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Mains hum 555 timer circuit problems

M

Midge

Jan 1, 1970
0
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

TIA.

Midge.
 
G

GPG

Jan 1, 1970
0
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

TIA.

Midge.

Replace the 1Nxxx diodes with 1N4148. Use a CMOS 555
 
C

cozz in or out

Jan 1, 1970
0
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

TIA.

Midge.

hi,
dont worry ... i have designed a circuit on 555 timer send mail
kaushik899 @ gmail .com
i will send .

kaushik
 
J

John Fields

Jan 1, 1970
0
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

---
Try this: (View in Courier)


+9V>-------------+------+-------+---------+------+
| |K | |8 |
| [1N4148] [820K] +---+---+ |
| | | 2|_ Vcc _|3 |
IN>---[0.1µF]--[1M]<----+-------|----O|T R|--|--> OUT TO RELAY
| |K | 6| | |
| [1N4148] +-----|TH | |
| | | 7|_ _|4 |
| | +----O|D R|O-+
| | | | GND |
| | |+ +---+---+
| | [1µF] |1
| | | |
| | | |
GND>-------------+------+-------+---------+


With nothing on IN, rotate the 1 megohm pot until OUT goes high,
then back the pot off until OUT goes low.

Now touch IN, and OUT should go high for as long as you keep
touching IN.

If the sensitivity is too high, back off R1 until you get the
sensitivity you need.

BTW, how reliable does the circuit have to be?
 
D

default

Jan 1, 1970
0
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

TIA.

Midge.

I have a circuit just like that. Mine is a "lightening detector"
(spark) detector. It has a pot to set the sensitivity and a single
common npn transistor to amplify the signal into pin 2. (pulse is
capacitively coupled into pin two like it shows in the application
notes - 10 K pullup on 2 with a .1 ufd cap to take the negative
transition into it).

2N2222A has a 10K pull up on its collector and the base goes to a wire
that detects the static with a crude high pass filter, since I don't
really want it triggering on hum. If I touch the antenna it triggers
very reliably, so I'm thinking if you add an npn transistor to amplify
the touch plate and use AC coupling for the trigger you should have
what you want.

My device also triggers with one of those piezo electric igniter used
for lighting propane grills from about four feet away. Antenna is a
1' piece of wire.
 
B

Brendan Gillatt

Jan 1, 1970
0
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
I found a circuit in an old book of 555 timer projects for a non-latching
mains hum single plate touch switch, but I just can't get it to work!

The touch plate is connected to pin 2 of the 555 via a 0.1uF capacitor.

Pin 2 is also connected to the cathode of an IN4001 diode, and the anode of
that diode is connected to 0v

Pin 2 is also connected to the anode of a second IN4001 diode, and cathode
of that diode connects to Vcc. A resistor which supposedly sets the
sensitivity of the circuit is connected in parallel with this diode between
pin 2 of the 555 and Vcc - suggested values "in the range 47K-10M"

According to the book, the 555 should trigger permanently when the resistor
value gets as high as 10M. It doesn't, nor at 20M, nor 30M. This suggest to
me there is a flaw in the design.

I can get it to work with some stability (but not enough!) by simply
connecting pin 2 to the touch plate via a longish wire. I suspect this is
because the wire is picking up background noise sufficient to stop the 555
triggering, and my finger is then dragging the signal down a bit, and the
555 then triggers.

I can also get it to work by going for a leakage based (i.e. two contact
pad) solution of connecting pin 2 to Vcc via a 10M resistor and one pad to
pin 2 and a second to 0v - but it's not that sensitive + I really could do
with a one-pad solution.

Other info about the circuit:

Supply is a 9v battery. There is no indication the circuit needs to be
grounded.
Pin 6/7 are connected to 0V via a 1uF capacitor, and to Vcc via an 820K.
Pin 5 connects to 0v via a 01.uF capacitor.
I'm operating it in the house where there should be plenty of mains hum to
drive the circuit
Pin 3 drives a 9V relay via another IN2001 diode (another IN4001 diode + 1uF
capacitor sit across the coil of the relay)

So if anyone has:

1. Any ideas for getting this circuit to work properly and reliably
OR
2. A really good proven one pad non-latching circuit design which can
preferably run from battery and doesn't need to be grounded
OR
3. Any other proven one-pad non-latching design. I won't rule out a solution
that needs to be grounded and/or mains powered., but its just not as
convenient.

TIA.

Midge.

FWIW, you can buy a really, really cheap chip
(http://www.qprox.com/products/qt100.php) for less than the cost in
parts for your circuit (yeah I know it's not as fun though). They just
require a resistor & capacitor to work. I've used these chips a number
of times and they work perfectly. There's no calibration involved and
they draw next to nothing from Vcc.

- --
Brendan Gillatt
brendan {at} brendangillatt {dot} co {dot} uk
http://www.brendangillatt.co.uk
PGP Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xBACD7433
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M

Midge

Jan 1, 1970
0
Just a bit of background.....

I'm setting up the switches to help someone who is nearly paralysed with MS
to control a few things around her - hense the need for a one pad solution
for ease of use.

Switching does need to be pretty reliable so I'll try some of your ideas and
see how I get on.

Thanks for the prompt help.

Midge.
 
C

cozz in or out

Jan 1, 1970
0
Just a bit of background.....

I'm setting up the switches to help someone who is nearly paralysed with MS
to control a few things around her - hense the need for a one pad solution
for ease of use.

Switching does need to be pretty reliable so I'll try some of your ideas and
see how I get on.

Thanks for the prompt help.

Midge.

in message







- Show quoted text -

hey midge ..did my circuit helped you .... ???
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
pin 2 requires 50 micro to trigger so now we need a pulse to go negative tie a pullup to the rail from pin 2
add a cap in series with pin 2 now if you touch ground with your finger it should discharge the cap making pin 2 spike on down. that should trigger it however once triggered it will stay latched until time out
 
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