Electronic ON-OFF (toggle) Switch Quesiton

[ViReN]

Hello Great Guys.....

Again, I have fallen in to trap /ubbthreads/images/graemlins/smile.gif this time... its the switch....

Consider a situation of 2 * CR2032 Cells Driving (rather Overdriving) 2 White LED's. A Tact switch can offer momentary on/off function. but, is there any circuit that can be used so that same Thru Hole Tact switch be used as a ON/OFF Toggle Switch (like the Photon Freedom's switch) .....Nah.. i dont want multiple functions as the photon's .... just one simple plane ON/OFF Toggle function. .....

Transistor's FET's etc (including SMD's are now OK for me /ubbthreads/images/graemlins/smile.gif )

Low component count requested, easily available components, low "off" current drain would be ideal situation.

Any Suggestions / Guidance / links ... etc...

Thanks in Advance,
ViReN

 

[Doug Owen]

Re: Electronic OF-OFF (toggle) Switch Quesiton

If I'm following what you want, sure. Any of a number of CMOS flip flops should work fine. Clock them with your NO push button switch, drive a FET with the output.

It might take a bit of fiddling with resistors and capacitors to debounce the switch.

I'd hit the 40XX specs looking for low current and try a 2N7000 for the FET. FWIW I'd also include at least a resistor to control the currents.

Doug Owen

 

[ViReN]

Hello Doug,

Thanks for the response. The concept of using a Normally Off Push button switch to give a pulse to the CMOS Flipflop through a resistor controlled current which in turn will switch on the FET is excellent. but since i am a totally novice & newbie, can you please tell me any kind of schematics & partnumbers ? and i hope that it will take just one NO Push Button .....

I did try to search.. but got very very complex circuits. But from what you have suggested, it should majorly use only 3-4 components.
1) the NO Switch,
2) CMOS Flipflop
3) FET
4) Resistor.

I think, this is all that is needed, isnt it ?

Please guide me.

Thanks & Regards,
ViReN

 

[ViReN]

Hi Again,

I did manage to get many many circuits, Here is one that I would like to quote, Its very simple, true, but I have a few quesitons regarding it. Can any one help me out ?

almost half of the pins of this chip are unused, Is there any other chip that can perform same function, I have very very limited space .. may be 1 sq cm on board to implement this kind of solution....

Also, from basic knowledge, i can understand that i can use my "Load" instead of the relay, but Can such kind of circuit work with the low voltage ? and can it perform well .... in "Off" condition ? i mean... there should be very very less battery drain during this state.

is there any other small may be transistor based Bi-Stable Flip-Flop circuit ?

Thanks & Regards,
ViReN

 

[Doug Owen]

You're on the right track. This is a dual FF, you're right, half is doing nothing. You can use a lot of similar CMOS parts. The standby current is only a few micro Amps. These parts run OK at 3 Volts typically. Use a FET, not a bipolar. There are lots of packages available.

Yes, RTL circuits to do this exist, but if real estate is at a premium, surface mount CMOS is probably a better call.

Doug Owen

 

[markus_i]

Yes, looks about right. Problem is your low supply voltage - I'm not sure whether the 4027 will work a 3 volts, but there are 74something (LS? HC?) circuits that will. In any case, you'll usually get two FFs in one package - just tie the likely input pins to either Vcc or ground.

The major problem will be the FET - there aren't that many around that work really good at 3 volts, so look for a 'logic level' FET with a low Rds_on (a normal FET might give you a better Rds_on on the paper, but if you check closely, this will mean driving the gate at around 9..12 Volts).

Size on the other hand is not a problem - 1 cm² is lots, but you will have problems in soldering the parts.

Bye
Markus

 

[MrAl]

Hi Viren & others,

Here's one here:

The switches here are those really low cost low current
momentary push 'on' ones.
Note this is shown powering a luxeon star 1 watt (not
three watt) but it could work for that too. The lowest
voltage is probably about 2 volts.
Very low 'off' current draw.
Change input voltage as required.
Because this is shown powering an LED in series with
a resistor, the series resistor is required...but this
resistor of course isnt required for other applications
that say power a switcher.
If you change the FET type it must be a low gate
voltage type if you intend to use it at very low
voltages such as 2 volts.
In you intend to use it with high voltages such
as 10v and over you probably need a zener from
the MOSFET gate to ground to limit the max
gate voltage to the MOSFET. The zener should be
a 9v type or less as required to meet the spec.

Someone asked this same question around March 2004
and i posted that schematic then someone else posted
one with a toggle effect switch action. It's here
in the CPF forum somewhere--just do a search.

Take care,
Al

 

[djpark]

[ QUOTE ]
MrAl said:Someone asked this same question around March 2004 and i posted that schematic then someone else posted one with a toggle effect switch action. It's here in the CPF forum somewhere--just do a search.

[/ QUOTE ]

The post MrAl refers to is here.

http://www.candlepowerforums.com/ubbthreads/showflat.php?Number=524068

Also the single button version mentioned in the same post is found here.

http://www.qsl.net/yo5ofh/hobby%20circuits/miscellaneous.htm

Go down untill you reach "High Current MOSFET Toggle Switch with Debounced Push Button." section.

-- dj

 

[ViReN]

Hey... Thanks every one for kool responces....

I have a couple of questions again....

Doug: Is there any thing like 20XX (single FF) (i am searching) but didnt get any useful results as yet.... .... I will use a FET instead of a bipolar transistor..... As markus_i has said... the circuit wont work for 3 volts ???

Markus_i: You saying that the circuit probably wont work at 3 volts.... and also the FET's .... Any links... hints.. where i can look around... my google friend is giving me a googly at times... showing me same pages in different headings !!....

Mr_Al: You offer a great circuit.... i have a few questions for that circuit.. .... i am guessing that the resistance R1 is there for current limiting purposes...but if the circuit is powered by a CR2032 battery (coin cell) I think, it wont be needed ? am i correct? .... can you please tell me what would be the 'off' current drawn ? (i am very concerned) because i would be using a CR2032 cell... whoose capacity itself is about 200 mAh /ubbthreads/images/graemlins/wink.gif .... Can we modify this circuit to use a single pushbutton switch?

djpark: Thanks for the links, i have viewed the circuits... There are a couple of circuits but /ubbthreads/images/graemlins/frown.gif all of em have stated to work at 6 - 12 volts....

Thanks & Regards,
ViReN

 

[markus_i]

Hi ViReN,

regarding 3V logic - I'm out of that part of business for some time now. I'd suggest you go to one of the logic circuits manufacturer's website and check for low voltage logic circuits. 3 (or 3.3) V should be quite common. It's just that the older series (like the 4000) were designed when 5V+-5% was the standard.
For example:
- go to www.texasinstruments.com, type 'low voltage logic' into the keyword search
- result list will show you a lot of obsolete parts, but you'll see that low voltage has the suffix LVC
- from there, finding the Flip-Flop parametric tables in the 'TI home > Digital Logic' section shouldn't be too difficult
- in this table, you'll see (for example) that low voltage means 0.8...2.7V, but that there are also other families with other/broader voltage ranges.

The only remaining problem after that is actually finding somebody who will sell you the part. You might try ordering a few as samples (usually for free) directly from the manufacturer. If you do this, please be honest when you fill in the questionnaire - a lot of manufacturers are willing to ship out a few samples also to hobbyists, but if too many hobbyists try to convince the manufacturers taht they're big business, it will ruin the sample shipping for everybody in the long run.

HTH,
Bye
Markus

P.S. The same goes for the transistor - and you'll have to know what you want before you can go and search for it.

 

[MrAl]

Hi again,

Viren:
The 'off' current is something like 50ua so it's not
high at all, and very insignificant.
Also, djpark found the circuit i was talking about.
You have to scroll down the page to find the single
switch circuit with the MOSFET.
As soon as i get a chance i'll look into modification
for my circuit to use a single pb switch instead of two,
but it does complicate the circuit to do that.

djpark:
Thanks for finding that circuit again.

Take care,
Al

 

[Doug Owen]

Friends,

You're working too hard. As I said above, he's on the right track, the 4027 he's suggesting works fine at 3 Volts, and is under *4 uA* in standby at room temperature. Jameco will sell them in DIP for $.32 or SMD (SOIC) for the size queens at $.39. Prices drop at 10 each. Time to buy a few parts a make a prototype or two.....

Doug Owen

 

[Doug S]

[ QUOTE ]
Doug Owen said:
Friends,
You're working too hard
Doug Owen

[/ QUOTE ]

True. And too big too. From the first post the application seems to be a 2Xcoin cell configuration. Single gate flip-flops are available in SOT23, SC70, and even smaller BGAs that operate down to Vin<2V. Fairchild, TI, and STM among others make them. Check your Digikey or Mouser catalog. For this particular application a very low Rds Mosfet is not required so some in the size of SC70 would do. Along with the necessary RC for switch debounce and the main current limiting resistor, the whole circuit should fit on 1cm^2 without even trying hard. Standby [OFF] current drain of about 1uA.

 

[ViReN]

Ok.... So Its a Greeeat News for me now /ubbthreads/images/graemlins/smile.gif

I will be making a schematic.. using the 4027 & FET .... will update it here soon....

current drain of 1 uA & 4 uA are good enough.. even 50 uA is good too.... because it is in Micro Ampers /ubbthreads/images/graemlins/smile.gif

Great things /ubbthreads/images/graemlins/smile.gif

Thanks & Regards,
ViReN