EEVblog #801 - How To Design A Digital Clock

[linux-works]

Used to be true, but now most have decided that they will allow a certain number of cycles slippage with heavy load and will not recover them at night with low load. You might be lucky in that you only lose a few seconds per month, but they pretty much decided it was too expensive to get the controllers to aim for midnight on the master clock to agree with UTC.

Kitchen clocks all used to run on the mains to keep time in the UK, but then cheap batteries and 32.768kHz crystals took over. Later we had accurate clocks using radio broadcasts for synchronisation. Now it's NTP.

more and more, its GPS.  or some other IoT message transfer protocol that includes 'time' as a reportable variable

OT: I should dig up my own binary led clock that I built as a kid (late 70's).  I was given a handful of point source red and green leds and I used 7490's (etc) to show HH:MM:SS in red and green groups of those pt-src leds.  it had a funky 'use what you can find in a craft store' look for the chassis, too.  and it did use the local 60hz for its timebase; I supplied a wallwart with 9v ac into it, used a 7805 and local bridge/cap to create dc.

if seen today, it might be scary to someone who didn't know; but for those who could not understand binary, whether it was currently counting UP or DOWN would be totally lost on them

if I find the clock in my storage boxes, I'll snap some photos of it.  I built it when I was late teens and I'm over 50 now, so its been in storage for a long time..

[AF6LJ]

Dude, whether it is possible or not is irrelevant. Conspiracies are being stated as fact. On one had, the conspiracy nutters are saying well he didn't design anything and just disassembled a clock and reassembled in another receptacle to discredit him technically.

First off I am not a DUDE, I am female. Perhaps you should check people's profiles once and a while.
And no I am not going to address your comment, not worth the bandwidth here.

Firstly, in Australia dude is regularly used as a general reference without implying gender. No need to get your knickers in a knot.

Okay I can accept that, even though it may be considered impolite, that's okay there are a number of cultural differences between AU and US.

What you have stated so far is no more than an unproven conspiracy.

Perhaps; but consider what we don't know about the story.
Far too many details missing to rule out any one source of information at this time.

And you have evidence the clock was only disassembled? please lets see it.

You don't seem to understand how this works. You are making claims without evidence, the impetus is on you to prove it - not for others to prove the negative assertion. This is basic stuff (something which conspiracy theorists and 'truthers' tend not make a mistake with.

When you have provable facts please come back with them and their sources.

I'm not the one making a claim - it is up to you when saying something is true to back it up. I am simply questioning the claims - it is not up to me to provide evidence that it isn't true. That isn't how it works.

So that's the point, if you make a claim, it is up to you to prove them with evidence. Not for me to provide evidence otherwise.

I get that but it needs to be applied all the way around, including to those stories you and others like Dave favor.
One related thought;
The difference between a skeptic and a debunker is a skeptic is always after the truth, a debunker could care less about the truth when it doesn't fit his or her agenda.
I am the skeptic. And for now I am done with this urinating contest, I have better things to do like get on the radio and talk to my friends in Northern Kalifornia.

[EEVblog]

Firstly, in Australia dude is regularly used as a general reference without implying gender. No need to get your knickers in a knot.

Okay I can accept that, even though it may be considered impolite, that's okay there are a number of cultural differences between AU and US.

Another example: I call girls "guys" all the time. If I see a bunch of girls I know I go "hi guys". Guys is just the common collective term.

What you have stated so far is no more than an unproven conspiracy.

Perhaps; but consider what we don't know about the story.

Why are people unable to simply leave it at that?
This whole thing has bought out the worse in people, it's embarrassing.
When I first released the video and that blog post about the clock being a Radio Shack thing hadn't been posted yet, almost everyone was in support of Ahmed.
But then suddenly it went viral that it wasn't his design (even though that was obvious and even he said it was a 10-20min job), and the world went ape shit and turned on him. As if it's the greatest fraud in history that a 14yo kid overated his skills and used the wrong word to describe what he did.
And people accuse me of being manipulated by the media 

Far too many details missing to rule out any one source of information at this time.

You have zero sources of information that confirm your assertion.
You and others just want to ride the Ahmed hate train because *insert reason here*

So that's the point, if you make a claim, it is up to you to prove them with evidence. Not for me to provide evidence otherwise.

I get that, but

No, you don't get it. There is no but. You made a claim, you provide the evidence, or you get rightfully get shot down in flames for it.

but it needs to be applied all the way around, including to those stories you and others like Dave favor.

The only story I favor is giving a 14yo electronics hobbyists the benefit of any doubt. I'm guilty as charged.
If it turns out all the conspiracy stuff is all true, so be it. People can say "I told you so" all they like, they will still be the ones who were too pathetic enough to give a 14yo kid the benefit of the doubt.

The difference between a skeptic and a debunker is a skeptic is always after the truth, a debunker could care less about the truth when it doesn't fit his or her agenda.
I am the skeptic.

No, you are not. You have stated certain facts as being, and I quote you "all factual.". When pressed for evidence for that statement you haven't giving any. An agenda if there ever was one!

Many people know my strong thoughts on religion, Islam, and you can likely guess what I think of Ahmed's father, and yet I still support Ahmed - why?
Well, I can either give up on a 14yo kid and join the whole world in chorus about how he's a "fraud", and crap on about his family ties etc, but how is that going to help him?
Why are so many people now willing to throw a 14yo kid to the fire?
This story has turned an order of magnitude sader than I thought it was at the beginning.
And I'm sad for Ahmed that his father is dragging him off on some pilgrimage to Mecca. The kid needs to stay in school and keep learning. And he needs to hang out at a maker space after school with like minded people.

[adprom]

Okay I can accept that, even though it may be considered impolite, that's okay there are a number of cultural differences between AU and US.

It's just slang - not impolite. Blog forum of an aussie blogger - I'm willing to take a punt that our slang is fine here

Perhaps; but consider what we don't know about the story.
Far too many details missing to rule out any one source of information at this time.

Quoting unsubstantiated sources is akin to making it up which will always attract scrutiny. The problem is that claims were cited as fact, without any evidence. Quite rightfully, the obligation is on the party making said claims to prove they are correct. It is not up to another party to prove them wrong.

Otherwise I could say Ahmed's mother was a prostitute and state it as a fact and then argue against those who disagree demanding they show evidence to show I was wrong. Obviously this would be absurd.

And you have evidence the clock was only disassembled? please lets see it.

You don't seem to understand how this works. You are making claims without evidence, the impetus is on you to prove it - not for others to prove the negative assertion. This is basic stuff (something which conspiracy theorists and 'truthers' tend not make a mistake with.

I get that but it needs to be applied all the way around, including to those stories you and others like Dave favor.

No - it really doesn't that would be completely flawed. Someone who is introducing new information has the burden upon them to provide satisfactory proof that it is true.

One related thought;
The difference between a skeptic and a debunker is a skeptic is always after the truth, a debunker could care less about the truth when it doesn't fit his or her agenda.
I am the skeptic. And for now I am done with this urinating contest, I have better things to do like get on the radio and talk to my friends in Northern Kalifornia.

Not quite true. A sceptic is someone who habitually doubts the claims made. There is no assumption that this is rational. Rationality may or may not exist. There is no shortage of irrational sceptics out there (climate change, 9/11 truthers etc etc).

A debunker  is someone who takes a demonstrably false claim and shows it to be so. They don't necessarily take a particular position. To expose a false belief or idea as false is to debunk. In scientific circles, debunking is quite an objective process which requires clear evidence (as dave has done with Batteriser).

[EEVblog]

A debunker  is someone who takes a demonstrably false claim and shows it to be so. They don't necessarily take a particular position. To expose a false belief or idea as false is to debunk. In scientific circles, debunking is quite an objective process which requires clear evidence (as dave has done with Batteriser).

"Debunking" is quite an interesting concept. As often a debunker might indeed start out from an opinionated viewpoint, and sets about to prove it. That could be looked upon as bad, as starting out from a viewpoint can introduce bias etc, but a good debunking is one that sticks to the facts that are verifiable by others knowledgeable in the field, and even gives benefit of the doubt (playing devils advocate) as part of the debunking process. Ultimately though it always falls down to demonstrable facts to prove your case of course.

[AF6LJ]

Firstly, in Australia dude is regularly used as a general reference without implying gender. No need to get your knickers in a knot.

Okay I can accept that, even though it may be considered impolite, that's okay there are a number of cultural differences between AU and US.

Another example: I call girls "guys" all the time. If I see a bunch of girls I know I go "hi guys". Guys is just the common collective term.

No big deal the same happens here. You guys" has no gender attached to it here also. 

What you have stated so far is no more than an unproven conspiracy.

Perhaps; but consider what we don't know about the story.

Why are people unable to simply leave it at that?
This whole thing has bought out the worse in people, it's embarrassing.
When I first released the video and that blog post about the clock being a Radio Shack thing hadn't been posted yet, almost everyone was in support of Ahmed.
But then suddenly it went viral that it wasn't his design (even though that was obvious and even he said it was a 10-20min job), and the world went ape shit and turned on him. As if it's the greatest fraud in history that a 14yo kid overated his skills and used the wrong word to describe what he did.
And people accuse me of being manipulated by the media 

There were other issues; had his father simply been a manager at a 7-11 or something there would be no uproar over the incident.
Obama getting involved added to the suspicion.
There is a lot of internal politics involved in this issue including a known race pimping president.

Far too many details missing to rule out any one source of information at this time.

You have zero sources of information that confirm your assertion.
You and others just want to ride the Ahmed hate train because *insert reason here*

Sorry but that isn't true, I appeal to your sense of logic, at best we only have third hand testimony.
The news report wouldn't stand up in court if it were admitted as the testimony of a witness.
Dave I know you are too smart to fall for the "hate" canard.

So that's the point, if you make a claim, it is up to you to prove them with evidence. Not for me to provide evidence otherwise.

I get that, but

No, you don't get it. There is no but. You made a claim, you provide the evidence, or you get rightfully get shot down in flames for it.

I totally get it Dave; I don't gulp media Kool Aid or engorge myself in a banquet of media bullshit.

but it needs to be applied all the way around, including to those stories you and others like Dave favor.

The only story I favor is giving a 14yo electronics hobbyists the benefit of any doubt. I'm guilty as charged.
If it turns out all the conspiracy stuff is all true, so be it. People can say "I told you so" all they like, they will still be the ones who were too pathetic enough to give a 14yo kid the benefit of the doubt.

It is sad the child was used like this. Keep in mind you are talking about a country where the school droids suspend a child for eating a pop tart into the shape of a gun. You need to live here to fully understand the high degree of fear and stupidity that rules this country as it is being destroyed from within.

The difference between a skeptic and a debunker is a skeptic is always after the truth, a debunker could care less about the truth when it doesn't fit his or her agenda.
I am the skeptic.

No, you are not. You have stated certain facts as being, and I quote you "all factual.". When pressed for evidence for that statement you haven't giving any. An agenda if there ever was one!

So now I have to go and buy a radio shack alarm clock and modify it to count down, just so you can say it was not the same alarm clock or it didn't use the same chip, when you have no idea whatsoever what chip or how the board had been modified in said clock? That is a stretch sir.

Many people know my strong thoughts on religion, Islam, and you can likely guess what I think of Ahmed's father, and yet I still support Ahmed - why?
Well, I can either give up on a 14yo kid and join the whole world in chorus about how he's a "fraud", and crap on about his family ties etc, but how is that going to help him?
Why are so many people now willing to throw a 14yo kid to the fire?
This story has turned an order of magnitude sader than I thought it was at the beginning.
And I'm sad for Ahmed that his father is dragging him off on some pilgrimage to Mecca. The kid needs to stay in school and keep learning. And he needs to hang out at a maker space after school with like minded people.

I know why you support him and I am all with you on that, however we still don't know all the facts.
Again I appeal to your inner sense of logic.
We, including you know next to nothing about the actual events in question.

[zapta]

There is a master clock for each grid authority.  In the US we have three major grids:  West, East, and Texas ERCOT. 

The west coast is long and thus has significant phase difference between the ends, right? 

Assigning the optimal phase for each node on the grid is an interesting computational problem which I am sure was researched extensively. It's interesting to know how well it is solved by the local approach where each node just phase locks to its feed. It's also interesting to know if when they design the grid (e.g. adding lines), the include phase consistency considerations.

Dave had an episode where he visited a TV station. Would be interesting to see a similar one with a power station.

[EEVblog]

There were other issues; had his father simply been a manager at a 7-11 or something there would be no uproar over the incident.
Obama getting involved added to the suspicion.
There is a lot of internal politics involved in this issue including a known race pimping president.

Of course, no argument from me.

You have zero sources of information that confirm your assertion.

Sorry but that isn't true

That part is. Your continued inability to provide evidence to back up your claim is still noted.

I totally get it Dave; I don't gulp media Kool Aid or engorge myself in a banquet of media bullshit.

As above.

It is sad the child was used like this.

He is getting and will get use, yes, it's sad. His father and anyone else who can will ride this dog and pony show for all it's worth.

You need to live here to fully understand the high degree of fear and stupidity that rules this country as it is being destroyed from within.

Err, could have sworn I made a video talking about that...

So now I have to go and buy a radio shack alarm clock and modify it to count down, just so you can say it was not the same alarm clock or it didn't use the same chip, when you have no idea whatsoever what chip or how the board had been modified in said clock? That is a stretch sir.

You made a claim, you get to prove it. This is getting tiring.

I know why you support him and I am all with you on that, however we still don't know all the facts.

You'll get no argument from me on that.

Again I appeal to your inner sense of logic.
We, including you know next to nothing about the actual events in question.

Again, no argument.
So why try and shoot me down in flames for giving a 14yo kid the benefit of the doubt until facts do actually come in that tell a different story?
And BTW, even if it turns out he was setup/used/whatever, it's still ok to support a 14yo kid and help him. You can still support the kid and believe the conspiracies, they aren't mutually exclusive positions.
Personally I hope the kid does get a scholarship and moves to a school where he is surrounded by nothing but secular technical minded people.
Does he "deserve it" based on merit?, of course not, he seems to have little to no real technical skills or accomplishments, but I can still hope that happens for him.

[EEVblog]

Dave had an episode where he visited a TV station. Would be interesting to see a similar one with a power station.

It's on my blog wish-list (a.k.a get off my arse list).

[linux-works]

I don't really want to re-open this (now old) debate; but when people throw around things that have no citations, they need to be called out for it.

I looked and tried but could not find a single credible citation for this 'count down' notion that some posters are trying to have us believe.

either post something credible, applogize that you simply repeated conservative talking points on some blog, or shut the hell up already.  I think we've had enough spin on this from people trying to use this to forward their agenda.  put up or PLEASE just shut up.

(I start to wonder; should there be time-outs for people who insist on posting blatant lies and when called on it, cannot provide any backup?  if there is no negative consequences for posting lies, people will continue to do it.)

[asgard]

http://www.thedailybeast.com/articles/2015/09/21/nerds-rage-over-ahmed-s-clock.html

http://news.investors.com/ibd-editorials/092215-772291-did-muslim-clock-boy-perpetuate-hoax.htm

http://www.theguardian.com/science/2015/sep/20/richard-dawkins-questions-ahmed-mohamed-motive-backlash

http://www.nationalreview.com/corner/ahmed-mohamed-clock-bomb-media-narrative-ian-tuttle

http://toprightnews.com/uh-oh-this-is-what-happened-when-ahmeds-clock-invention-was-reverse-engineered/

http://ethicsalarms.com/2015/09/24/it-looks-like-ahmeds-cool-clock-was-a-hoax-after-all-now-what/

http://dfwci.com/blog4/ahmeds-clock-is-not-an-invention/

[LabSpokane]

There is a master clock for each grid authority.  In the US we have three major grids:  West, East, and Texas ERCOT. 

The west coast is long and thus has significant phase difference between the ends, right? 

I think that has historically been the issue with large grids, which leads to instability. That's the idea with synchrophasors that each generator station has a very accurate reference to a common clock. 

[KedasProbe]

Why was, or better put, who marked this as private?

Obviously he is hiding a bomb 

[linux-works]

(mess of blogs, bullshit and right-wing nutterscreeds deleted)

what point were you trying to make?

none of those are trusted sources.  not sure what your purpose was in posting that crap.  actually, I suspect I know ;(

[AF6LJ]

There were other issues; had his father simply been a manager at a 7-11 or something there would be no uproar over the incident.
Obama getting involved added to the suspicion.
There is a lot of internal politics involved in this issue including a known race pimping president.

Of course, no argument from me.

You have zero sources of information that confirm your assertion.

Sorry but that isn't true

That part is. Your continued inability to provide evidence to back up your claim is still noted.

I totally get it Dave; I don't gulp media Kool Aid or engorge myself in a banquet of media bullshit.

As above.

It is sad the child was used like this.

He is getting and will get use, yes, it's sad. His father and anyone else who can will ride this dog and pony show for all it's worth.

You need to live here to fully understand the high degree of fear and stupidity that rules this country as it is being destroyed from within.

Err, could have sworn I made a video talking about that...

So now I have to go and buy a radio shack alarm clock and modify it to count down, just so you can say it was not the same alarm clock or it didn't use the same chip, when you have no idea whatsoever what chip or how the board had been modified in said clock? That is a stretch sir.

You made a claim, you get to prove it. This is getting tiring.

I know why you support him and I am all with you on that, however we still don't know all the facts.

You'll get no argument from me on that.

Again I appeal to your inner sense of logic.
We, including you know next to nothing about the actual events in question.

Again, no argument.
So why try and shoot me down in flames for giving a 14yo kid the benefit of the doubt until facts do actually come in that tell a different story?
And BTW, even if it turns out he was setup/used/whatever, it's still ok to support a 14yo kid and help him. You can still support the kid and believe the conspiracies, they aren't mutually exclusive positions.
Personally I hope the kid does get a scholarship and moves to a school where he is surrounded by nothing but secular technical minded people.
Does he "deserve it" based on merit?, of course not, he seems to have little to no real technical skills or accomplishments, but I can still hope that happens for him.

I am going to address two things; then I am done not because of there being any "winner or looser" in this discussion; but because we are getting nowhere here.

First off.
As I stated we have no real information regarding the actual events surrounding this child, or the incident, we only have third hand testimony, hearsay, as a matter of fact it could be considered gossip, but some people take the word of the news media as the word of God. What passes for news in this day and age is seldom real news.

The other issue Dave;
I am not attacking you, just your position. There is a difference.
I respect you, I just think you give the news media the credit it doesn't deserve.

I am done you and everyone else get the last word.
 

[Fungus]

So now I have to go and buy a radio shack alarm clock and modify it to count down, just so you can say it was not the same alarm clock or it didn't use the same chip, when you have no idea whatsoever what chip or how the board had been modified in said clock? That is a stretch sir.

Nope. This is the fail.

You don't have to prove that it can be done, you have to prove that it WAS done.

[linux-works]

As I stated we have no real information regarding the actual events surrounding this child

so, just STFU then!

but actually, we do have info.  we know that if there was a 'count-down' feature added, that it would have been mentioned day-0 or day-1 at worst.  why is this being added to the conservate hate-blog talking points?  because they don't have enough real stuff to hate on this poor boy and, as faux news watchers regularly do, they make anything up they want and label it as 'fact' just to try to own the discussion and swerve it their way.

if you have facts, show an API or other news source and not some stupid hate-mongers blog!

or, again, just stfu.

[zapta]

...they don't have enough real stuff to hate on this poor boy...

Linux Works, you come to a conclusion without having the facts and then you complain that others  do the same and arrive to a different conclusion.

Your strong opinion is as unjustified as theirs.

[drws]

If I may just take the thread off topic and ask about the video... 

The part where the e, f, g segments are tapped to reset the chip, I just can't get my head around (and I know it will be simple).
I can see why, you don't have BCD output to do the reset, its more the voltage and current flow parts I'm trying to understand.
In the image I've attached, is the up arrow and resistor (in the blue circle) attached to the supply voltage / common 'logic high' voltage (not sure on the correct term, I don't mean 240v)?

The LEDs are common cathode where you set e, f and g 'high' if you want to light them, so then I see that conventional current travels down (the red highlighted cables) to the diodes which are reversed-biased from that perspective?
Then I got confused.

I've tried to go off and understand what is going on and come to this conclusion below. If the more experienced people (and to be honest Probes the Monkey is probably more experienced than me) could let me know if I'm in the right ballpark please.
Is it because when the segments are off, the red and green circled parts are 0v which means the right-hand side of the three diodes must be +0.6v or +1.8v? (because of diode forward Vdrop or 3x Vdrop?) and the resistor has to drop the supply voltage down to 0.6v/1.8v?
Then when the segments e,f and g go 'high' to Vsupply then the right of the diodes is Vsupply-0.6v which turns on the transistor? (i.e. the resistor doesn't need to drop as much voltage now.)

Not sure what happens when just one segment (or two) are high. The concept of an And gate I get, it just doesn't look like an And gate to me.
What is the voltage on the right of the three diodes when just one segment is lit?

*edit for some grammar.

[zapta]

The concept of an And gate I get, it just doesn't look like an And gate.

It is an AND gate. The output on the right side of the diodes is high only when the three inputs are high. A single low input forces the output to be low.  Draw the truth table and see what you get.

The only issue here is the inputs to the and gate are not standard 0-5V signals. That's why one transistor to amplify and another one to invert (other wise you would and with a NAND gate).

Dave could save one transistor and implement a NOR gate but I presume the seven segments sequence doesn't happen to have a set of output that are all low at 6 but not at 0-5. It's a kind of an opportunistic or trick design.

[drws]

I see, so the presence of even one diode with 0v on the left side will make the right side where all three meet always be 0.6v.
I'm ok with the truth table side of it, just trying to understand the physical side of it. I've only had the pleasure of using gates in the CMOS DIP variety. Maybe I should try and build one from just diodes.

[zapta]

I see, so the presence of even one diode with 0v on the left side will make the right side where all three meet always be 0.6v.
I'm ok with the truth table side of it, just trying to understand the physical side of it. I've only had the pleasure of using gates in the CMOS DIP variety. Maybe I should try and build one from just diodes.

This may help

https://en.wikipedia.org/wiki/Diode%E2%80%93transistor_logic

[Jr460]

Dave had an episode where he visited a TV station. Would be interesting to see a similar one with a power station.

It's on my blog wish-list (a.k.a get off my arse list).

Started off as a EE at a power station.  Not that much that is cool from an EE perspective unless you really know where to look.  The size and scale of things is very amazing.

I ended up mainly being the turbine guy for outages.  Each year a unit is taken down for a week or more for maintenance work.  Depending on what you know needs to be done, and what you suspect needs to be done, you must have all the spare parts around and ready to go.  Lots of planning.  Bring a unit back online after outage is timed so that someone else in the region can take their unit down.  I heard an unscheduled outage cost about $1,000,000 a day.

In terms of overall system control, that is handled not a at each station, but at some central company office.  That gets fun. 

One task is to keep the overall system freq. good over a 24 hour period.  So the software keeps a running total of how slow or fast the system has been.  Another goal is to generate what your local customers are using.  The next goal is to let X power flow in or out of your system based on who much you owe other companies, or they owe you.  (Some units are jointly owned and while you run the unit, someone else pays X%, you owe them X% of the power that unit generates).  And last but not least, tweak the amount of each of your units so that overall you are getting that power with the least amount of fuel.

The last part requires that you have curves for each unit of Heat Rate vs Mega Watts.  Most units get inefficient to run when under 50% loaded.  Those curves get computed by detailed load tests at least once a year under a bunch of conditions.  Not only do you need additional sets of temp, press, and flow measurements from all over the unit, you need exact careful lab work on the coal that was used during the test.  (Each barge of coal is different in the BTU per pound, water, ash and sulfur.  The coal lab at each plant runs almost all the time.)

Let me know, I'll be glad to answer anything I can remember.

[zapta]

Let me know, I'll be glad to answer anything I can remember.

I have many questions but they will be out of topic here. ;-)

Just a quick one, when you work in a power station, are you busy all time or just letting the computers do their job and waiting for the next incident?

[drws]

I see, so the presence of even one diode with 0v on the left side will make the right side where all three meet always be 0.6v.
I'm ok with the truth table side of it, just trying to understand the physical side of it. I've only had the pleasure of using gates in the CMOS DIP variety. Maybe I should try and build one from just diodes.

This may help

https://en.wikipedia.org/wiki/Diode%E2%80%93transistor_logic

Excellent, thanks. Its starting to sink in now. I knocked up a quick simulation and I can see the effect now of all off, some on and all on for the DTL AND gate, current paths and voltages etc.

Another noobie follow on question...
When I first saw the diagram (at the part where Dave paused the video for us to guess what was wrong) I was expecting the current to flow down through the resistor, then left through all three diodes (with a slight voltage drop) up through the three segments of the display (e,f,g - lighting them permanently) and through the common cathode+resistor to ground to complete the circuit. This would be whilst the 4026 was low for those segments.

Does the 4026 sink the current as well when its low on those pins or does the total path have too much resistance/voltage drop to light the segments?