On Thursday, February 2, 2023 at 10:45:05 AM UTC-6, Ricky wrote:
> On Thursday, February 2, 2023 at 3:40:23 AM UTC-5, rhor... wrote:
> > On Thursday, February 2, 2023 at 2:21:13 AM UTC-6, Ricky wrote:
> > > On Thursday, February 2, 2023 at 2:58:47 AM UTC-5, rhor... wrote:
> > > > On Tuesday, January 31, 2023 at 1:35:31 PM UTC-6, Ricky wrote:
> > > > > On Tuesday, January 31, 2023 at 6:46:30 AM UTC-4, John Walliker wrote:
> > > > > > On Tuesday, 31 January 2023 at 08:56:30 UTC, rhor... wrote:
> > > > > > > On Monday, January 30, 2023 at 10:59:57 PM UTC-6, Ricky wrote:
> > > > > > > > On Tuesday, January 31, 2023 at 12:43:59 AM UTC-4, rhor... wrote:
> > > > > > > > > On Monday, January 30, 2023 at 3:43:30 AM UTC-6, bill.... wrote:
> > > > > > > > > > On Monday, January 30, 2023 at 8:16:01 PM UTC+11, rhor.. wrote:
> > > > > > > > > > > I have a situation where I need to change a momentary switch to an on / off switch. This is ordinarily very easy using a JK Flip Flop, but there is a twist. The device runs on a 6S Lithium battery, so the voltage will vary from about 18V to 25V or so. In addition, I need the power control circuit to use very little current - on the order of 100 uA - when off. It can use much more power when on - 20 mA or so is no problem.
> > > > > > > > > > You should be able to build a J/K flip-flop with discrete transistors - there are N-channel and P-channel MOSFETs that can take that kind of voltage.
> > > > > > > > > >
> > > > > > > > > > The gate-oxide isn't that robust, so you might need level shifters to make the logic work. It won't have to be that fast, so the level shifters won't need a lot of current.
> > > > > > > > > >
> > > > > > > > > > Classic CMOS is good for logic rails up to about 18V, but if there a 25V version I haven't heard of it.
> > > > > > > > > >
> > > > > > > > > > --
> > > > > > > > > > Bill Sloman, Sydney
> > > > > > > > > Yeah, that is my notion. I need some details.
> > > > > > > > What is your notion? 4000 series CMOS won't handle the battery voltages you are talking about. You would need to add two transistors and a voltage regulator to make a 4000 series part compatible with high side switching your 25V power rail. You can do the same job with just the two transistors, no regulator and no 4000 series CMOS. I provided links to some sample circuits.
> > > > > > > >
> > > > > > > > Maybe you could provide a bit more feedback of what you see here that you like and don't like, and why? Feedback would help a lot.
> > > > > > > >
> > > > > > > > --
> > > > > > > >
> > > > > > > > Rick C.
> > > > > > > >
> > > > > > > > + Get 1,000 miles of free Supercharging
> > > > > > > > + Tesla referral code - https://ts.la/richard11209
> > > > > > > No, your idea (figure 3) is perfect. Adding in control from the (existing) Arduino gives me:
> > > > > > >
> > > > > > > http://siliconventures.net/images/Flashlight%20Switch.PNG
> > > > > > >
> > > > > > > I don't know if there is a better solution than the opto-coupler, but it is definitely a quick and easy solution to interface with the Arduino.
> > > > > > Won't the phototransistor get unhappy with reverse bias? A better optocoupler would
> > > > > > use a symmetric photofet. Something like the H11F1 would work, but there are others.
> > > > > If isolation is not required, and a common ground is used, there are analog switches which should handle 25V. But I would not say an opto is overkill. At least a transistor short won't fry the Arduino.
> > > > >
> > > > > --
> > > > >
> > > > > Rick C.
> > > > >
> > > > > -+ Get 1,000 miles of free Supercharging
> > > > > -+ Tesla referral code - https://ts.la/richard11209
> > > > Yeah, exactly. "Not that the Arduino is exactly expensive, but the relay is cheap insurance. The ground is common, but the supply rail is not, of course. The opto-coupler also insures no part of the circuit draws any current when the switch is off. According to circuit analysis, the current leakage should be under 2uA. That way exceeds the design parms. I love it!
> > > So your intent is that the Arduino only turns the circuit off? I don't think the opto as drawn can turn it on.
> > >
> > > --
> > >
> > > Rick C.
> > >
> > > --- Get 1,000 miles of free Supercharging
> > > --- Tesla referral code - https://ts.la/richard11209
> > Correct. No matter how the circuit gets drawn, the Arduino will be dead when power is off, so it can't turn on the device in any case. It doesn't matter, however. The only control I want the Arduino to have is the ability to shut down to protect the battery from over-discharge. The person holding the unit will turn it on and off, except when the battery is low.
> You never said the Arduino is powered by this power source. If so, the Arduino doesn't need isolation. A simple transistor can ground the gate of X2, turning it, and the entire power unit off. Optoisolators are more expensive than transistors, buy a good margin... not to mention smaller.
>
> --
>
> Rick C.
>
> --+ Get 1,000 miles of free Supercharging
> --+ Tesla referral code - https://ts.la/richard11209
Well, the issue is the potential on both sides of switch 1 is much higher than the Arduino can handle if exposed directly, and even with the base or drain isolated by a resistor, a transistor is either always going to be on or else can never be turned on. Two complementary transistors could do it, but the opto-isolator is a bit more elegant. An H11F1M should do nicely, and I just happen to have a ton of them on hand.