[Guide] Graceful shutdown switch without Pololu [RETIRED]

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hueblo
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Re: [Guide] Graceful shutdown switch without Pololu

Post by hueblo » Mon Aug 22, 2016 11:51 am

SidSilver wrote:
Camble wrote:@HoolyHoo The second diagram with the DMG switch shows the switch is in the off position. The EN pin is connected through the switch to the Drain pin on the JFET.

@hueblo The second diagram is the correct one. The pairs are: 3.3v & Shutdown. EN & Drain.

@SidSilver Nope, sorry.
Oh sorry I thought the tracks were vertical (because of the schematic)

The only thing that sux is the 2nd diagram did not even turn on the pi0 while the first one did. Also not sure what I'm doing wrong but as soon as I edit the monitor software it no longer boots.

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alien0matic
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Re: [Guide] Graceful shutdown switch without Pololu

Post by alien0matic » Tue Aug 23, 2016 8:25 am

hueblo wrote:
The only thing that sux is the 2nd diagram did not even turn on the pi0 while the first one did. Also not sure what I'm doing wrong but as soon as I edit the monitor software it no longer boots.
Since the script starts late in the boot process it can't be a software issue. If it doesn't even power on at all, the EN and GND pins are still connected or there is no powersource.

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Camble
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Re: [Guide] Graceful shutdown switch without Pololu

Post by Camble » Tue Aug 23, 2016 10:56 am

Guys, I've been having a few problems and thought I had maybe found a big problem with my schematic, which may have been causing people some serious problems in replicating this circuit.

When I was originally having issues designing this circuit, I was sure that the 100K pull-down resistor across the gate-source was the solution to my problems. However, I encountered more problems with the circuit when my PCBs arrived.

I had a bit of trouble replicating the problem on the breadboard, but have intermittently had issues since I finished designing the PCB. I've now had the same problem with the new surface mount components, the circuit was shutting off immediately instead of safely shutting down.

I was coming on here to post that the solution was to change the pull-down resistor for a pull-up resistor. This means that you would connect the 100K resistor across the gate-drain instead of gate-source. However, this is only working in some instances e.g. for my surface mount components. I can't get this to work for my TO-92 2N5460 JFETs.

Some of the datasheets for these JFETs state:

Code: Select all

Note:Source & Drain are interchangeable
I tested this a while back and it turned out not to be entirely true for this application. For this circuit, the JFET only works in one orientation. Other people have described similar symptoms so I'm hoping if you try switching the resistor over to the other side of the JFET, you may eliminate the problem.

So in summary: The Source still connects to Ground, and the Drain still to EN (via the switch), but the 100K resistor bridges the Gate and Drain. Give it a try, hope it works.

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Ganreizu
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Re: [Guide] Graceful shutdown switch without Pololu

Post by Ganreizu » Tue Aug 23, 2016 12:43 pm

Camble wrote:[spoiler="text"]Guys, I've been having a few problems and thought I had maybe found a big problem with my schematic, which may have been causing people some serious problems in replicating this circuit.

When I was originally having issues designing this circuit, I was sure that the 100K pull-down resistor across the gate-source was the solution to my problems. However, I encountered more problems with the circuit when my PCBs arrived.

I had a bit of trouble replicating the problem on the breadboard, but have intermittently had issues since I finished designing the PCB. I've now had the same problem with the new surface mount components, the circuit was shutting off immediately instead of safely shutting down.

I was coming on here to post that the solution was to change the pull-down resistor for a pull-up resistor. This means that you would connect the 100K resistor across the gate-drain instead of gate-source. However, this is only working in some instances e.g. for my surface mount components. I can't get this to work for my TO-92 2N5460 JFETs.

Some of the datasheets for these JFETs state:

Code: Select all

Note:Source & Drain are interchangeable
I tested this a while back and it turned out not to be entirely true for this application. For this circuit, the JFET only works in one orientation. Other people have described similar symptoms so I'm hoping if you try switching the resistor over to the other side of the JFET, you may eliminate the problem.

So in summary: The Source still connects to Ground, and the Drain still to EN (via the switch), but the 100K resistor bridges the Gate and Drain. Give it a try, hope it works.[/spoiler]
So basically buying your PCB is a safer bet than building it ourselves hahaha

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Camble
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Re: [Guide] Graceful shutdown switch without Pololu

Post by Camble » Tue Aug 23, 2016 12:49 pm

@Ganreizu Perhaps ;)

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Popcorn
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Re: [Guide] Graceful shutdown switch without Pololu

Post by Popcorn » Wed Aug 24, 2016 8:37 am

A show of hands? How many others have been able to get this circuit working? Wondering if you could take photos of your circuit. I really want this circuit to work but there's a couple of us that haven't be able to make it work yet. Wondering if it's something to do with my brand of JFET. I have Motorola brand.

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Re: [Guide] Graceful shutdown switch without Pololu

Post by alien0matic » Thu Aug 25, 2016 2:22 am

*raises hand*
Got it working, but it did cost me some time as the pinouts I found for the JFET didn't match the actual pinout of the JFET transistor I had. I made my own little circuit on a prototyping board. Looked through my fotos but I don't have one of the final board, sorry.

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Popcorn
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Re: [Guide] Graceful shutdown switch without Pololu

Post by Popcorn » Thu Aug 25, 2016 5:29 am

^^ Thanks! As an update, I eventually got the circuit working! But it's a damn weird configuration. Going to do some more tests with Camble and he'll probably report back with revisions to his guide.

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Re: [Guide] Graceful shutdown switch without Pololu

Post by BigOlTexasBoy » Thu Aug 25, 2016 11:17 pm

I'm trying to figure out Camble's Graceful Shutdown Switch and Popcorn's Low Battery Monitor using the DMG switch. Am I even in the ballpark with this?
Shutdown.jpg
Shutdown.jpg (33.29 KiB) Viewed 8346 times
I forgot to add the labels for the 47k resistor and the 2N3904 transistor.

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Re: [Guide] Graceful shutdown switch without Pololu

Post by alien0matic » Fri Aug 26, 2016 12:55 am

Regarding the tutorial it should be an 2n5460 JFET transistor. Don't know if you've misstyped it (two times) or got the wrong.

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