Turn an LED on after it automatically turns off by unaccessable timer.

You might be able to put the resistor in the ground lead. The circuit and the comparitor would be powered after the resistor. Then you could check for a voltage > 400mV and not need a divider. The chip itself is protected from voltages exceeding the supply voltage.

<removed>

Usually, the limits are Gnd-0.3 and V+0.3V. The substrate has an inherent Schotkey diode and when a device is unpowered V+ and GND are both zero. Usually, you have to limit the current for this protection. It would likely defeat the ability to use high value resistors.

These sub things might be scarce, so a good regulated power supply probably makes sense to remove transients and improve lifetime.
 
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I think both designs are do-able:

#1, sense resistor in power gnd lead
comparitor powered after sense resistor.

The comparitor looks back at the battery ground.
It would be equal or 400mV higher than comparitor ground.

If that sensed voltage <400 mV, then the open collector output should be ON.


#2 sense resistor in power lead, regulated 3.3V supply
Comparitor powered after sense resistor.

the comparitor looks at voltage after the sense resistor.
IF <2.9 then the open collector output should be on.
 

Thread Starter

MFL

Joined Aug 13, 2021
41
There is no need to denounce anything on this device. Any contact of the switch and it will activate and the switch doesn't do anything for 20-seconds (even if the user keeps the switch held in). The 555 with an NPN "switch" is the way to go here. Super simple and, most important, the OP understands the solution. It can be made with a simple protoboard - no EasyEDA needed.
I just caught that "denounce" in your text .. and I think you really said "debounce" .. I felt the same way.. I don't need no stinkin' de-bounce here! ... but.. I'm beginning to understand what KISS is doing.. it's a bit sophisticated (for me) and probably worth doing as a good exercise in electrically engineering a problem like this... however, the 555 will work... and this project does not merit sophistication... but then, doing things real cool, is good.
 
I just pointed out "things" to worry about. The 555 does not have these "things" to take into consideration.
My version may take less parts and have a smaller footprint. and no big capacitors. It might give more of a continuous output and it won't be dependent on electrolytic capacitor failure.

The 555 is only good for a few seconds with small capacitors. For fun, someone invented a "programmable" 555 timer. You use a PC. It gets around some of the limitations. http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555C_Spec.pdf

I'll see if i can draw up a couple of schematics,

My first real analog design project was both complex and expensive. It was a biasable 4-terminal current-voltage converter for a lock-in amplifier. It had to have good AC performance which it did. It almost didn't work. I wasn't allowed to complete the DC design and there were two BIG problems:
#1: I had to isolate a capacitive load of our calibration devices.
#2. A few pA across 0V is a lot of offset. A real world issue.
 

MrSalts

Joined Apr 2, 2020
2,767
I just pointed out "things" to worry about. The 555 does not have these "things" to take into consideration.
My version may take less parts and have a smaller footprint. and no big capacitors. It might give more of a continuous output and it won't be dependent on electrolytic capacitor failure.

The 555 is only good for a few seconds with small capacitors. For fun, someone invented a "programmable" 555 timer. You use a PC. It gets around some of the limitations. http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555C_Spec.pdf

I'll see if i can draw up a couple of schematics,

My first real analog design project was both complex and expensive. It was a biasable 4-terminal current-voltage converter for a lock-in amplifier. It had to have good AC performance which it did. It almost didn't work. I wasn't allowed to complete the DC design and there were two BIG problems:
#1: I had to isolate a capacitive load of our calibration devices.
#2. A few pA across 0V is a lot of offset. A real world issue.
His current version is at about 4 to 10 Hz so the cap on the 555 should be pretty small if a 100k to 220k resistor is used.
 
If it's an electrolytic cap, the tolerence is usually +80, -20%. metalized polyester, typical is -5%. You also have a potentiometer to adjust and you may have to adjust it as it ages too.

Like you said. It would not hurt to try both or three designs. The programmable 555 gets the cap smaller.
I found it hard to get a 1uf @ 50V and it was pretty big.

PS: I'm giving you a hard time.:)
 

MrSalts

Joined Apr 2, 2020
2,767
If it's an electrolytic cap, the tolerence is usually +80, -20%. metalized polyester, typical is -5%. You also have a potentiometer to adjust and you may have to adjust it as it ages too.

Like you said. It would not hurt to try both or three designs. The programmable 555 gets the cap smaller.
I found it hard to get a 1uf @ 50V and it was pretty big.

PS: I'm giving you a hard time.:)
The whole point is to trigger the submarine as soon as possible when the light turns off. Since the sub is non-retriggerable until the timer expires (until the light goes out) the 555 can be oscillating in astable mode as fast as we want (within reason but we can certainly try to push the limit to see what short pulse can be detected). It is completely possible that a 40kHz oscillator will retrigger the sub - the OP just has to try.

There is absolutely no reason to use a large cap or a programmable 555 with an extremely slow pulse rate.
 

MrSalts

Joined Apr 2, 2020
2,767
Your suggesting just free-run it. e.g. 5% duty cycle, 1 kHz. Not a pulse every 43s? An impatient person continually pushing the button.
No, that's not what I said. Run the 555 timer at 10 Hz (10 pulses per second works) so the maximum dark period is 0.1 seconds. I would propose that the OP can ramp up the frequency even higher to trigger - perhaps even 40kHz or more but that would be completely unnecessary as the dark period would be hard to see at 60 to 75 Hz. In any case, no need for long delays. Fast pulse trains work to retrigger.
 
@MrSalts Same deal, just the order of magnitude is off. Get it.
What would be a typical values of R & C? Too busy to figure it out.
What's the smallest physical size of the cap?
I was building a 4 secod timer, not witht he 555, but another obsolete chip and it;s hard to get a 2M pot and two 1uF 50V polyester capacitors. It was a one-shot and the period was RC for this timer. The 1uF caps have a lead spacing of 8mm. Now i can't even find them.
 

MrSalts

Joined Apr 2, 2020
2,767
@MrSalts Same deal, just the order of magnitude is off. Get it.
What would be a typical values of R & C? Too busy to figure it out.
What's the smallest physical size of the cap?
I was building a 4 secod timer, not witht he 555, but another obsolete chip and it;s hard to get a 2M pot and two 1uF 50V polyester capacitors. It was a one-shot and the period was RC for this timer. The 1uF caps have a lead spacing of 8mm. Now i can't even find them.
I would build it with an 0805 SMD ceramic 1uF cap ($0.20 for one, under 5 cents in quantity at Digikey). Pair that with Some 0805 resistors (10k and 47k). Done. The resistors can be soldered directly to the legs of a DIP - fold the leads over into a dead bug format and the whole thing is about the size of the dip-8 chip plus a NPN in TO-92 package.
 

Thread Starter

MFL

Joined Aug 13, 2021
41
I would build it with an 0805 SMD ceramic 1uF cap ($0.20 for one, under 5 cents in quantity at Digikey). Pair that with Some 0805 resistors (10k and 47k). Done. The resistors can be soldered directly to the legs of a DIP - fold the leads over into a dead bug format and the whole thing is about the size of the dip-8 chip plus a NPN in TO-92 package.
Hi MrSalts Missed checking the mail yesterday a bit.. but did finish the first working approach. :
IMG_5878_jpg.jpgIt all fits, "just" ... even the NPN.. and it's running at 32 hz Low time about 14ms .. Cap is 10 uf, R1 at 430, R2 at 2k ....what's all this talk about not lasting long! the "off" flashes can be seen .. but, are almost unnoticeable. If you blink, you will miss it.

I have an interest in the conversation between MrSalts & KISS .. I really should build other ways of doing this .. especially if this circuit is not going to last long !

Wiring diagram and parts list for,
System #2: where "A" is permanently shorted to ground.
System #3: where the LED current is monitored, and "A" is sent to ground when the current is below a threshold.

Both ideas are above my pay grade... For now... this thing is done, and will be installed in mineral oil ... what could go wrong.. :)
Lights ON.jpg

Thanks, big-time to both KISS and MrSalts
I have another of these models, and they are available on Amazon. .. while the above may serve as an example of "way too much work" .. your other ideas could come to pass ... with a little more instruction. Best Regards, Michael Lambert
 

MrSalts

Joined Apr 2, 2020
2,767
Hi MrSalts Missed checking the mail yesterday a bit.. but did finish the first working approach. :
View attachment 245946It all fits, "just" ... even the NPN.. and it's running at 32 hz Low time about 14ms .. Cap is 10 uf, R1 at 430, R2 at 2k ....what's all this talk about not lasting long! the "off" flashes can be seen .. but, are almost unnoticeable. If you blink, you will miss it.

I have an interest in the conversation between MrSalts & KISS .. I really should build other ways of doing this .. especially if this circuit is not going to last long !

Wiring diagram and parts list for,
System #2: where "A" is permanently shorted to ground.
System #3: where the LED current is monitored, and "A" is sent to ground when the current is below a threshold.

Both ideas are above my pay grade... For now... this thing is done, and will be installed in mineral oil ... what could go wrong.. :)
View attachment 245949


Thanks, big-time to both KISS and MrSalts
I have another of these models, and they are available on Amazon. .. while the above may serve as an example of "way too much work" .. your other ideas could come to pass ... with a little more instruction. Best Regards, Michael Lambert
Don't forget to check compatibility with the oil.

Also, instead of sending chocolates, make a donation to your local food bank.

Cheers!
 

Thread Starter

MFL

Joined Aug 13, 2021
41
Don't forget to check compatibility with the oil.

Also, instead of sending chocolates, make a donation to your local food bank.

Cheers!
Actually, I'm doing that today... Wife & I have a lot of Muscovy ducks.. and a lot of duck eggs .. we give them to the Food Bank in Fallbrook, CA. (weekly) You can still get chocolates if you get on my website and fill-in the contact form :) and if you tell me how to make the grounded point "A" work... :) .. In case it fails in a short time. I'll be happy with a few pictures and a video of it working .. the tank is a prototype demo .. I'm just going to install it & make waves.. the resulting pics will be posted here. by the way, how do you mark a thread here "solved"? Change the title?
 

MrSalts

Joined Apr 2, 2020
2,767
Actually, I'm doing that today... Wife & I have a lot of Muscovy ducks.. and a lot of duck eggs .. we give them to the Food Bank in Fallbrook, CA. (weekly) You can still get chocolates if you get on my website and fill-in the contact form :) and if you tell me how to make the grounded point "A" work... :) .. In case it fails in a short time. I'll be happy with a few pictures and a video of it working .. the tank is a prototype demo .. I'm just going to install it & make waves.. the resulting pics will be posted here. by the way, how do you mark a thread here "solved"? Change the title?
Just stop posting to the thread and it will sink to the bottom and be forgotten until some weird combination of words in a Google search motivates someone to post a better solution to it 10-years from now.

As for grounding A, I think an earlier post says it won't work. As in, if you connect A to ground then power it up, will it stay on or will it turn off after 20-seconds. If it stays on, great, no need for a 555 timer or transistor. If it turns off, your current design is the right one.
 

Thread Starter

MFL

Joined Aug 13, 2021
41
Just stop posting to the thread and it will sink to the bottom and be forgotten until some weird combination of words in a Google search motivates someone to post a better solution to it 10-years from now.

As for grounding A, I think an earlier post says it won't work. As in, if you connect A to ground then power it up, will it stay on or will it turn off after 20-seconds. If it stays on, great, no need for a 555 timer or transistor. If it turns off, your current design is the right one.
So far... it's working... must re-locate the wire so it's not visible... and erase a black sharpy line which I forgot to do duh...

Screenshot_8_25_21__7_38_AM.jpgIMG_0020_JPG.jpg
 
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