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#1
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Specific 555 circuit
Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25
years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. Henry |
#2
Posted to alt.electronics
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Specific 555 circuit
On 2005-12-25, Henry wrote:
Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. if by retrigerable monostable you mean have it restart its timing interval while in the "on" state, no that can't be done using the 555 alone. the 555 operates by charging (or discharging) a capacitor. to restart the interval you'd have to arrange for the capacitor to be discharged back to its starting voltage. Bye. Jasen |
#3
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Specific 555 circuit
"Jasen Betts" wrote in message ... On 2005-12-25, Henry wrote: Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. if by retrigerable monostable you mean have it restart its timing interval while in the "on" state, no that can't be done using the 555 alone. the 555 operates by charging (or discharging) a capacitor. to restart the interval you'd have to arrange for the capacitor to be discharged back to its starting voltage. Bye. Jasen Okay, thanks. That foils my one idea. I have an old SN74123 Dual re-trigerable monostable multivibrator. I had simply hoped that a single 555 timer could do the same so that I did not have to waste half the 74123 package. I only have a couple of these and no funds to acquire anymore of them at the present. Henry |
#4
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Specific 555 circuit
On Sun, 25 Dec 2005 05:55:22 -0500, "Henry"
wrote: Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. --- Try this: (view in Courier) +V-----------------------+--------------+-------+ | | |8 [1K] [Rt] +---+---+ | | 2|_ Vcc |3 +--------------|--O|T OUT|-- OUT | | 6| | C +---|TH | IN-------+-[0.1µF]--+--B NPN | 7|_ 7555| | | E +-----+--O|D | | | | | +| | GND | | | | D [Ct] +---+---+ [10K] +-----------G NCH | |1 | | | S | | | [10K] | | | | | | | | | | GND-----+----------+----+--------+-----+-------+ The input is a positive-going pulse or edge. -- John Fields Professional Circuit Designer |
#5
Posted to alt.electronics
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Specific 555 circuit
"John Fields" wrote in message news On Sun, 25 Dec 2005 05:55:22 -0500, "Henry" wrote: Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. --- Try this: (view in Courier) +V-----------------------+--------------+-------+ | | |8 [1K] [Rt] +---+---+ | | 2|_ Vcc |3 +--------------|--O|T OUT|-- OUT | | 6| | C +---|TH | IN-------+-[0.1µF]--+--B NPN | 7|_ 7555| | | E +-----+--O|D | | | | | +| | GND | | | | D [Ct] +---+---+ [10K] +-----------G NCH | |1 | | | S | | | [10K] | | | | | | | | | | GND-----+----------+----+--------+-----+-------+ The input is a positive-going pulse or edge. -- John Fields Professional Circuit Designer Thanks, I will give it a try. One question. I am uncertain what the NCH component is. I assume its not hydrogen cyanide as that would be HCN. :-) Henry |
#6
Posted to alt.electronics
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Specific 555 circuit
On Mon, 26 Dec 2005 16:19:06 -0500, "Henry"
wrote: "John Fields" wrote in message news On Sun, 25 Dec 2005 05:55:22 -0500, "Henry" wrote: Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. --- Try this: (view in Courier) +V-----------------------+--------------+-------+ | | |8 [1K] [Rt] +---+---+ | | 2|_ Vcc |3 +--------------|--O|T OUT|-- OUT | | 6| | C +---|TH | IN-------+-[0.1µF]--+--B NPN | 7|_ 7555| | | E +-----+--O|D | | | | | +| | GND | | | | D [Ct] +---+---+ [10K] +-----------G NCH | |1 | | | S | | | [10K] | | | | | | | | | | GND-----+----------+----+--------+-----+-------+ The input is a positive-going pulse or edge. -- John Fields Professional Circuit Designer Thanks, I will give it a try. One question. I am uncertain what the NCH component is. I assume its not hydrogen cyanide as that would be HCN. :-) --- It's a nitrogen carbon hydride switch. Actually, it's an N-Channel enhancement mode MOSFET with a channel resistance which will discharge Ct sufficiently close to ground before the input pulse goes away so that you can predict the increased length of the output pulse. If you don't have any MOSFETS, an NPN transistor will work if Ct isn't too big. -- John Fields Professional Circuit Designer |
#7
Posted to alt.electronics
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Specific 555 circuit
On Mon, 26 Dec 2005 16:31:40 -0600, John Fields
wrote: On Mon, 26 Dec 2005 16:19:06 -0500, "Henry" wrote: "John Fields" wrote in message news On Sun, 25 Dec 2005 05:55:22 -0500, "Henry" wrote: Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25 years rusty since I tinkered with this stuff all those years ago. Anyway, working on a project where it would be deal to have a 555-timer based monostable multivibrator (with retrigger ability.) Is that possible with the 555? I have found many circuits online (actually mostly the same one over and over again) but they dont seem to support re-triggering with the 555. --- Try this: (view in Courier) +V-----------------------+--------------+-------+ | | |8 [1K] [Rt] +---+---+ | | 2|_ Vcc |3 +--------------|--O|T OUT|-- OUT | | 6| | C +---|TH | IN-------+-[0.1µF]--+--B NPN | 7|_ 7555| | | E +-----+--O|D | | | | | +| | GND | | | | D [Ct] +---+---+ [10K] +-----------G NCH | |1 | | | S | | | [10K] | | | | | | | | | | GND-----+----------+----+--------+-----+-------+ The input is a positive-going pulse or edge. -- John Fields Professional Circuit Designer Thanks, I will give it a try. One question. I am uncertain what the NCH component is. I assume its not hydrogen cyanide as that would be HCN. :-) --- It's a nitrogen carbon hydride switch. Actually, it's an N-Channel enhancement mode MOSFET with a channel resistance which will discharge Ct sufficiently close to ground before the input pulse goes away so that you can predict the increased length of the output pulse. If you don't have any MOSFETS, an NPN transistor will work if Ct isn't too big. --- Aarghhh!!! There's a gross error in the circuit which I'll fix tomorrow... Hint: Vbe of the NPN won't allow the MOSFET to turn on, duh... -- John Fields Professional Circuit Designer |
#8
Posted to alt.electronics
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Specific 555 circuit
On Mon, 26 Dec 2005 18:15:48 -0600, John Fields
wrote: Aarghhh!!! There's a gross error in the circuit which I'll fix tomorrow... Hint: Vbe of the NPN won't allow the MOSFET to turn on, duh... --- KISS works best... +V | +-------+ | |8 [Rt] +---+---+ | 2|_ Vcc |3 IN---+----------|--O|T OUT|-- OUT | | 6| | | +---|TH | [1000] | 7|_ 7555| | +-----+--O|D | | | +| | GND | | E [Ct] +---+---+ +--B PNP | |1 C | | | | | +-----+-------+ | GND Unlike the vanilla 7555 which starts timing out when pin 2 goes low, with the retrigger it starts timing out when pin 2 goes high. That means that pin 3 will be high for the timeout period (1.4RC) plus as long as pin 2 stays low: _ t = (1.4RC) + (tT) If you don't already have it you might want to download Linear's excellent simulator at: http://www.linear.com/company/software.jsp It's free, and you can use it to build stuff without having to buy parts, which might be handy for you in your present situation. Anyway, here's the netlist for the circuit above if you want to check it out: Version 4 SHEET 1 960 680 WIRE -432 352 -432 224 WIRE -432 528 -432 432 WIRE -256 336 -256 288 WIRE -256 528 -432 528 WIRE -256 528 -256 416 WIRE -144 224 -432 224 WIRE -144 432 -144 224 WIRE -80 352 -80 80 WIRE -16 528 -256 528 WIRE -16 528 -16 160 WIRE 48 160 -16 160 WIRE 48 224 -144 224 WIRE 48 288 -256 288 WIRE 48 352 -80 352 WIRE 64 432 -144 432 WIRE 272 432 144 432 WIRE 336 80 -80 80 WIRE 336 160 272 160 WIRE 336 160 336 80 WIRE 336 224 272 224 WIRE 336 288 272 288 WIRE 336 288 336 224 WIRE 336 320 336 288 WIRE 336 384 336 320 WIRE 336 528 -16 528 WIRE 336 528 336 480 WIRE 432 160 336 160 WIRE 432 192 432 160 WIRE 432 320 336 320 WIRE 432 320 432 272 WIRE 432 352 432 320 WIRE 432 528 336 528 WIRE 432 528 432 416 WIRE 656 160 432 160 WIRE 656 240 656 160 WIRE 656 528 432 528 WIRE 656 528 656 320 WIRE 656 576 656 528 FLAG 656 576 0 SYMBOL Misc\\NE555 160 256 R0 SYMATTR InstName U1 SYMBOL voltage -432 336 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(5 0 0 0 0 .1 .5 2) SYMATTR InstName V1 SYMBOL voltage 656 224 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR SpiceLine Rser=0 SYMATTR InstName V2 SYMATTR Value 5 SYMBOL res -272 320 R0 SYMATTR InstName R1 SYMATTR Value 1000 SYMBOL res 416 176 R0 SYMATTR InstName R2 SYMATTR Value 1e6 SYMBOL cap 416 352 R0 SYMATTR InstName C1 SYMATTR Value 1e-6 SYMBOL pnp 272 480 M180 SYMATTR InstName Q1 SYMATTR Value 2N4403 SYMBOL res 160 416 R90 WINDOW 0 63 58 VBottom 0 WINDOW 3 67 59 VTop 0 SYMATTR InstName R3 SYMATTR Value 1000 TEXT -354 616 Left 0 !.tran 0 5s 0 .001s -- John Fields Professional Circuit Designer |
#9
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Specific 555 circuit
On Tue, 27 Dec 2005 07:35:17 -0600, John Fields
wrote: On Mon, 26 Dec 2005 18:15:48 -0600, John Fields wrote: Aarghhh!!! There's a gross error in the circuit which I'll fix tomorrow... Hint: Vbe of the NPN won't allow the MOSFET to turn on, duh... --- KISS works best... +V | +-------+ | |8 [Rt] +---+---+ | 2|_ Vcc |3 IN---+----------|--O|T OUT|-- OUT | | 6| | | +---|TH | [1000] | 7|_ 7555| | +-----+--O|D | | | +| | GND | | E [Ct] +---+---+ +--B PNP | |1 C | | | | | +-----+-------+ | GND Unlike the vanilla 7555 which starts timing out when pin 2 goes low, with the retrigger it starts timing out when pin 2 goes high. That means that pin 3 will be high for the timeout period (1.4RC) plus as long as pin 2 stays low: A caveat: most jellybean PNP transistors have an emitter-base breakdown voltage of around 7V, and are rated at around 5V absolute max, so if you run the timer with a Vcc of = 5V it would be prudent to put a diode in series with the emitter: +V | +-------+ | |8 [Rt] +---+---+ | 2|_ Vcc |3 IN---+-------------------|--O|T OUT|-- OUT | | 6| | | +---|TH | [1000] | 7|_ 7555| | +--[1n4148]---+--O|D | | | +| | GND | | E [Ct] +---+---+ +--B PNP | |1 C | | | | | +--------------+-------+ | GND -- John Fields Professional Circuit Designer |
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