dc power on-off with single pole momentary switch

[John Bachman]

The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

 

[Jim Thompson]

The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

Input Voltage?

How much "stand-by" power can be drawn by the switching circuitry?

Load Current?

...Jim Thompson

 

[Jan Panteltje]

The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

Use a 74HC74 flipflop, it has reset for correct power up too.
Screw the comparator.

 

[John Bachman]

Input Voltage?

How much "stand-by" power can be drawn by the switching circuitry?

Load Current?

9 volt battery supply. Load is 12 ma. I figure a pass transistor
operated by the switch and/or circuitry will be fine.

Ideally the switching circuitry is on the load side of the pass
transistor, hence no quiescent draw. That may not be possible. If it
must draw quiescent current then I will have to assess the feasibility
of it. Two switches is not the end of the world, just not as elegant.

John

 

[John Bachman]

Use a 74HC74 flipflop, it has reset for correct power up too.
Screw the comparator.

Yeah, I know. Sigh.

John

 

[Adrian Tuddenham]

9 volt battery supply. Load is 12 ma. I figure a pass transistor
operated by the switch and/or circuitry will be fine.

Ideally the switching circuitry is on the load side of the pass
transistor, hence no quiescent draw. That may not be possible. If it
must draw quiescent current then I will have to assess the feasibility
of it. Two switches is not the end of the world, just not as elegant.

Is there any reason why you can't use a straightforward single pole
toggle switch? It is cheap, ergonomic to operate, draws no quiescent
current when open, gives negligible volt-drop when closed - and is
self-indicating.

If they had only just been invented, they would be regarded as one of
the biggest steps forward in technology of the past 30 years.

 

[linnix]

The subject tells the goal. Here is the rest of the story. There is
Why not? Bad design!

It is preferred to use a dual comparator such as

Is there any reason why you can't use a straightforward single pole
toggle switch?

Yes, it can't turn itself off.

It is cheap, ergonomic to operate, draws no quiescent
current when open, gives negligible volt-drop when closed - and is
self-indicating.

If they had only just been invented, they would be regarded as one of
the biggest steps forward in technology of the past 30 years.

Except for wasting batteries. Auto off is the second biggest step
forward ...

 

[Paul Hovnanian P.E.]

The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

Go down to your local hardware store. They have lamp switches that push
on, push off. All done mechanically.

 

[Adrian Tuddenham]

Yes, it can't turn itself off.


Except for wasting batteries. Auto off is the second biggest step
forward ...

Unless the item is a camera which switches itself off just in time to
miss as the shot you have been waiting for !

 

[linnix]

Go down to your local hardware store. They have lamp switches that push
on, push off. All done mechanically.

But many customers just push on and leave on battery devices. On
second thought, I am going to randomly disable the auto-off feature.
I am starting a batteries on-line business.

 

[linnix]

Unless the item is a camera which switches itself off just in time to
miss as the shot you have been waiting for !

But the camera button (trigger) should be auto-on as well.

 

[Tam]

Go down to your local hardware store. They have lamp switches that push
on, push off. All done mechanically.

And if you need to switch more current than the lamp switch can handle, use
it to operate a power relay. BTW, if you go the 7474 route, be sure to
debounce the switch.

Tam

 

[Arie]

The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

Something like this?


+
| ====
100k GND- 10n -------o o------ 1uF -- GND +
| | | |
| | |\ 1M 10k
|-- 100k ----------|-\ | |
| | }--------------------------------->
|-- 100k ----------|+/ |
| | |/ |
| | |
| ----- 100k ---
100k
|
GND

The comparator is self-latching, after power-on output is high (for minimum
current drawn).
Alternative: connect the 10n to +, then it starts with output low.

Pressing the switch less than 1 sec switches the state.
Repeating the switch presses fast does not switch state (slow debounce).

Arie de Muynck

 

[John Bachman]

Is there any reason why you can't use a straightforward single pole
toggle switch? It is cheap, ergonomic to operate, draws no quiescent
current when open, gives negligible volt-drop when closed - and is
self-indicating.

If they had only just been invented, they would be regarded as one of
the biggest steps forward in technology of the past 30 years.

Cost is the only objection. A tactile momentary costs .16. A toggle
is a buck or more. When the total product part cost is $12 then $.84+
is lot.

Two momentaries cost $.32 and will do the job, but Oh, that is ugly.

John

 

[Adrian Tuddenham]

Cost is the only objection. A tactile momentary costs .16. A toggle
is a buck or more. When the total product part cost is $12 then $.84+
is lot.

Two momentaries cost $.32 and will do the job, but Oh, that is ugly.

I'd be willing to pay the extra for a decent switch, but I suppose it
depends on which sector of the market the product is aimed at.

 

[Jan Panteltje]

Something like this?


+
| ====
100k GND- 10n -------o o------ 1uF -- GND +
| | | |
| | |\ 1M 10k
|-- 100k ----------|-\ | |
| | }--------------------------------->
|-- 100k ----------|+/ |
| | |/ |
| | |
| ----- 100k ---
100k
|
GND

The comparator is self-latching, after power-on output is high (for minimum
current drawn).
Alternative: connect the 10n to +, then it starts with output low.

Pressing the switch less than 1 sec switches the state.
Repeating the switch presses fast does not switch state (slow debounce).

Arie de Muynck

I must say I am impressed, a nice solution.
As to the issue what is 'nest', this uses 10 components, 2 of which are capacitors.

Placing, board size, vias....

I did say 74HC74, but even that requires some debounce, as others have pointed out,
so at least 2 more components.

The OP says he has no micro.
But how a about a simple 8 pin PIC?
Use the internal osc, internal pullup at an input pin, trigger interrupt,
flip output, hang some milliseconds in interrupt routine as debounce.....

It is all there, with *1* component, say a PIC 12F629, only 67 cent in volume.
http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1001&mid=10&lang=en&pageId=74

And, it also has a build in comparator that perhaps can replace some part
of the rest of the circuit.....


I would definitely go that way, have been using that PIC to replace simple circuits
no several times.
That way you need to have only 1 part in store.

 

[Tam]

I must say I am impressed, a nice solution.
As to the issue what is 'nest', this uses 10 components, 2 of which are
capacitors.

Placing, board size, vias....

I did say 74HC74, but even that requires some debounce, as others have
pointed out,
so at least 2 more components.

Actually, that is not that bad, because you use the other half of the HC74
package to debounce. However, to do it right you need a SPDT switch: no
capacitors needed.

Tam