Questions about my DIY Launch Controller

Voyager1 said:

My panels were simply mounted on 10 mm Aluminium angle, as shown in the images below. There are small extrusions near the top of the inside of the case that the angle sits on. I just cut the appropriate lengths of Aluminium and glued them in place with 5 minute epoxy. I then drilled and secured them with self-tapping screws. Cheap, easy and solid.

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The cases I prefer from SERPAC include the ability to mount a plate. They even sell blank aluminum plates for them. But you can get something custom machined from Front Panel Express for about the same price.

BrainlordMesomorph said:

Thank you.
I'm certain you think that's "surprisingly easy" and that I should try it.

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It really is easy. I did my first PCB when I was 12 and was for an FM transmitter. Trust me

BrainlordMesomorph said:

On another note. please explain grounding:

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Good question. Using a ground symbol is usually done in circuits to indicate what is nominally the 0V or battery return line. Using the symbol means the schematic is less cluttered with lines and easier to read. It doesn't make much difference on simple circuits but as they get more complex the ground line, if it is drawn, really muddies the schematic and makes it more difficult to read. This means it is easier to make a mistake during design, layout (manual) and faultfinding.

OverTheTop said:

Good question. Using a ground symbol is usually done in circuits to indicate what is nominally the 0V or battery return line. Using the symbol means the schematic is less cluttered with lines and easier to read

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That's exactly what I meant by graphical shortcut. And thanks for the answer guys. But I must say as a layman who struggled to understand electronics his whole life, I have to say (sarcastically) "thanks guys" to the entire electronics industry! For years I've looked at schematics and said to myself "Grounded? How is this grounded? Its a pocket radio!)

You guys really need two different symbols. At one point I was an architectural draftsman. Architects would never use the same symbol for a wire and a copper pipe driven 20' into the ground.

Can I at least assume that electronically it is the same? Could I actually use two grounding steaks instead of a return line on a DC circuit? (and if the answer is no then no wonder I never understood electronics.:/)

Voyager1 said:

My panels were simply mounted on 10 mm Aluminium angle, as shown in the images below. There are small extrusions near the top of the inside of the case that the angle sits on. I just cut the appropriate lengths of Aluminium and glued them in place with 5 minute epoxy. I then drilled and secured them with self-tapping screws. Cheap, easy and solid.

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So you drilled though the sides of the case? (violating the watertightness) I was trying not to do that. No particular reason. Just I live in Florida, things end up in canals. (I once swam halfway across a river with $1000 worth camera gear safely in a Pelican case.) But that does look a lot more professional than my wood.

BTW: from what I've read, the epoxy won't stick. its the screws that are holding that together. You could have just taped them into position while drilling and screwing.

You moving to the larger case has given me pause.

I have that same larger case, too (in yellow). I had thought that would have plenty of space in the lunchbox sized case, but it is stuffed! I have to put the batteries on their sides, and they fill the bottom. (I always underestimate the size of the components behind the control panel.) and I did want this thing to be upgradable, so now I'm thinking of the larger case.

Which means I would have to totally rethink my control panel....
like I said, I have pause.

BrainlordMesomorph said:

You guys really need two different symbols. At one point I was an architectural draftsman. Architects would never use the same symbol for a wire and a copper pipe driven 20' into the ground.

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There are at least three variants on the ground symbol for circuit common, chassis, and Earth ground.

UhClem said:

There are at least three variants on the ground symbol for circuit common, chassis, and Earth ground.

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Oh, some minor nuanced difference to the symbol I'm oblivious to?

And let me rephrase myself, Architects would never use even slightly similar symbols for a wire and a copper pipe driven 20' into the ground.

BrainlordMesomorph said:

Oh, some minor nuanced difference to the symbol I'm oblivious to?

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https://www.rapidtables.com/electric/Ground_Symbols.html

The most frequently used symbol is the one for Earth ground. But no one expects an actual connection to Earth for the average circuit.

Usage does depend on what symbols are available in your CAD package. The one I use just had the one. I added the symbol for circuit ground and I am trying to remember to use it.

Also keep in mind that a schematic just shows (typically) how things are connected together. It does not show the physical routing of the wires. For example in these circuits you need to use large wires for the high current portions but don't need it for LEDs or other low current portions.

BrainlordMesomorph said:

That's exactly what I meant by graphical shortcut. And thanks for the answer guys. But I must say as a layman who struggled to understand electronics his whole life, I have to say (sarcastically) "thanks guys" to the entire electronics industry! For years I've looked at schematics and said to myself "Grounded? How is this grounded? Its a pocket radio!)

You guys really need two different symbols. At one point I was an architectural draftsman. Architects would never use the same symbol for a wire and a copper pipe driven 20' into the ground.

Can I at least assume that electronically it is the same? Could I actually use two grounding steaks instead of a return line on a DC circuit? (and if the answer is no then no wonder I never understood electronics.:/)

So you drilled though the sides of the case? (violating the watertightness) I was trying not to do that. No particular reason. Just I live in Florida, things end up in canals. (I once swam halfway across a river with $1000 worth camera gear safely in a Pelican case.) But that does look a lot more professional than my wood.

BTW: from what I've read, the epoxy won't stick. its the screws that are holding that together. You could have just taped them into position while drilling and screwing.

You moving to the larger case has given me pause.

I have that same larger case, too (in yellow). I had thought that would have plenty of space in the lunchbox sized case, but it is stuffed! I have to put the batteries on their sides, and they fill the bottom. (I always underestimate the size of the components behind the control panel.) and I did want this thing to be upgradable, so now I'm thinking of the larger case.

Which means I would have to totally rethink my control panel....
like I said, I have pause.

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Yes, we have several symbols for different ‘grounds’: signal, power, chassis, earth, digital, etc.

I wasn’t concerned about watertightness for my case.

Yes, epoxy is not good for a long term adhesion to that plastic, but was fine for the brief period I needed it to hold the Aluminium strips while I drilled and screwed them.

BrainlordMesomorph said:

Oh, some minor nuanced difference to the symbol I'm oblivious to?

And let me rephrase myself, Architects would never use even slightly similar symbols for a wire and a copper pipe driven 20' into the ground.

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Yeah, but architects would totally design a thing that's physically impossible and also unmaintainable. It's almost like there's subspecialties....

UhClem said:

https://www.rapidtables.com/electric/Ground_Symbols.html
The most frequently used symbol is the one for Earth ground. But no one expects an actual connection to Earth for the average circuit.

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Ah, so you admit that you're deliberately using the wrong symbol.

BrainlordMesomorph said:

Ah, so you admit that you're deliberately using the wrong symbol.

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No.

When I learned electronics this was the symbol commonly used. I dug up an early reference and my copy of "The Forrest Mims Engineers Notebook" (from 1979) uses this symbol throughout. Even though no connection to Earth was ever intended or even suggested.

At some point (I have no idea of its history) this other symbol for circuit ground appeared. So while I am used to the original symbol and know what it means, I am trying to overcome decades of inertia and trying to remember to use this newfangled symbol.

UhClem said:

No.

When I learned electronics this was the symbol commonly used. I dug up an early reference and my copy of "The Forrest Mims Engineers Notebook" (from 1979) uses this symbol throughout. Even though no connection to Earth was ever intended or even suggested.

At some point (I have no idea of its history) this other symbol for circuit ground appeared. So while I am used to the original symbol and know what it means, I am trying to overcome decades of inertia and trying to remember to use this newfangled symbol.

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Ah, so you admit that you're deliberately using the wrong symbol.

Please understand that as a layman struggling with electronics, that the inconsistent use of the ground symbol has been one of the things baffling me.
(and it was avoidable)

also this question went unanswered:

Can I at least assume that electronically it is the same? Could I actually use two grounding steaks instead of a return line on a DC circuit?
is that where that comes from?

lastly, for my DC circuit inside a plastic box (i.e. no "chassis") signal ground is correct?

BrainlordMesomorph said:

lastly, for my DC circuit inside a plastic box (i.e. no "chassis") signal ground is correct?

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I would use the one I used in my circuit above, as it is the default that is normally used. You can use the signal ground if you like to.


The single bar GND, or the inverted Christmas tree are probably the most common. I would not use the "earth" symbol for anything but a chassis earth point (functional or protective, but I won't go there ) or an earth stake on a house maybe. Sometimes we need more than one ground. There might be a power ground for motors, a signal ground for some analog amplifiers, and maybe a digital ground as well all on the same circuit. The usual symbols are normally used, with the addition of annotation to show which particular ground you are talking about. They usually all get reconciled together at some point. This point is chosen so things like large motor currents don't affect sensitive electronics.

Ground or earth is such a can of worms if you want to get into the details...

As for fixing inside a Pelican case, you can mount a sheet of aluminium with some suitable double-sided tape. Everything else mounts off that. The large area of the plate means good solid bonding to the case. You will need to select a tape that is compatible with the material of the case. I am sure 3M have a really good tape for your needs. Check to see if one of the VHB range is compatible with Pelican plastic.

BrainlordMesomorph said:

also this question went unanswered:

Can I at least assume that electronically it is the same? Could I actually use two grounding steaks instead of a return line on a DC circuit?
is that where that comes from?

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We eat steaks and drive stakes. [emoji39]
The answer to your question is a qualified yes, usually. That’s why you get electrocuted when you touch a high potential wire. Different soils work differently as grounds. Also, a wire stretched from one ground rod to another will sometimes experience ground currents because the potential of the earth is different in different places. It’s all relative.

OverTheTop said:

I would use the one I used in my circuit above, as it is the default that is normally used. You can use the signal ground if you like to.

View attachment 357582
The single bar GND, or the inverted Christmas tree are probably the most common. I would not use the "earth" symbol for anything but a chassis earth point (functional or protective, but I won't go there ) or an earth stake on a house maybe. Sometimes we need more than one ground. There might be a power ground for motors, a signal ground for some analog amplifiers, and maybe a digital ground as well all on the same circuit. The usual symbols are normally used, with the addition of annotation to show which particular ground you are talking about. They usually all get reconciled together at some point. This point is chosen so things like large motor currents don't affect sensitive electronics.

Ground or earth is such a can of worms if you want to get into the details...

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This is hilarious.

This page show those same symbols, labeled the other way.
https://www.rapidtables.com/electric/Ground_Symbols.html
They show the christmas tree as earth, and the pitchfork as chassis ground. (and I've seen the pitchfork chassis ground before in car repair manuals)

it is kind of reassuring to me every time I discover that something that has been confusing me for a long time, turns out to not be me just being dumb. But rather something that is actually just inconsistent and confusing by its nature.

I had reached the point where, from usage, I was sort of guessing that what it meant. But the deadly importance of properly grounding AC circuits and antenna has been drilled into me since I was a kid, and I really didn't feel comfortable GUESSING about something of DEADLY importance. ("Yes, you should never consume poison, and this is labeled poison, but in this case, I don't think they really mean it....")

Steve Shannon said:

The answer to your question is a qualified yes, usually. That’s why you get electrocuted when you touch a high potential wire. Different soils work differently as grounds. Also, a wire stretched from one ground rod to another will sometimes experience ground currents because the potential of the earth is different in different places. It’s all relative.

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Thank you that makes sense.

Steve Shannon said:

We eat steaks and drive stakes.

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I don't eat meat.

BrainlordMesomorph said:

I don't eat meat.

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Well, there’s your problem …

(Not really of course; although most of us engineers seem to enjoy a good steak)

You can drive a stake into a steak.

Back to symbols, they are there to make the schematic more readable and reduce confusion. If you want to get confused start looking at the international product safety standards and how they treat earths. There can only be one protective earth on the whole product, the rest are functional. They even regulate how the symbol is drawn. https://incompliancemag.com/article/the-grounding-symbols/

For you I suggest using the upside-down Christmas tree symbol and thinking of it as zero volts (0V). Simples .

OverTheTop said:

For you I suggest using the upside-down Christmas tree symbol and thinking of it as zero volts (0V). Simples .

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Not 12V- or just V-?

I would personally call it and think of it as 0V. -12V (or variants) is actually 24V away from 12V (+ is implicit). Imagine two 12V batteries connected in series, and calling the center zero volts. You have +12V on one battery, -12V on the other, and a total of 24V between -12V and +12V.

Remember the aim is to stick to conventions sometimes to avoid confusion in others'. You might have it straight in your head in that (12V-) situation but it will confuzzle other people. Clarity in communication is the aim for schematics.

OverTheTop said:

I would personally call it and think of it as 0V. -12V (or variants) is actually 24V away from 12V (+ is implicit). Imagine two 12V batteries connected in series, and calling the center zero volts. You have +12V on one battery, -12V on the other, and a total of 24V between -12V and +12V.
Remember the aim is to stick to conventions sometimes to avoid confusion in others'. You might have it straight in your head in that (12V-) situation but it will confuzzle other people. Clarity in communication is the aim for schematics.

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Here’s another example. In electric substation controls, the voltage used by controls is -125 Vdc. The other side is tied to ground, a real earth ground with a large ground mat to provide a common ground for all devices.

Here is a another forum’s discussion to help you understand the idea of ground, earth and 0V.

https://www.physicsforums.com/threads/what-does-0-v-exactly-mean-in-an-electric-circuit-mean.803356/

How to safely discharge a battery?

I want to test recharger system, but it looks like the batteries came fully charged. Should I wire up a light bulb?
what's the fastest, safe way to use that up?

Voyager1 said:

Here is a another forum’s discussion to help you understand the idea of ground, earth and 0V.

https://www.physicsforums.com/threads/what-does-0-v-exactly-mean-in-an-electric-circuit-mean.803356/

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That's a read.
"Ground exists only in the mind of the person analyzing the circuit"

I'm going back to bed now.

BrainlordMesomorph said:

How to safely discharge a battery?

I want to test recharger system, but it looks like the batteries came fully charged. Should I wire up a light bulb?
what's the fastest, safe way to use that up?

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Light bulb sounds like a great idea. If you are using LiPo batteries don't take the voltage below 3.6V per cell or you will kill the battery.

OK what does this mean?

I build the circuit just as loose parts on the bench. (Can I call it a bench? technically its a desk) Lights flash, beeping beeps.

I hook up my multimeter, as you might guess from my level of electronics education, I use this very occasionally for continuity testing, and measuring DC volts. That 's about all I know how to do.

So with the multimeter in the place of an igniter, I turn this thing on.

Continuity Test reads at 0.015 A. and a light and a nice loud beep. (OK)
I switch on the high power circuit, press the big red button and pop the 10A fuse.

What does that mean?

BrainlordMesomorph said:

OK what does this mean?

I build the circuit just as loose parts on the bench. (Can I call it a bench? technically its a desk) Lights flash, beeping beeps.

I hook up my multimeter, as you might guess from my level of electronics education, I use this very occasionally for continuity testing, and measuring DC volts. That 's about all I know how to do.

So with the multimeter in the place of an igniter, I turn this thing on.

Continuity Test reads at 0.015 A. and a light and a nice loud beep. (OK)
I switch on the high power circuit, press the big red button and pop the 10A fuse.

What does that mean?

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It means you misused your multimeter and the fuse blew rather than the meter. You don’t want continuity or current settings to test the launch circuit; that dumps as much of the battery’s current as possible.
The good news is your circuit works.