRIG or THRES as a sort of reset/disable? I mean, sure, but I don't see how that's useful considering there already is a RESET pin, and I don't see what benefit there is to fast-[dis]charging the capacitor since the capacitor is the timing element in the first place. As to your second part, you could just put each output through an AND gate where one input of each AND gate is an enable signal, and then join the outputs, so you just select the output by enabling one AND gate.
For debouncing an input, have you considered buying chips that have schmitt triggers on their inputs? Because that's basically what that's for, and most chip families have options with them. Although I'm not sure what debouncing and oscillation have to do with each other.
I never really understood why there is a 10nf capacitor on the control pin. This is much clearer now. Thanks!
Good material. Simple yet informative
This was the best explanation I've seen, thanks!
great explanation as usual,thank you.
Thanks for your great Videos!
I like your headphones
brilliant explanation. thank
Hi Hagrid :) (Sorry I don't know your name).
I start following your channel and came-up with your question about RL for TI 555.
I'm Electronic Design and I usually reach out OEMs for technical support, so that's what I did xD
I have use SA555 as the timer reference. Here is their feedback:
"It seems to be a pull-up since its tied to Vcc. But RL improves VOH, but it is not required for TTL compatibility.
"
"It helps with the level of VOH but not the current. Here are the additional information that I have:
1) The bi-polar [NE,NA,SE,SA] 555 timers have a NPN emitter source output so RL can help VOH level in some cases.
2) The CMOS version of [LMC,TLC] 555 timers have CMOS drain outputs so full VCC and GND will be at output at light or no load. Therefore no RL is needed."
Interesting stuff. A pity they don't bother to put such information in the datasheet in the first place.
The resistance connected between vcc and output is a dc bias resistance for open collector buffer.
The discharge pin is the open-collector output, though. I can see in the datasheet that output is described as a buffer, but it's supposed to be a push-pull output stage. And if it were open-collector and the resistor weren't used, then it would be a high-impedance output half the time rather than giving two different voltages. If what you're saying is true, then there's something I'm not understanding about this.
From what I understand, the RL acts as a pull up resistor of sorts? But instead of pulling up a floating value, it pulls up the signal to 5 volts maybe? Just intuition.
What if we put a power transistor and amplify discharge to handle smaller resistor ?
You can make a 50% duty cycle astable multivibrator with a 555 timer which is even less complex as the standard circuit from the data sheet. You just need to control the capacitor across a resistor from the output pin 3. In fact I really don't know, why the data sheet recomments your circuit as it is more complex and it has disadvantages.
I have a question for you Simply Put. I want to control a few items sequentially. One to four items with a rating of 120 volts and 15 amperes. So I want to turn one on for one second and then another for one second then another one second and finally one more one second. But only one at a time with up to four items. How would I be able to do that Sir ??? Thanks
NICE VIDEO!! But I was expecting an adjustable freq square wave (50% duty cycle)...been looking for one a long time on 555. You're actually showing general "pulse trains".
0:05 I see what you did there.
good stuff. miss your content.hope you are ok.
A friend of mine wants to be able to dim some led lights she has going up her stairs in her house , they are very bright I think they were originally for tree outside. But I was going to use a 555 and a mosfet as a PWM but I'm not sure yet if they are using AC with a cap dropper or DC for power. Any tips?? my main concern is if it has large votage. Can I drop the voltage with a voltage divider to supply the 555?? And help would be appreciated👍
You'll have to examine the device very carefully to try to find anywhere that a transformer can be. If you can't find a transformer, even a tiny one (and they can be tiny), then you probably should assume it's a cap dropper and messing with that is incredibly dangerous. You could always cut off the power plug and get some other sort of ac-to-dc power supply and solder it onto that, of course, but at that point it would probably be cheaper and easier to buy other lights.
You can definitely use a voltage divider to supply the 555, but you have to make sure your resistors can handle the power flowing through them. If they can't, then put additional ones in series or parallel to give the same overall resistance but splitting the power over multiple. For something like LED lights and low-frequency PWM (anything above 60Hz is probably fine, 150-200 Hz I guarantee is fine), really you don't need to worry about the subtle details like noise or loading the voltage divider. All you have to worry about is not interacting with mains voltage.
@@simplyput2796 thanks for the info. Yes i was thinking of using a different supply if it is a cap dropper!! not going to mess with mains. And il make sure to use beefy resistors if need have a good grasp in ohms law and power dissipation. So thank you again that helped alot just to know I'm on the right track👍
Upsides and downsides. I see what you did there.
What happens when you short THRES and TRIG to GND or Vcc?
can you build a monostable and astable 555 Timer config with just one chip?
EDIT: i meant astable not bistable
Shorting either pin to either rail will result in the chip either getting stuck in an output state or entering an invalid state. It might or might not give goofy behaviour, but it will definitely not give useful behaviour. And if you want to do it in one chip, get the 556 which is just two 555s in one chip.
Actually it will give you a usefull result. If you pull pin 2 to either rail maybe trough 1k resistors it will discharge or charge the capacitor really fast (and Holding it either way) resulting in the output either high or low. Diconecting pin 2 (and 6) will return to "normal" astable mode.
Also my second question wasnt if you can do both in parallel but if you could switch between them without editing the crcuit
So you're just trying to short TRIG or THRES as a sort of reset/disable? I mean, sure, but I don't see how that's useful considering there already is a RESET pin, and I don't see what benefit there is to fast-[dis]charging the capacitor since the capacitor is the timing element in the first place. As to your second part, you could just put each output through an AND gate where one input of each AND gate is an enable signal, and then join the outputs, so you just select the output by enabling one AND gate.
I am trying to reduce chip count, while also debouncing the input in the process.
Basically an astable oscillator, that can be single stepped at will.
For debouncing an input, have you considered buying chips that have schmitt triggers on their inputs? Because that's basically what that's for, and most chip families have options with them. Although I'm not sure what debouncing and oscillation have to do with each other.
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