eev blog 262

[jsoderquist]

I'm still trying to wrap my head around your comment concerning tapping the white board, Dave - people really complained about it? That baffles me.

[EEVblog]

I'm still trying to wrap my head around your comment concerning tapping the white board, Dave - people really complained about it? That baffles me.

Yep, they do.
For every nit-picking thing in my videos, you can be sure their will be someone who complains about it!

Dave.

[Rerouter]

your way to good at laughing at nitpickers

[stryker]

Hi Dave

Thanks for the inspirational videos (and fwiw no problems here with the whiteboard tapping either!).

Apologies for the newbie question.  Have just started with electronics and want to take this to a breadboard for a play but don't have a P channel MOSFET in the supplies just yet.  At one stage your diagram had IRF9110 marked on there.  Is there anything special in the selection, or will any P-channel do for the sake of the exercise?  From google-fu it looks like IRFD9110 is the breadboard-friendly one?

Thanks
Geoff

[Greg323i]

Personally, I found it annoying, but you know what? Why complain about some little pittily bullshit thing when I'm gaining so much great information. If it annoyed me that much I wouldn't watch the videos and I'd STFU!!! It's rather cliche, but if you don't have something nice to say, then STFU!!

Just my little ol' opinion! 

[Rufus]

A patent applied for variation

http://www.faqs.org/patents/imgfull/20090237065_01

I recently had the same requirement except one side of the push button is ground. I don't think there is a  two transistor plus a few passives solution to that one.

To control a battery supply you should also have an automatic low battery turn off to prevent complete battery discharge. For the uSupply the processor monitors the battery so it would probably be better to use a processor pin which could do the automatic turn off and on/off latching.

[Neilm]

I'm still trying to wrap my head around your comment concerning tapping the white board, Dave - people really complained about it? That baffles me.

Yep, they do.
For every nit-picking thing in my videos, you can be sure their will be someone who complains about it!

Dave.

You should have had the evil laugh going when you were tapping it    MWhahahahahahahaha

Neil

[IanB]

I'm still trying to wrap my head around your comment concerning tapping the white board, Dave - people really complained about it? That baffles me.

Yep, they do.
For every nit-picking thing in my videos, you can be sure their will be someone who complains about it!

Dave.

Hmm. If you really want to send a message you could try a big sheet of paper and a felt tip/marker pen (see numberphile). All sorts of nice squeaky, scratchy noises available there to entertain people 

(And yes, half the YouTube comments are from people complaining about the squeaky pen noises. You are not alone with nitpickers...)

[Chet T16]

Whiteboard tapping highlights my audio sync issues

[king.oslo]

Hi Dave

Thanks for the inspirational videos (and fwiw no problems here with the whiteboard tapping either!).

Apologies for the newbie question.  Have just started with electronics and want to take this to a breadboard for a play but don't have a P channel MOSFET in the supplies just yet.  At one stage your diagram had IRF9110 marked on there.  Is there anything special in the selection, or will any P-channel do for the sake of the exercise?  From google-fu it looks like IRFD9110 is the breadboard-friendly one?

Thanks
Geoff

Geoff,

Use any. You got to check the datasheet and find its V_GS. It has to be more negative than your GND to rail voltage. It also have to be rated high enough for the main voltages and currents which it will conduct.

Kind regards,
Marius

[electroguy]

Dave, can you please use a blackboard and some chalk in your next few videos. i can't believe people actually complain about stuff like this. lol

[Zad]

I've got you all beat.  $0.33 each.

[Pushbutton switch]

 

That's my solution too. Cheap, reliable, small. Or use a rocker. Something like this is less prone to casual knocks. There is something reassuring about a click as contacts make or break. That feedback is part of what generates perceived product quality. Soft switches are a bit... vague.

[johnnyfp]

But wheres the fun in that? Rocker switches are mmh, old school. Momentary push switches are hip and trendy 

But in either case, I can't get this new and revised version working in my spice emulator.  The old one with two transistors works, but this new one with either one transistor or two Mosfets, I just can't get to emulate. I'm wonder how sensitive the balance of the values or fet/transistors I used can affect the simulator.



Jfp

[kaz911]

I would say - use an XOR gate driving the mosfet - and tie the output of the mosfet to on input pin - and other XOR to the switch with a cap.

Switch 0v - VccIn 0v - output 0v (stay off)
Switch 5v - VccIn 0v - output 5v (switch on)
Switch 0v - VccIn 5v - output 5v (stay on)
Switch 5v - VccIn 5v - output 0v (switch off)

Seems a bit simpler in component count. But I don't know about cost..

/kaz

[Bored@Work]

I'm wonder how sensitive the balance of the values or fet/transistors I used can affect the simulator.

It is rather sensitive. And just putting 100k resistors everywhere won't cut it. You need to dimension each resistor and the cap appropriately. For example, R5 is likely too large to drive Q2 as switch. But on the other hand, it shouldn't be to low, otherwise it gets difficult to turn the transistor off. And add a capacitive load, since the load has influence on the behaviour, making the circuit even more sensitive.

In general, I don't see much advantage compared to a mechanical switch, especially because the soft switch is not controlled by the micro. If it would be controlled by the micro one could add some features like auto-turn-off when idle (no current drawn for x minutes -> turn off), which might be interesting for a battery powered device.

[SeanB]

Only issue I have is humid environments. Leakage can do odd things then.

[FreeThinker]

Toggi, I did look at your solution, but I couldn't get it to work fully when you start adding capacitance to the load.

Dave reckons his answer of how to use seven parts including the switch was in front of his eyes, but I still cannot see it.

Toggi had it essentially right, except it uses a MOSFET instead of the BJT, thus needing one less resistor.
But as it turns out, it seems it's not new, somebody tweeted the same thing on a Russian site:
http://www.uschema.com/safe_power_switch/

It became really obvious on second thought, because I was obsessed with doing the turn on/off using the gate connected BJT. But when you think about the using the gate of the P MOSTFET itself, it's obvious the existing RC can be used and there is no need for the 2nd latch BJT

Dave.

Truly there is nothing new, nice try anyway Lol.

[siliconmix]

amspire : now that i think about it and after i tested a little, you are right. If the load is capacitive and has a large capacitance then the functionality is quite weird.
If you match the capacitance of the load in the timing capacitor then you can kinda make it work but the timings are quite large.
I really have to start thinking laterally when trying to understand circuits

Later edit: This is what i mean http://goo.gl/RCZUI

hey i like that falstad applet.why havent i seen this before ?

[PA3BNX]

Hello Every body,

I didn't see no comments on the fact that there could be RF present on the input and output
of this switch hi...

But I maybe should add a diode in series with the capacitor so the voltage will drop
to zero also if there is almost or no load.

There are many TFT TVs that switches on and off if I transmit close to it with my 2/0.70m  5 Watt  handheld.

Very annoying hi...

[bpkdasbaum]

Hi everyone,

I went on a crusade for several hours to find me a latching momentary switch, until I finally ended up here. Though I should have checked this blog first >_> since i've been watching the videos now and then, informative and fun! Thx by the way Dave.

Now, I really don't understand most of technical background stuff here and would like to get some help with the parts.

I would like to know if the schematic will work this these transistors, since I can't find the exact ones used in the video/schematics, but according to the data sheets i've looked up, they are pretty much the same.

I am using this schematic as a reference, since Dave said in a post here, that is pretty much the best solution and is the same he came up with too after making his video:




Infineon BSS 123 N datasheet
IRLML6401 datasheet


So can i use those 2?

Thanks in advance

[amspire]

That circuit was the best in terms of least components, but it does not work well if your load has capacitors across the supply rails. The one I did back on the first page of posts has one extra resistor, but it is the one that works best with a capacitive load.  The circuit is from LTSpice, so there is extra junk in the diagram for the simulation.

To me the method in general is not a robust solution as it depends a so much on the way the load behaves. For example, a transient from the load circuit can turn the supply on, even if the switch is not touched. If your load was a linear regulator IC with a reverse diode across it, and you attach an external load to the regulator output which happens to have a charged supply cap, then this switch circuit will turn itself on

Richard.

[bpkdasbaum]

i don't have anything fancy in the main circuit, just a 9v battery and 3 fans, thats it. But space is an issue, thus I am aiming for the one with the least parts, it should work just fine.
I just need to know, if it will work at all with those 2 transistors.

[T4P]

i don't have anything fancy in the main circuit, just a 9v battery and 3 fans, thats it. But space is an issue, thus I am aiming for the one with the least parts, it should work just fine.
I just need to know, if it will work at all with those 2 transistors.

Be careful of inductive spiking .

[amspire]

i don't have anything fancy in the main circuit, just a 9v battery and 3 fans, thats it. But space is an issue, thus I am aiming for the one with the least parts, it should work just fine.
I just need to know, if it will work at all with those 2 transistors.

You will have to check to see if the fans generate any voltage while they are slowing down. If they do, they will turn the switch back on just after you press the button to turn the switch off.

Richard.

[billclay]

I'm still trying to wrap my head around your comment concerning tapping the white board, Dave - people really complained about it? That baffles me.

Yep, they do.
For every nit-picking thing in my videos, you can be sure their will be someone who complains about it!

Dave.

Dave, you are using the wrong color marker on the whiteboard.  Please stop it.