Hi Sarge;
Thanks for the tip, will do.
Appreciate the "regulated" advice.
Will be back when I have it further along, etc.....
Oxbo

 

Am looking at this one, it doesn't say "Regulated" but I searched the website for regulated and this was listed as one, etc.
Your feedback appreciated.......
http://www.mpja.com/prodinfo.asp?number=16741+PS

 

Yes, that's a regulated supply. Price isn't bad either

You'll need to put it in an enclosure, of course.

 

10-4, Tx's........

 

OK , being somewhat on the lazy side, re-looked and decided on this one..
http://www.mpja.com/prodinfo.asp?number=16001+PS
Is a bit more expensive, but, is switching and regulated (read up on Wiki).
Obviously, I decided on it so that I didn't have to take the time to fabricate an enclosure.
I see the terminals (360 view) say ->
"L" = line (Black wire)
"N" = Neutral ((White wire)
"Gnd symbol = (Green wire)
Then,
It offers a "-V" and a "+V"
The description doesn't say anything about a "-V"
Could you offer an explanation as to what they are refering to
with the "-V" terminal.
I'm sure once I get hold of the schematic it'll explain it, etc..
Just wondering.........

 

MPJA's site is down at the moment, so I can't see it.

 

OK, finally got to see it.

The output side of the supply is probably completely isolated from the input side.

This would allow the end user to reference the output to an arbitrary voltage level.

If you wanted to, you could connect -V to the ground terminal and your board's ground. Then use the +V terminal to supply +12v.

Note that you will still need to fabricate some sort of cover for the terminals, so that young fingers couldn't touch the line and neutral terminals, which are exposed.

 

That sounds good.
The power supply will be enclosed inside the enclosure, behind the LED board (which is itself bolted securely at it's top).
Across the front of the enclosure will be a 1/8th " clear piece of lexan which fits in the 3/16ths slot on the front (made from "F" channel).
It is installed by dropping it in from the top then replacing the top piece ("F" channel) and securing that piece with nine sheet metal screws, etc.
I think that will qualify as safely enclosed.
But, I defer to your opinion..........

 

That'll work.

What about ventilation? You will need a way for air to flow through it to keep things cool. It won't be a lot of heat, but if there is no ventilation, the heat will eventually build up inside and tend to cause things to fail.

 

Hmmmm,
Gotta install a fan I guess......

 

Simple holes in top and bottom will likely work, but the hot air has to be allowed to escape, otherwise it is an oven.

 

Hi Bill;
How's things ?
I always read the forum, keeping up with you guys.
Most of it is way over my head, one day I'll finish this project and be able to
try something else, then again, might take a few years off, LOL !
Is one thing playing with making schematics on the computer, and even the breadboard, then, ya gotta do the grunt work, actually make the darned thing.
But, when it's all over ya can stand back and be proud of the accomplishment
(with fingers crossed behind your back that it'll keep on working) LOL.
I think, with all I've got going in this thing, will be a simple matter of installing a fan and some air holes, no big deal.
However, I didn't do anything for ventilation on the "console", so, sure need to go and at least put some holes in it.
At the moment my son has it and is supposed to be putting on the labeling
for the buttons/switches, and, he's procrastinating to the n'th degree.
Can't understand that fellow, he's got a college degree and a good job (coach at a high school) but he never has been a finisher. He starts projects (at home) but haven't seen the fellow finish one single thing.
That's probably the worst fault one could have, other than drugs/crime, etc......
Better just count my blessings, etc.....
Have a nice day !
Oxbo

 

OK;
Attached are the two circuits I propose for my big board LEDs.
For the DP (decimal points/colon), as I did with the console, just tied cathodes to ground and they stayed lit, which is what I wanted.
Recalling, the data from the kit segment LEDs was tapped off and fed to the buffer board (ULN2004A for the drive transistors) (ULN2804 used for the cathodes). From there the data travels through the 10ft cable to the big board, as shown in the attached pics.
I took Sgt Wookie's advice and made R1 and R2 values within the ranges he suggested.
However, I'd sure like to know how one "figures" those values, am still not sure that these figures are the best that can be.
I look at the graphs on the data sheet (MPSA64) and just get lost, etc.
Like, seems like I'm going to have a large amount of Ib, but, am just guessing. Tried to measure Ib with my multimeter but it doesn't register anything, guess it doesn't go that low (ua's)....
Tx Yu for any enlightenment.......
Oxbo

 

One technique that is used to figure R1 and R2 is to calculate the Thevenin's equivalent resistance and the Thevenin's equivalent voltage. Then using these two values you can compute the base current. With the base current in hand you should be able to use the nominal value for the transistor's beta to determine the collector current.

Of course you need to take into account the Vbe of the transistor in computing the base current.

hgmjr

 

On closer examination of the PNP darlington pair circuit, it would appear that the transistor driver is being over-driven in the extreme. Where did you come by the values that you are using?

hgmjr

 

Yes, you are overdriving the base.

For R1, use 220k.
For R2, use 47k.
That's still a considerable amount of overkill, but it'll work just fine for both of them.
For the DP, use 360 Ohms for R3.
For the segments, use 120 Ohms for R3.

 

Yes, you are overdriving the base.

For R1, use 220k.
For R2, use 47k.
That's still a considerable amount of overkill, but it'll work just fine for both of them.
For the DP, use 360 Ohms for R3.
For the segments, use 120 Ohms for R3.

This helps greatly.
However, there isn't a formula or some way
that I can figure out these values by myself rather than have someone just telling me what I need ??
I'm sure the answer is found in the graphs (MPSA64 datasheet).
hgmjr- Appreciate the suggestion (Thevenin's Theorium) but all that figuring and I "Know" I'd wind up out in left field, far out there
Lets see, how about the theory of Ib being 1/10th of Ic? I'll investigate that and see where it leads me, but, will hold on to these values Sarge has offered as biblical literature, as always, he's a wealth of knowledge.
Tx's guys..........
Oxbo
P.S. - Oh ! I just won a bid on E-bay for a "Simpson 260", should be in the mail, hope it is in great shape.......

 

I wish you luck for this. I designed something similar, fairly complete, but never built it. Mine was for a Combat Robotics arena.

 

....

Lets see, how about the theory of Ib being 1/10th of Ic? I'll investigate that and see where it leads me, but, will hold on to these values Sarge has offered as biblical literature, as always, he's a wealth of knowledge.
Tx's guys..........
Oxbo
.......

The Ib = Ic/10 is more applicable to a single transistor stage. What you have here is a darlington pair. That means that the effective beta is the product of the beta of the two transistor. In this case you would be better served if you think in terms of Ib = Ic/100.

hgmjr

 

Is Thevenin's Theorem not in your comfort zone? If it is not, you can review the subject in the AAC ebook.

hgmjr