Help with 555 circuit please...

[Jeannot]

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

 

[Jeannot]

I'd like to add that my assumption of having to run the 555 at 12V is
wrong.

Also, any idea about using something else than a 555 is welcome, I was
hoping to keep the (active) parts count to around 1.

 

[Jamie]

Jeannot wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

You only need a small NPN transistor..

a 2N2222 type will work fine.

Emitter to common, Base input will have like a 1k ohm R which is
connected to the 12 volts of the AV receiver.. The collector will
connect to the PS wire of the PC.

P.S.
Don't allow the input of this circuit to float..
you may want to place a parallel R on the input, something like
4.7k should be fine.


http://webpages.charter.net/jamie_5"

 

[Jeannot]

On Mar 16, 7:15 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Jeannot wrote:
I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

  You only need a small NPN transistor..

   a 2N2222 type will work fine.

   Emitter to common, Base input will have like a 1k ohm R which is
connected to the 12 volts of the AV receiver.. The collector will
connect to the PS wire of the PC.

   P.S.
     Don't allow the input of this circuit to float..
  you may want to place a parallel R on the input, something like
  4.7k should be fine.

http://webpages.charter.net/jamie_5"

This solution will keep the PC power low, preventing it to power up.
That is why it has to be a pulse.
The solution must generate a pulse on 0-12V, but also on 12-0V.

 

[Jamie]

Jeannot wrote:

On Mar 16, 7:15 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Jeannot wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

You only need a small NPN transistor..

a 2N2222 type will work fine.

Emitter to common, Base input will have like a 1k ohm R which is
connected to the 12 volts of the AV receiver.. The collector will
connect to the PS wire of the PC.

P.S.
Don't allow the input of this circuit to float..
you may want to place a parallel R on the input, something like
4.7k should be fine.

http://webpages.charter.net/jamie_5"


This solution will keep the PC power low, preventing it to power up.
That is why it has to be a pulse.
The solution must generate a pulse on 0-12V, but also on 12-0V.
Ok, didn't think of that, place a capacitor on the input of the

same circuit.. This will generate a transient (+) pulse. Shunt R on
both sides incase you operate the input in high Z at times, this will
keep the cap discharged to insure proper on cycling.

cap.
-----[]-------/\/\/\----- to base of NPN
^ ^
4.7k shunts to common.

You most likely want like a .5 second pulse..

T = RC; T = time in seconds to charge to 63% C is in Farads.

C = .5/R = 106uf.

That is just a rough idea, this circuit isn't really anything
that advance and I do think the PS will handle a sloping release
on the PS switch line.

http://webpages.charter.net/jamie_5"

 

[Jeannot]

On Mar 16, 10:22 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Jeannot wrote:
On Mar 16, 7:15 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Jeannot wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

 You only need a small NPN transistor..

  a 2N2222 type will work fine.

  Emitter to common, Base input will have like a 1k ohm R which is
connected to the 12 volts of the AV receiver.. The collector will
connect to the PS wire of the PC.

  P.S.
    Don't allow the input of this circuit to float..
 you may want to place a parallel R on the input, something like
 4.7k should be fine.

http://webpages.charter.net/jamie_5"

This solution will keep the PC power low, preventing it to power up.
That is why it has to be a pulse.
The solution must generate a pulse on 0-12V, but also on 12-0V.

Ok, didn't think of that, place a capacitor on the input of the
same circuit.. This will generate a transient (+) pulse. Shunt R on
both sides incase you operate the input in high Z at times, this will
  keep the cap discharged to insure proper on cycling.

         cap.
    -----[]-------/\/\/\----- to base of NPN
      ^        ^
        4.7k shunts to common.

    You most likely want like a .5 second pulse..

  T = RC; T = time in seconds to charge to 63% C is in Farads.

  C = .5/R = 106uf.

    That is just a rough idea, this circuit isn't really anything
that advance and I do think the PS will handle a sloping release
on the PS switch line.

http://webpages.charter.net/jamie_5"

Thanks Jamie. Great minds meat, I came up with the same circuit, and
another complementary (PNP) circuit to generate the pulse on 12-0.

The problem I'm having is that this relies on the receiver generating
a clean rising square wave with enough current to charge the caps. I
am not comfortable with that assumption (I do not yet have the
receiver). However, the high-impedance input of a 555 would work.

I have built a monostable 555, that works for the 12-0V. But I found
no monostable circuit that works on the leading edge of a positive
transition. Hmmm, I could invert the input into an identical
monostable circuit, I hadn't thought of that.

I am also considering adding a 741 in follower at the input of the
circuit with the two transistors to provide sufficient current to
charge the caps.

I will make my solution available, I can't believe no one had to do
that before me.

 

[Jasen Betts]

On 2009-03-16, Jeannot <jeannot@hawk.igs.net> wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

555 is the wrong part for this.

+->|-----+--- +5 or +12
| |/
in || | |/-
+---||--[10K]-+-----|
| || |\
| \
| |
| [1K] out
| | /
| | /
| || | |/
+---||---[10K]-+-------+--|
| || | |\|
| | -\
[1K] | \
| | |
+- 0V `---|<---------+- 0V

 

[Jasen Betts]

On 2009-03-17, Jeannot <jeannot@hawk.igs.net> wrote:

On Mar 16, 10:22 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Jeannot wrote:
On Mar 16, 7:15 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Jeannot wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

you could use a CMOS XNOR gate with one input to the pc's main 12V rail and
the other to the 12V input.

this way you'll never get out of synchronisation.

 

[John Fields]

On Mon, 16 Mar 2009 09:13:14 -0700 (PDT), Jeannot <jeannot@hawk.igs.net>
wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

---

From your description, it seems like what you're asking for is this:
(View in Courier)

___________________________________________
AV12V___| |________

12V
____ / ____
PCPSW___| ON |______________________________________|OFF |___

-->| |<--1s 1s-->| |<--


or maybe this:?

___________________________________________
AV12V___| |________

12V
___ ON /_____________________________________ OFF ___
PCPSW |____| |____|

-->| |<--1s 1s-->| |<--

JF

 

[Jeannot]

On Mar 17, 8:14 am, John Fields <jfie...@austininstruments.com> wrote:

On Mon, 16 Mar 2009 09:13:14 -0700 (PDT), Jeannot <jean...@hawk.igs.net
wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

---

From your description, it seems  like what you're asking for is this:
(View in Courier)

         ___________________________________________
AV12V___|                                           |________

               12V
         ____ /                                      ____
PCPSW___| ON |______________________________________|OFF |___

     -->|    |<--1s                            1s-->|    |<--

or maybe this:?

         ___________________________________________
AV12V___|                                           |________

               12V
     ___  ON  /_____________________________________ OFF  ___
PCPSW   |____|                                      |____|

     -->|    |<--1s                            1s-->|    |<--

JF  

Right on John.
You got the timing right, only PCPSW should be open collector,
grounding the PC signal that has an integrated pull-up.
I look forward to your input.

 

[Jeannot]

On Mar 17, 5:42 am, Jasen Betts <ja...@xnet.co.nz> wrote:

On 2009-03-16, Jeannot <jean...@hawk.igs.net> wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

Thanks for your input

  555 is the wrong part for this.

                   +->|-----+--- +5 or +12                                                      
                   |      |/                                                  
   in    ||        |     |/-                                                    
     +---||--[10K]-+-----|                                      
     |   ||              |\
     |                     \    
     |                      |    
     |                    [1K]     out
     |                      |     /                
     |                      |    /
     |   ||                 |  |/
     +---||---[10K]-+-------+--|
     |   ||         |          |\|
     |              |           -\    
    [1K]            |             \
     |              |              |
     +- 0V          `---|<---------+- 0V

Thanks Jasen. I have tried that circuit, but it is too sensitive to
the current capability and rise time of the driving circuit.
One solution would be to have another stage, a king of Schmidt trigger
before.

 

[John Fields]

On Tue, 17 Mar 2009 06:42:13 -0700 (PDT), Jeannot <jeannot@hawk.igs.net>
wrote:

On Mar 17, 8:14 am, John Fields <jfie...@austininstruments.com> wrote:
On Mon, 16 Mar 2009 09:13:14 -0700 (PDT), Jeannot <jean...@hawk.igs.net
wrote:

I have a AV receiver which outputs 12V DC when it's on, and to have PC
power to follow the Receiver power.

If possible, I would like to use the DISCH output of the 555 for the
Power Switch motherboard input. The reason is, it's an open collector,
and would allow me to power the 555 with 12V without damaging the
motherboard.

What I need is:
-When 12V comes, a 1S pulse is generated on the DISCH pin.
-When 12V goes, the same pulse is generated.

---

From your description, it seems  like what you're asking for is this:
(View in Courier)

         ___________________________________________
AV12V___|                                           |________

               12V
         ____ /                                      ____
PCPSW___| ON |______________________________________|OFF |___

     -->|    |<--1s                            1s-->|    |<--

or maybe this:?

         ___________________________________________
AV12V___|                                           |________

               12V
     ___  ON  /_____________________________________ OFF  ___
PCPSW   |____|                                      |____|

     -->|    |<--1s                            1s-->|    |<--

JF  

Right on John.
You got the timing right, only PCPSW should be open collector,
grounding the PC signal that has an integrated pull-up.
I look forward to your input.

---
OK, I'll be happy to help, and I think you can do it with a single 4538,
but there are some issues.

First, is your PC 12V ON all the time?

Second, is the 12V out of the receiver intended to be used as a supply
voltage for accessories or is it just an indicator the RX is ON?
If it's for accessories, how much current can it supply and how well
regulated is it?

Third, what's the difference in the 12V between the PC and the RX?

Fourth, when you turn the RX off does its 12V output go to a hard
ground?

Fifth, what are the rise and fall times of the 12V into, say, a 1000 ohm
load?

JF

 

[Jeannot]

First, is your PC 12V ON all the time?

Yes, and it is 5V. It is the wire that goes to the power switch (which
grounds it momentarly)

Second, is the 12V out of the receiver intended to be used as a supply
voltage for accessories or is it just an indicator the RX is ON?
If it's for accessories, how much current can it supply and how well
regulated is it?  

It is for controlling accessories 12V at 150ma max, well regulated.

Third, what's the difference in the 12V between the PC and the RX?

I have no idea, but again, the PC is 5V. If need be, I have access to
12V on the PC side, normally 12.3-12.6.

Fourth, when you turn the RX off does its 12V output go to a hard
ground?

That's a good question, but my guess would be no. I'd have to test
that but I don't have access to the receiver before next week-end.

Fifth, what are the rise and fall times of the 12V into, say, a 1000 ohm load?

I would have to test that, but a 150ma capacity leads to believe it
can supply a 80 ohms resistor so we can assume it's perform well with
a 1k load.

 

[John Fields]

On Tue, 17 Mar 2009 15:34:45 -0700 (PDT), Jeannot <jeannot@hawk.igs.net>
wrote:

First, is your PC 12V ON all the time?

Yes, and it is 5V. It is the wire that goes to the power switch (which
grounds it momentarly)

Second, is the 12V out of the receiver intended to be used as a supply
voltage for accessories or is it just an indicator the RX is ON?
If it's for accessories, how much current can it supply and how well
regulated is it?  

It is for controlling accessories 12V at 150ma max, well regulated.

Third, what's the difference in the 12V between the PC and the RX?

I have no idea, but again, the PC is 5V. If need be, I have access to
12V on the PC side, normally 12.3-12.6.

Fourth, when you turn the RX off does its 12V output go to a hard
ground?

That's a good question, but my guess would be no. I'd have to test
that but I don't have access to the receiver before next week-end.

Fifth, what are the rise and fall times of the 12V into, say, a 1000 ohm load?

I would have to test that, but a 150ma capacity leads to believe it
can supply a 80 ohms resistor so we can assume it's perform well with
a 1k load.

---
OK, here's a nice, simple, single chip solution for you (View in
courier)


..
.. +5V +5V
.. | |
.. | [R4]
.. +--A |
.. R1 +-----------A Y--+-->SW
..RX+12V>---[750]--+------A | R3 Y-----B U1C
.. | Y--+--[1M]---+-B U1B
.. | +--B U1A |
.. [470] | [470nF]
.. |R2 | |C1
..GND>-------------+---+------------------+------------------->GND


U1A, B, and C are three of the four exclusive-OR gates in a 74HC86, and
R4 is the pullup to 5V that's in the switch circuit already.

You'll need to provide 5V for the '86 and also connect the unused inputs
of the leftover gate to either +5V or GND.

How it works is that when you turn the 12V on and off, U1A will crispen
up its edges and present a nice low impedance to R3 and U1B-A

When U1A-Y goes high, The A input of U1B will go high immediately while
the B input will take some time to go high since it'll take some time
for C1 to charge up to the point where U1B will switch.

Since U1B is an exclusive-OR gate its output will go high when its
inputs are different; otherwise its output will be low.

So, when the 12V is off and C1 is discharged, U1B-Y will be low, when
the 12V is on and C1 is charging its output will be high, and when the
cap charges to the point where U1B will switch, the output will go low
again and stay there.

The same thing occurs when the 12V is turned off, since U1B-A will go
low immediately forcing U1B-Y high until C1 discharges, then U1B-Y will
go low and stay there until the next time the 12V is turned on.

That's just backwards of what we need though, so we wire up U1C as an
inverter and use that output to drive R4, the pullup in your PC.

R1 and R2 are standard 5% 1/4 watt carbon film resistors chosen to drop
the 12V signal to around 4.5V with 10mA of current in the divider, the
actual worst case low voltage out being 4.34V and worst case high 4.91V.

R3 and C1 are chosen for a time constant of about 1/2 second, and R3 is
also a 5% 1/4 watt carbon film. The cap can be pretty much anything,
and ceramic or polyester film would be fine.

JF

 

[John Fields]

On Wed, 18 Mar 2009 09:51:02 -0500, John Fields
<jfields@austininstruments.com> wrote:

---
OK, here's a nice, simple, single chip solution for you (View in
courier)


.
. +5V +5V
. | |
. | [R4]
. +--A |
. R1 +-----------A Y--+-->SW
.RX+12V>---[750]--+------A | R3 Y-----B U1C
. | Y--+--[1M]---+-B U1B
. | +--B U1A |
. [470] | [470nF]
. |R2 | |C1
.GND>-------------+---+------------------+------------------->GND

---
Seems to work...

Version 4
SHEET 1 880 680
WIRE 608 64 576 64
WIRE 736 64 688 64
WIRE -160 96 -224 96
WIRE -32 96 -80 96
WIRE 96 96 -32 96
WIRE 208 112 160 112
WIRE 432 112 208 112
WIRE 640 128 496 128
WIRE 736 144 736 64
WIRE 736 144 704 144
WIRE 96 160 64 160
WIRE 208 176 208 112
WIRE 256 176 208 176
WIRE 384 176 336 176
WIRE 432 176 384 176
WIRE -32 192 -32 96
WIRE 576 192 576 64
WIRE 640 192 576 192
WIRE -224 224 -224 96
WIRE 384 224 384 176
WIRE 576 224 576 192
WIRE -224 336 -224 304
WIRE -32 336 -32 272
WIRE -32 336 -224 336
WIRE 64 336 64 160
WIRE 64 336 -32 336
WIRE 384 336 384 288
WIRE 384 336 64 336
WIRE 576 336 576 304
WIRE 576 336 384 336
WIRE -224 400 -224 336
FLAG -224 400 0
SYMBOL Digital\\xor 144 64 R0
WINDOW 0 -37 125 Left 0
SYMATTR InstName A1
SYMATTR Value2 trise 1e-7 tfall 1e-7 vhigh 5V
SYMBOL Digital\\xor 480 80 R0
WINDOW 0 -41 126 Left 0
SYMATTR InstName A2
SYMATTR Value2 trise 1e-7 tfall 1e-7 vhigh 5V
SYMBOL Digital\\xor 688 96 R0
WINDOW 0 8 109 Left 0
SYMATTR InstName A3
SYMATTR Value2 trise 1e-7 tfall 1e-7 vhigh 5V
SYMBOL res -64 80 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 750
SYMBOL res -16 288 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R2
SYMATTR Value 470
SYMBOL voltage -224 208 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 12 0 .1 .1 5)
SYMBOL res 352 160 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 1e6
SYMBOL cap 368 224 R0
SYMATTR InstName C1
SYMATTR Value 4.7e-7
SYMBOL voltage 576 208 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 5
SYMBOL res 704 48 R90
WINDOW 0 -9 54 VBottom 0
WINDOW 3 39 54 VTop 0
SYMATTR InstName R4
SYMATTR Value 10k
TEXT -200 360 Left 0 !.tran 10

JF

 

[Jeannot]

John, this is exactly what I was after.
Sorry for the late reply, I was out of town all week...

I'll be putting this together in the next few days.

Thanks!