555 internals circuit doesn't match 555 component

[woreno]

if using the 555 IC i cannot do the most simple circuit - monostable (one shot trigger). i was expecting a low-hi-low output when flipping the switch; also when the cap charges to 2/3 vcc i expected to go down (it won't). however, opening your 555 internal example (2 opamps + 2 nors +npn), and modifying the pins to the monostable circuit it works as it should maybe my bad?

---

monostable:

6. 7. threshold-discharge: shorted; between this node a resistor to vcc and capacitor to ground 4, 8. reset, vcc to 5V; 1. gnd
7. control don't care
8. trigger: connected to a pull up resistor to vcc; followed to a switch to ground won't make a signal low-hi-low by the 1.1RC..

this is the example with the IC:

$ 1 0.000005 5.023272298708815 64 7 50 5e-11 g 16 192 16 208 0 0 r 64 192 64 112 0 10000 R 304 32 272 32 0 0 40 5 0 0 0.5 O 352 160 416 160 0 0 165 176 96 192 96 6 4.999999950000001 w 240 64 304 64 0 w 304 64 304 128 0 w 352 160 304 160 0 w 64 192 112 192 0 g 272 256 272 272 0 0 w 304 64 304 32 0 s 64 192 16 192 0 0 false R 64 112 32 112 0 0 40 5 0 0 0.5 R 144 64 112 64 0 0 40 5 0 0 0.5 r 144 64 144 128 0 1000 w 160 128 176 128 0 c 144 240 144 272 0 0.00001 4.974491983331485 0.001 g 144 272 144 288 0 0 w 160 128 144 128 0 w 176 224 144 224 0 w 144 224 144 240 0 w 144 224 144 128 0 w 176 192 112 192 0 o 3 32 0 x83013 5 0.1 0 1 1.25 0 o 16 32 0 x83013 5 0.1 1 2 1.25 0 16 3 0.025 0

this is the same but using your internals example : $ 3 0.000005 5.023272298708815 64 7 50 5e-11 a 288 168 384 168 9 5 0 1000000 0 3.333333333333333 100000 a 288 264 384 264 9 5 0 1000000 6.666666666666666 9.703215267284776 100000 r 240 56 240 104 0 5000 r 240 104 240 152 0 5000 w 240 152 240 280 0 r 240 280 240 328 0 5000 w 240 152 288 152 0 w 240 104 272 104 0 w 272 104 272 280 0 w 272 280 288 280 0 w 464 176 464 192 0 w 384 184 384 192 0 w 384 192 464 240 0 w 464 240 464 256 0 w 384 240 384 248 0 w 384 240 464 192 0 R 240 56 240 16 0 0 40 10 0 0 0.5 R 56 56 56 24 0 0 40 10 0 0 0.5 r 56 56 56 120 0 1000 r -16 144 -16 208 0 10000 w 216 120 216 352 0 c 56 120 56 152 0 0.000009999999999999999 9.703215267284776 0.001 g 56 152 56 168 0 0 r 384 368 464 368 0 10000 w 464 176 496 176 0 w 464 368 496 368 0 153 384 256 464 256 1 2 0 5 153 384 176 464 176 1 2 0 5 w 496 176 496 368 0 O 464 256 544 256 0 0 t 328 368 296 368 0 1 -9.703215169252609 9.803216694199141e-8 100 default w 216 352 296 352 0 g 296 384 296 408 0 0 w 328 368 384 368 0 x 120 115 189 118 4 16 discharge x 131 173 176 176 4 16 trigger x 120 242 185 245 4 16 threshold w 272 104 272 32 0 x 272 22 320 25 4 16 control b 514 398 200 40 0 w 240 328 240 384 0 w 240 384 296 384 0 w 56 56 -16 56 0 w -16 144 -16 56 0 s -16 208 -72 208 0 0 false g -72 208 -72 224 0 0 w 56 120 120 120 0 w 120 120 120 248 0 w 288 248 120 248 0 w 216 120 120 120 0 w -16 208 200 208 0 w 288 184 200 184 0 w 200 184 200 200 0 w 200 200 200 208 0 o 21 16 0 4099 10 0.00625 0 2 21 3 o 29 32 0 4106 5 0.00009765625 1 1

[woreno]

btw, when copy-paste the internal 555 example to a new blank circuit, i could not connect to the wires (maybe due to the grid that was different) so i had to reinsert the components and set the values accordingly (im using chrome 96.0.4664.110 / 64bits/ windows)

[pfalstad]

Wikipedia says "As long as this pin [the Trigger pin] continues to be kept at a low voltage, the OUTPUT will remain in the high state." I have not doublechecked this against the 555 schematic though. My 555 internals is a simplified version; I'm not sure if the real 555 acts the same way. I can check against the transistor-level 555 schematic.

The circuit works if the switch is normally open. If you close it for a short interval, then you will get the monostable behavior.

[pfalstad]

The copy-paste problem is because the internal 555 example is using the small grid option. We should turn that option on if pasting something from a small grid circuit.

[pfalstad]

After looking at a better block diagram, and the full transistor-level schematic, I think it's a bug in the 555 internals circuit. The output is low but the discharge pin has no current. That shouldn't happen.

[woreno]

ok ok ! maybe my bad. i will look for that option then. great work.

[pfalstad]

I'll keep this open because I should fix the internals circuit. Its behavior should match the 555 component.

[woreno]

both seem ok now.. for sure it was me, just stuborn'ing flipping the switch low-hi-low instead the opposite hi-low-hi, then swichting between two diagrams.

one note, the D flipflop you can put reset/set inverted, but then, the IC drawing doesn't reflect if R/S is active to low or to hi i used to follow the 74 version, so maybe i don't know sorry so much for the time, great work.

[pfalstad]

Re the D flipflop, it shows a little bubble if R/S is active low

[woreno]

argh ok..forgive me

Paul Falstad @.***> escreveu no dia sexta, 17/12/2021 à(s) 21:32:

Re the D flipflop, it shows a little bubble if R/S is active low

— Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications on the go with GitHub Mobile for iOS or Android. You are receiving this because you modified the open/close state.Message ID: @.***>

-- Manuel Moreno @. @.