Meteor Resets – With Rottendog Solenoid Driver Board

(Topic ID: 229354)

Meteor Resets – With Rottendog Solenoid Driver Board


By oldschoolbob

31 days ago



Topic Stats

  • 134 posts
  • 13 Pinsiders participating
  • Latest reply 1 hour ago by G-P-E
  • Topic is favorited by 1 Pinsider

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  • Meteor Stern Electronics, 1979

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There are 134 posts in this topic. You are on page 2 of 3.
#51 10 days ago
Quoted from Quench:

The cap must be before Q1. It needs to filter the ripple coming out of the rectifier so the regulator circuits have a somewhat stable voltage source above regulation voltage. You can then omit the two 1000uF caps.
mbwalker, thankyou for your input. I don't think I explain things well sometimes so your response is very helpful

Thanks Quench, I enjoyed all you comments - keep them up. Other's had good comments too - don't mean to exclude anyone. Maybe we can tag-team w/Oldschool (and other people) and get things going. LOL.

Oldschool: Just a quick FYI. The two resistors I circled below on your schematic that went away... The LM323 is a 'fixed' regulator, meaning it's already set to 5V. Those resistors are essentially inside the part. You can buy these regulators as 'adjustable', and those two resistors are what set the desired output voltage. Say you wanted 6.3V instead of 5V. You would set those resistors for 6.3V. You can even use a variable resistor (a 'pot') if you wanted to turn a knob to adjust the voltage on the fly. Those resistors sort of serve the same purpose as your zener on the Q1 circuit.

- Mark
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#52 10 days ago
Quoted from mbwalker:

The two resistors I circled below on your schematic that went away...

oldschoolbob has copied the 5V regulator circuit from the Stern solenoid driver board power-supply section (see below) where those two resistors are used to slightly bump the output voltage up to around 5.3 volts. That explains why he has them there and where the support capacitor values came from

Stern_SDB_5V.jpg

#53 10 days ago

This my latest schematic (don't laugh - it took me all day to do this). But I see from Quench's post that I must move C23v to the left of R1. I'll get back to the other comments shortly.

Thanks

Bob

12 and 5 volt power supply r3 (resized).jpg
#54 10 days ago
Quoted from Quench:

oldschoolbob has copied the 5V regulator circuit from the Stern solenoid driver board power-supply section (see below) where those two resistors are used to slightly bump the output voltage up to around 5.3 volts. That explains why he has them there and where the support capacitor values came from
[quoted image]

Ahh..OK. Got it. makes sense.

Old school. You'll need to ditch the two resistors if you really want 5.0V as an output. I'd likely add a 100uF or 1000uF at the output. Depends on what you are using the 5V for. Keep the 0.1uF there tho. See below.

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#55 10 days ago
Quoted from oldschoolbob:

This my latest schematic

oldschoolbob, I would move the input section of the 5V regulator/components circuit to the output of the rectifier so the two regulator circuits are somewhat independent other than the bridge and C23. Just like you had it earlier.

#56 10 days ago
Quoted from Quench:

oldschoolbob, I would move the input section of the 5V regulator/components circuit to the output of the rectifier so the two regulator circuits are somewhat independent other than the bridge and C23. Just like you had it earlier.

I thought about that too, but I had mixed feelings.

Oldschool: I believe what Quench is concerned about is all the 5V current is now being supplied by the +12V regulator. So the +12V is doing double duty. The LM323 is good for 3A. If you try to draw 3A from the 5V plus whatever the +12V needs...could lead to a problem. Making numbers up, let's say the +12V is good for 4A and the +5V needs 3A. That only leaves 1A for the +12V output. Or the Q1 transistor is going to dissipate more power. A potential big problem. So the thought is move to +5V current away from Q1.

But there's actually a really good point to doing this way too (darn choices!). Let's look at why:

1) If you wire both the transistor and regulator to run off of the 17V , the LM323 now has to drop 12V internally (17V in - 5V out). Simple math: P=VxI. 12V times a possible 3A =36 watts the LM323 will dissipate! Ouch! You'll need a big heatsink. There is a way around this tho using a big resistor, if you are interested.

2) So if you run the 5V off of +12V, you only drop 7V across the LM323. 7V x 3A = 21 watts dissipated. Still likely toasty, but better. One huge benefit is the +5V regulator is now getting a really nice, clean, regulated +12V as in input. But as I mentioned above, now you potentially moved the problem to Q1.

Ugh, it's getting complicated! Make sense or 'clear as mud'?

I should ask...what currents do you want out of your supply and what do you want to power? How many amps is the transformer good for?

Edit: Also, the 10W 100 resistor near Q1? That only needs to be about 0.5W ish. Just using really rough calculations tho.

#57 10 days ago

Mark, thanks for stopping in. Can never have enough comments or teachers. And just because I have a scope doesn’t mean I know what I’m doing. Fortunately I didn’t have to pass a test to buy it. I’m 72 with no experience in electronics (career in construction) but I always liked electronics. Yes, Quench has always given great advice and he’s an excellent teacher. He explains things in simple terms that even I can understand.

A quick history – I built the original 12 volt power supply 40 years ago. Six months ago I added in the 5 volt section (copied from a Bally driver board) for testing MPUs. It’s worked great and I don’t want to deviate too much from this design. The main reason for building a new one is because it’s a rats nest inside. What I’m thinking is to rebuild everything I have on a single PC board to clean it up.

And before anyone suggests it would be easier (and probably cheaper) just to buy a power supply – I agree, but what’s the fun in that.

Thanks for the link to LTSpice. That’s sounds like something I’ll enjoy and maybe learn something. I’ll try it later tonight.

Quench, here’s my latest version with the 15,000 cap moved before the Q1.

12 and 5 volt power supply r4 (resized).jpg

Quoted from Quench:

I would move the input section of the 5V regulator/components circuit to the output of the rectifier so the two regulator circuits are somewhat independent other than the bridge and C23. Just like you had it earlier.

Well, back to the drawing board – no problem. Maybe I’ll apply for a job as an electronics engineer when I get this done. NOT.

By the way does the photo album work now?

https://photos.app.goo.gl/LcDp6v6B4QzjBjFP7

#58 10 days ago

Mark, that reminds me, Quench suggested I install fuses (probably a good idea) but I didn't know for sure where or what size. I'm guessing 3 amp fuses at the output side.

The existing transformer is 12.6 volts - 3 amp. The replacement I'm looking at is 12V - 4 A.

The transistor and regulator are mounted on heatsinks. I usually only use this for testing pinball boards and the heatsinks don't even get warm. However, I have used this for testing 12 volt 55 watt halogen bulbs before. That's over 4 amps and it worked OK.

Bob

#59 10 days ago

Thanks Bob, I'm really glad you're having a go and want to learn. I know you'd like to understand oscilloscope usage more - I'm not sure if you were watching that long Future Spa thread a month or so ago with the flickering lamps but an oscilloscope was critical in diagnosing the problem there.

Quoted from oldschoolbob:

Well, back to the drawing board – no problem.

Where did you connect the 5V regulator input to on the first upgrade 6 months ago?
mbwalker raised some valid points; my concern was more about simulating the early Bally/Stern power-supply circuit that you're trying to replicate. 5V and 12V both go to the MPU board on these systems and the 12V rail is used for timing the release of the CPU reset signal on power-up. 12V needs to reach its level after 5V has, otherwise the "valid power detector" circuit on the MPU board will release the CPU reset line before 5V is nominal/stable which we don't want. It will result in the CPU starting up unpredictably, typically with a locked/flickering LED. I'm afraid hanging the 5V regulator off the 12V regulator circuit will cause this.
I have seen the 12V rail in these Pinballs be as high as 17V. Typically they're around the 14.5 volt range.

A fuse is needed more on the 12V regulator since it has no circuit protection and currently your transistor heatsink is externally "live".
The LM323 has current limiting, power limiting and thermal shut-down.
Maybe mbwalker can suggest best fuse placement and ratings.

#60 10 days ago

Back before I added the 5 volt section I was using the 12 volt (regulated) supply to power a driver board - then connect the driver board to the MPU. (As shown back in post 16.) This worked really well but was a bit of a hassle to connect everything. So when I added the 5 volt section I wanted to replicate the same thing. That's why I'm leery of changing too much in this new design. After I added the 5 volt section it works great.

The first photo shows a red wire connected to the 12 volt output post and then to the 15,000 cap. (just like the Bally/Stern schematic) This is then connected to the PC board. If you look closely at the next photo you can see some green lines drawn on the PC board. This is where I cut away the copper cladding on the other side. (I didn't have any etchant). All the 5 volt components are on the PC board.

Having the 5 volt from the 12 volt regulated didn't seem to have any adverse effect when I used the driver board or with this new 5 volt addition.

This thing works so well I'm a little reluctant to make many changes. I don't even mind keeping the two 1000uF caps (but a single 2000 would look better). 2000uF caps seem to be difficult to find but GPE has 2200uf. Would that work as well?

Thanks

Bob

IMG_2917 (resized).JPGIMG_2920 (resized).JPGIMG_2926 (resized).JPG
#61 10 days ago

Here is my latest schematic. I’m pretty sure this is exactly what I’m using now. Except I omitted the diode on the 12 volt + and added the fuses. Everyone, please look this over and let me know your comments, questions, and suggestions. I really would appreciate it.

I need to get my parts ordered this week because GPE is closing down till next year.

Thanks

Bob

12 and 5 volt power supply r5 (resized).jpg
#62 9 days ago
Quoted from oldschoolbob:

Here is my latest schematic. I’m pretty sure this is exactly what I’m using now. Except I omitted the diode on the 12 volt + and added the fuses. Everyone, please look this over and let me know your comments, questions, and suggestions. I really would appreciate it.
I need to get my parts ordered this week because GPE is closing down till next year.
Thanks
Bob[quoted image]

Hi Bob,

Quench brought up some interesting points about how pin power supplies might need to come up in the correct order (one voltage before another). So keep that in mind.

You really should do a few things:

1) Put a fuse to the left of the bridge rectifier (the diodes). The transformer is by far the most expensive part in this supply, protect that. If it's a 3A then try to find a 2.5A fuse (if there is such a thing). If the bridge would go bad, there's nothing protecting the transformer from damage. You can remove the fuses on the right, but no problem leaving if desired. I'd be tempted to put one on the 120V side too in case a transformer winding becomes shorted.

2) The 2uF at the LM323. You really don't need that. The 0.1uF and the 15000uF have you covered. If you install, no harm whatsoever.

3) You NEED (capitalized on purpose to make a point) a fair amount of capacitance at the LM323 output. What happens is under a higher current draw, the charge is drawn out of that big cap and the regulator. But the big cap does all the heavy duty work at first (that's it's purpose, sort of like temporary battery). The LM323 takes a small amount of time to regulate (to get back to 5V) under a high load that happens quick. The large cap fills that void. By the time the large capacitor has drained it's charge, the LM323 has caught up and is supplying the current and at the correct voltage. WAG, at least a few hundred uF. If you don't do this, then you really have severely limited the performance of the 5V. With only a 0.1uF there, there's essentially no stored charge (no temporary battery). Under a quick, high current load, the 5V will dip for a short time, until it's internal circuitry catches back up. Again, at the risk of sounding redundant, a large cap at the LM323 resolves this issue.

4) Just a comment. You have some really large capacitors. For a very short moment, they will take a LOT of current to charge up. They act like a short when voltage is first applied. This can cause stress on the diodes, fuses, etc. The fuse size I mentioned might not be high enough, I just sized it to protect the transformer...not implying it's the right value. I guess the important part is to at least put something in there, then you can tinker with the value later.

Are you using thermal grease under Q1 and LM323? You need to, it aids in heat transfer, filling in the minor air gaps.

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#63 9 days ago

You mentioned you built your PS about 40 years ago, I think. I'm not too far behind you. Here's how I did it:

Two supplies. One fixed at +12V, other is variable. Similar regulators to the LM323. One was a LM317, the other a LM117.

I didn't use a PC board, I just hardwired to the sockets the regulators plugged into. The regulator are mounted on the other side of the metal plate, along w/a fuse on the primary (120V) side of the transformer. Had an old fan sitting around, so added that as an afterthought.

ps1 (resized).jpgps3 (resized).jpgps4 (resized).jpg

#64 9 days ago

Mark, thanks for the great advise.

The fuse before the rectifier is a great idea. How many times have we added fuses to Williams system 6 games before the rectifiers. (same thing). The new supply will have a new transformer – 12 volts 4 amps. I think a 3 amp fuse should work well here. I think I’ll leave in the 3 amp fuses on the output – can’t hurt. The old supply does have a 120 volt fuse in the back of the case. I was planning to install one on the new supply as well.

I thought the C24 cap was there because the regulator may be more than 4 inches from the filter capacitor. (See the datasheet info on Quench’s post 43). Also Bally/Stern has that cap on their driver boards.

The current draw on the 5 volt side shouldn’t be much. The only time I’ve used the 5 volts was to test MPU boards.

I just purchased a bunch of tubes of thermal grease. I always use it when installing heatsinks on rectifiers but for some reason I haven’t been using it for regulators. I guess I forgot. (And that stuff is messy.) I’ll remember to use it on the new supply.

That’s a great looking power supply. If mine was that nice inside I probably wouldn’t be rebuilding. I see you have 12 volts fixed and variable. Can you output 12 volts and 5 volts at the same time? Also where did you get the lettering on the front panel? Looks very professional.

Thanks

Bob

#65 9 days ago

Using the schematic in post 61, I started drawing the PC board layout when I noticed something. Looks to me like (electrically) point A and point B are the same. Point C and D are the same. And so are E and F.

R6a 12 and 5 volt power supply r6a (resized).jpg

To simplify the PC board layout I when back to change the schematic as shown below. When I was done I noticed the new schematic looks very similar to the one in post 57 - except the location of C1, C1a, and C23.

R7 12 and 5 volt power supply r7 (resized).jpg

Re-reading the posts, Quench suggested moving the input of the 5 volt section to the rectifier. As shown in blue marked up. But this isn’t how the old supply is built. The 5 volt section comes right off the 12 volt regulated output. I guess I could build it this way and if it don’t work, I could scrape off some copper cladding and add some jumper wires as shown in blue.

R7a 12 and 5 volt power supply r7a (resized).jpg

This sounded simple when I started but now I’m giving everyone a headache. I gotta get some rest.

Bob

#66 9 days ago

Oldschool,

You are right about c24, i was thinking that was the purpose of 0.1uF. The value varies between regulators, and 0.1uF was stuck in my head.

#67 9 days ago

Agree on the fuse before the rectifier - you can probably make it slow blow.

You've accidentally moved that F1 fuse from the 12V rail to ground. It must go back on the 12V rail.

I know you're not a fan of ebay buy you can get $1 LED display voltmeters from Asia which might be handy on the front panel - for eg:

ebay.com link

#68 8 days ago
Quoted from Quench:

You've accidentally moved that F1 fuse from the 12V rail to ground. It must go back on the 12V rail.

Just proves I shouldn't do this late at night.

I have these in my cart on Ebay.

ebay.com link » Digital Red Led Voltage Meter Dc 100v 10a Voltmeter Ammeter Blue Red Led Dual

Thanks

Bob

#69 8 days ago
Quoted from oldschoolbob:

Just proves I shouldn't do this late at night.
I have these in my cart on Ebay.
ebay.com link » Digital Red Led Voltage Meter Dc 100v 10a Voltmeter Ammeter Blue Red Led Dual
Thanks
Bob

That will sure spiffy up your 40 year old supply. Simple to hook up. See that 4-30V supply in the image? Hook that up to the output of your bridge. I think you measured that around 17V, right? Then the 'Current shunt'...put that on your '-' output. You'll need two, one each for 5V and 12V. But make sure the '-' supplies the 5V or the 12V separately, not both. In other words you have a common '-' for both 12V and 5V. Imagine the '-' being a 'Y' shape, and common for both 5V and 12V is the bottom of the 'Y'. The top of the 'Y', one side is the '-' for 5V. The other is the '-' for the 12V. The upper part of the 'Y' is where the current shunt goes. Make sense? You need to keep them seperate. I will draw if you want me too.

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#70 8 days ago

Like this.

But after thinking about this for a sec...say you had a mpu you were measuring that had a common ground for both +5 and +12V. You wouldn't be able to figure out how much current was +5V vs. +12V since there was only one ground for both.

You would have to put the current shunt in the + side of the output (might not be possible). That would mess up your voltage readings then.

Make sense?

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#71 8 days ago

Oldschool,

On your drawing...you need to move the cap too.

One more thing. If you don't have a load on the 12V line, Q1 will not turn on. There's no DC path to ground. Put around a 2K resistor across the 15000uF cap. That will allow a very small amount of trickle current to flow thru Q1 at all times. That will ensure Q1 is always turned on.

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#72 8 days ago

mbwalker, is there a reason you're suggesting to put the amp meter shunts on the common rail? Remember the common outputs will be connected together at the MPU board. I'd suggest the amp meters need to go on the positive rails.

#73 8 days ago
Quoted from Quench:

mbwalker, is there a reason you're suggesting to put the amp meter shunts on the common rail? Remember the common outputs will be connected together at the MPU board. I'd suggest the amp meters need to go on the positive rails.

I suspect they need to wired as shown by the vendor since the voltmeter part of that uses the current shunt as negative part of the volt meter. If you put the current sense on the + leg, then the yellow wire for the volt meter is at the same potential as the current sense. i.e. the black current sense would be at +12V, and the yellow is at +12V, hence, it would read 0V.

I agree tho, I'd prefer to put them on the + side, not sure if it supports it tho.

#74 8 days ago

Also, there could be a problem if the current sense black lead is also tied to the black lead (thru the PC board) of the 4-30V needed to run the display.

#75 8 days ago

Yes, there might be issues with the shunt having potential.

There's different examples of this same meter on Amazon with more wireups. Eg:
amazon.com link »

The current meter section may not be suitable here, not on both DC power supplies anyway.

[Edit] the description for the product says:
"The ammeter can be connected only to the negative of the device."

#76 8 days ago

Oldschool,

I redrew your schematic real quick. I think this was what you were after. Check that the values are the same as yours, I spent like 5 min drawing this in TinyCad..a free schematic drawing tool that is super easy. P.S. You really should add a bigger cap at the +5V output. It's standard practice.

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#77 8 days ago
Quoted from Quench:

Yes, there might be issues with the shunt having potential.
There's different examples of this same meter on Amazon with more wireups. Eg:
amazon.com link »
The current meter section may not be suitable here, not on both DC power supplies anyway.
[Edit] the description for the product says:
"The ammeter can be connected only to the negative of the device."

Looking at the ebay one, it makes sense what they did, just easier to measure current on the ground side and use that as part of the voltmeter too. Hey, not too shabby for not much change tho. Just limited in how to implement.

I believe 'high side' is the phrase that needs to mentioned in a search, that would imply the current could be measured on the hot side of the supply.

#78 8 days ago
Quoted from mbwalker:

I suspect they need to wired as shown by the vendor since the voltmeter part of that uses the current shunt as negative part of the volt meter. If you put the current sense on the + leg, then the yellow wire for the volt meter is at the same potential as the current sense. i.e. the black current sense would be at +12V, and the yellow is at +12V, hence, it would read 0V.
I agree tho, I'd prefer to put them on the + side, not sure if it supports it tho.

Adding to my post, this is what I suspected (from a EE blog):

"So I was tempted by the "too good to be true" price ($5 shipped) of these "0-999ma" ammeters from China on ebay. I snatched one up to use in a simple LM317 project I'm working on.
example: ebay.com link » 0 36 Blue Led Digital Dc Ammeter Amp Mini Current Panel Meter Dc 0 999ma
There are many listings for what appear to be the exact same ammeter, and some of them show them only in a low-side configuration, but one of them showed it in a high-side current sensing position.
Well, it turns out they are low-side only
I wired it up in this schematic: https://github.com/pepaslabs/DualLM317BenchSupply/raw/master/DualLM317BenchSupply_schematic.pdf
and stupidly hooked it up directly to a wall wart, instead of a current limited bench supply. It let out just a little bit of magic smoke before I unplugged it, and displayed "999".
Amazingly, it still worked when I rewired it into a low-side configuration.
So, buyer beware, these are low-side only."

So these can still be useful to Oldschool, he'll get nice voltage displays cheap, just won't know what the individual current are, just the total.

#79 8 days ago

Nothing wrong with adding two of these on the high side:

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#80 8 days ago

WOW! I didn't know adding a couple of meters would be so complicated. I just thought I could get a couple of meters and stick them in there to look professional. They really aren't necessary. I never looked at the wiring diagrams. I saw them on Amazon first and thought they would look cool. Then I found them on Ebay much cheaper. Are they both the same? Is there another meter you would suggest that's easy to install? Maybe I should just use a couple of volt meters.

I have a couple of old analog meters around but I like the digital.

Mark, thanks for the updated schematic (shows what can be done in a few minutes when you know what you're doing). I had the 15,000 cap on the 5 volt side because that's about what I have now. I'm not sure about the 2K resistor - there's not one there now but it works.

Thanks for the lessons guys.

Bob

#81 8 days ago

If I were to use my DMM to check amps, I would just cut into the + wire and put in my meter.

Why wouldn't this meter work the same way?

What's the purpose for the shunt?

Bob

meter (resized).jpg
#82 8 days ago
Quoted from oldschoolbob:

Sometimes I think the more I learn the less I know. But I do appreciate you taking the time to teach me. I hope there are others following this and they are getting something out of all this too.

I'm right here with you. Finding this pretty educational.
-Mike

#83 8 days ago

Glad your here Mike. Hope you learn something as I have. If you have any questions or comments just put them out there. These are great guys and they will be able to answer your questions.

I looked over the photos on the Ebay meter and they show this with no external shunt. Looks like is has a built in shunt. So what would be the problem hooking two meters up to to different voltages on the same negative side? See photos below. We have a common ground on the power supply board anyway.

Bob
V A meter 1a (resized).jpgV A meter (resized).jpgV A meter x2 (resized).jpg

#84 8 days ago
Quoted from oldschoolbob:

I looked over the photos on the Ebay meter and they show this with no external shunt. Looks like is has a built in shunt. So what would be the problem hooking two meters up to to different voltages on the same negative side? See photos below.

I was in the process of responding but you beat me to it regarding the internal shunt.

Quoted from oldschoolbob:

If I were to use my DMM to check amps, I would just cut into the + wire and put in my meter.

Yes.

Quoted from oldschoolbob:

Why wouldn't this meter work the same way?

The amp meter section wants to measure the voltage drop across the shunt. I guess it needs a reference point of 0 volts on one side because the meter itself is powered by an unknown voltage (users will hook it up anywhere from 4 volts to 30 volts supply).

Quoted from oldschoolbob:

What's the purpose for the shunt?

Think of the shunt as a very very low resistor. The more current going through it, the more the voltage drops across it. The amp meter is essentially measuring micro/milli volts drop across the shunt and converting it to a current readout.
That big external shunt is only supplied when you purchase the 100 amp model of the meter. The 10 amp model has its own shunt built in - see the picture below.

Quoted from oldschoolbob:

So what would be the problem hooking two meters up to to different voltages on the same negative side? See photos below.

The problem I see is that you will be connecting both 5V and 12V commons out of the power-supply together at the MPU board which will result in both shunts being connected directly across each other in parallel so you won't be getting different current readings from each amp meter.
Nothing wrong with hooking up two analog current meters on the plus side.

Volt-Amp_Meter1.jpg

#85 8 days ago

I said "If I were to use my DMM to check amps, I would just cut into the + wire and put in my meter." you answered "yes". Why can't we do that here?

The way I understand the shunt it's a very small resistor the makes about 10% of the current go through the meter.

Quoted from Quench:

Nothing wrong with hooking up two analog current meters on the plus side.

Wouldn't the digital meter work the same?

It's 6:30 AM here - I gotta get some rest.

I'll think about this in bed.

Thanks

Bob

#86 8 days ago

Since you are rebuilding your power supply you may want to consider a combination adjustable switch mode power supply and panel meter like this unit:

https://www.banggood.com/DPS5005-50V-5A-Buck-Adjustable-DC-Constant-Voltage-Power-Supply-Module-Integrated-Voltmeter-Ammeter-p-1062473.html?rmmds=search&cur_warehouse=CN

While I have not used that specific unit, it looks to be perfect for a home brew bench supply. You can set your supply voltage and a current limit which helps when you encounter a short circuit. Since this is a switch mode power supply, this unit will run much cooler than the series pass transistor linear design you have now. I have an old linear supply I built years ago like yours which some day I'll likely upgrade with a unit like this.

Additionally, I ran into a similar issue of measuring wrong voltages when bench testing a Flash Gordon (Bally) power / solenoid driver board. On that design, there was a power or ground loopback path which was completed through the wiring harness and MPU. If the MPU was unplugged, that loopback was broken, and the supply voltages I measured on the test pins were wrong. I thought my series pass transistor was fried, but after studying the schematics, discovered this path which connects through the MPU and manually connected it on my test bench and the supply was fine. I don't know if the Stern board has this issue, or if it is mitigated by grounding mods, but wanted to bring it to your attention. Good luck! Meteor is a great game.

PowerSupplyPanelMeterRuindeng_DPS5005 (resized).JPG
#87 8 days ago
Quoted from pinengineer77:

Since you are rebuilding your power supply you may want to consider a combination adjustable switch mode power supply and panel meter like this unit:

No doubt there are cheap and more efficient power-supplies around, but there is sentimental value in this power-supply oldschoolbob is using which he originally built a few decades ago and has served its purpose. This is a tidy up and upgrade.

Quoted from oldschoolbob:

I said "If I were to use my DMM to check amps, I would just cut into the + wire and put in my meter." you answered "yes". Why can't we do that here?
The way I understand the shunt it's a very small resistor the makes about 10% of the current go through the meter.
Wouldn't the digital meter work the same?

Your DMM has its own internal power and analog current meters are powered by the voltage across the shunt. i.e. they're independently powered.
These cheap volt / amp meters are being powered by your power-supply and to facilitate the simple no cost design they must have the shunt on the low (common) side.

From post #78, the EE blog fellow who hooked up the shunt connection on the high (plus) side had smoke coming out of the meter.
From post #75, the description for the product says: "The ammeter can be connected only to the negative of the device."

#88 8 days ago

Actually the device I posted is designed to be added to a home made power supply. It is very small (only a few inches square) and you mount it on your bench supply in place of a volt meter.

I understand the sentimentality, I still have the one I built ~40 years ago. Just pointing out that for under $30.00 you can take an old analog supply and upgrade it to be an efficient switcher and_ get a nice volt meter, current meter, programmable current limits, etc. It is worth checking out if you have not looked at these panels.

Good luck.

#89 8 days ago

Pinengineer, the display on that is awesome, more stuff on there than I'd know what to do with. And I like the simplicity - two wires in and two wires out. But it's big (about 2 inches X 3 inches). And it's adjustable - I can see me screwing something up by connecting it before I have it adjusted. Just connecting fixed 12 volts and 5 volts to the correct test points is dangerous for me.

I'm beginning to think this amp meter thing is getting too complicated. It would look neat but I don't think I really need it (or would even use it). I'm thinking now about just a couple of volt meters would do the trick. Something like these:

ebay.com link » Red Mini Voltmeter Dc 5v To 120v 3 Digital Display Voltage Volt Meter Led Panel

ebay.com link » 3pcs Dc 0 30v Red Led 3 Digital Display Voltage Meter Voltmeter Panel Motorcycle

ebay.com link » 1x Mini Red Blue Green Led Dc 0 100v Voltmeter Gauge Voltage Volt Panel Meter Us

Something just occurred to me - I always install a pilot light to indicate that the unit is on. Adding the meters would eliminate the need for a light.

Today I'm working on my PCB layout. We'll see how that goes.

Thanks

Bob

#90 8 days ago
Quoted from oldschoolbob:

I'm thinking now about just a couple of volt meters would do the trick.

I would skip the first ebay link, that volt meter wants 5 volts minimum so not useful to see when your 5 volt supply is low.

#91 8 days ago
Quoted from oldschoolbob:

Pinengineer, the display on that is awesome, more stuff on there than I'd know what to do with. And I like the simplicity - two wires in and two wires out. But it's big (about 2 inches X 3 inches). And it's adjustable - I can see me screwing something up by connecting it before I have it adjusted. Just connecting fixed 12 volts and 5 volts to the correct test points is dangerous for me.
I'm beginning to think this amp meter thing is getting too complicated. It would look neat but I don't think I really need it (or would even use it). I'm thinking now about just a couple of volt meters would do the trick. Something like these:
ebay.com link » Red Mini Voltmeter Dc 5v To 120v 3 Digital Display Voltage Volt Meter Led Panel
ebay.com link » 3pcs Dc 0 30v Red Led 3 Digital Display Voltage Meter Voltmeter Panel Motorcycle
ebay.com link » 1x Mini Red Blue Green Led Dc 0 100v Voltmeter Gauge Voltage Volt Panel Meter Us
Something just occurred to me - I always install a pilot light to indicate that the unit is on. Adding the meters would eliminate the need for a light.
Today I'm working on my PCB layout. We'll see how that goes.
Thanks
Bob

Hey Bob, I'm at work right, so no long answers...just use the volt meter part of what you bought. Will dicuss later.

#92 8 days ago

I haven't bought anything yet but everything is in shopping carts (4 vendors). Quench, I'm leaning toward the second meter - nice size, good price (3 for 9.99) and they're in the states.

Everything is in carts except for the Q1. I don't know what it is. There's no markings on it. I found one in my old parts drawer that I'm 90 percent sure it's the same. It has the same blue paint as the old one. Is there anyway to verify that they are the same?

Thanks

Bob

IMG_2883 (resized).JPGIMG_2887 (resized).JPG
#93 8 days ago
Quoted from Quench:

mbwalker, is there a reason you're suggesting to put the amp meter shunts on the common rail? Remember the common outputs will be connected together at the MPU board. I'd suggest the amp meters need to go on the positive rails.

It dawned on me today why the cheapie current meters are lowside. As an example, what if you tried to measure the current of a 200V motor and you stuck the current sense resistor on the hot side of the motor? Guess what, you now have 200V going to the little display module that might be running off of 5V...it's not going to be very happy.

But putting the sense resistor on the low side, one side is ground, the other is likely 10's of millivolts above that...now the display is perfectly happy. Low side takes any high side voltage out of the equation since it's barely operating above the ground potential. Problem solved.

Makes sense...that's why you can buy two for $7, lol.

#94 8 days ago
Quoted from oldschoolbob:

I haven't bought anything yet but everything is in shopping carts (4 vendors). Quench, I'm leaning toward the second meter - nice size, good price (3 for 9.99) and they're in the states.
Everything is in carts except for the Q1. I don't know what it is. There's no markings on it. I found one in my old parts drawer that I'm 90 percent sure it's the same. It has the same blue paint as the old one. Is there anyway to verify that they are the same?
Thanks
Bob[quoted image][quoted image]

Bob,

There's absolutely no way I'd stick that in there. Zero, nada, nope. Even if I was 99.9% certain...not going to happen. Please don't do that. We can probably find one for you to use, then just add to your order. I doubt it's even $2. It's not rocket science. I'll the explain the 2K resistor later, and you can still use your voltmeters too. You can still measure the current, you just won't know what's using the current - it will be the total of the +12 and +5V. Need to spend time with the wife for a while playing Houdini. Will check in later. I also skipped some postings - I'll get back up to speed reading those too.

-Mark

#95 7 days ago

Bob,

The 2K resistor. Absolutely not needed IF (capitalized on purpose) you have a load on the +12V. Ok, why do you need this? Warning, it will get a little complicated, and I don't expect you to really catch on to all this. But here it goes....a transistor (Q1) is a current controlled current source. Ok...fine, whatever. But in simple terms, it won't work without a load. You mentioned it worked before. Correct, because it had a load (i.e. maybe a mpu, light bulb, etc). Without out load, the transistor (Q1) won't be turned on. Even a voltmeter might be enough of a load. Regardless, it needs some sort of load otherwise the Q1 emitter has no path to ground. OK, ignore all that stuff I said - how do you resolve it? Simply add a resistor from the Q1 emitter to ground. The 2K resistor is barely anything, but it's enough to make the circuit work without anything else hooked up to it.

Gotta trust me on this, I don't like to toot my horn, but stick a resistor across the 15,000uF ranging from 2K to maybe 10K ohms.

#96 7 days ago
Quoted from oldschoolbob:

The way I understand the shunt it's a very small resistor the makes about 10% of the current go through the meter.
Bob

That gizmo you bought doesn't really measure current. It measures the voltage drop across a very small resistor. Using Ohm's law, they compute current by I=E/R.

For example, you are measuring the current of a light bulb. Say the current sense resistor is 0.01 ohms (really small). And the voltage measured across it is 10 millivolt. Using Ohm's law: 0.01 volts /0.01 ohms = 1 A. So they don't directly measure current, they just figure it using Ohm's Law. Also, all the current going thru the light bulb goes thru the current sense resistor

Like this:

Capture (resized).PNG
#97 7 days ago
Quoted from oldschoolbob:

...
Wouldn't the digital meter work the same?
...Bob

It does work the same way. But, and it's a BIG but, the digital meter is not tied to ground. It's doesn't know if there's 0.02V or 2000V volts on the path you are measuring. The current meter you bought from EBay is referenced to ground. That's the difference.

#98 7 days ago

Since you have an oscilloscope, if you REALLY want to measure current, then just buy one of these. Connects to the scope, and actually measures current, doesn't compute it on via Ohm's'Law. Much better than a meter. I own one, works fine.

Capture (resized).PNG

#99 7 days ago
Quoted from oldschoolbob:

WOW! I didn't know adding a couple of meters would be so complicated...Bob

Yeah, me and Quench blew up the thread without you!

And I did it again. Sorry about that, my time is limited. It's 'all or nothing' most the time. Trying to help when time permits.

#100 7 days ago

Mark, I appreciate the time you spend here. I know how valuable time is for a working man with family. (been there).

I saw that current clamp when I got my scope (it’s also Hantek). I figured I didn’t need it. Years ago I had a handheld clamp meter – I lost it somewhere but I never missed it.

I decided the best solution for the amp meter is not to use one on here. I don’t think I really need it anyway (they just looked cool). I will install a couple of volt meters – should look just as cool.

On the addition of the 2K resistor. Quench said a while back that he sometimes has problems with his computer power supply (something about the VR1 being out of spec) If he manually resets the MPU it will start up fine. I’ve never had that problem with this supply. Maybe (just maybe) it’s because my 12 volt is not fully energized until it sees a load. I really don’t know, but maybe Quench or someone could give an explanation. For this reason, I’m a little reluctant to add it at this time.

By the way, how was the date with your wife. Did you guys have a good time?

Thanks

Bob

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